As it is unstable, all isotopes of polonium are radioactive. There is disagreement as to whether polonium is a post-transition metalor metalloid.[2][3]
Characteristics
Polonium has 33 known isotopes, all of which are radioactive. They have atomic masses that range from 188 to 220 u. 210Po (half-life 138.4 days) is the most widely available. Sony VAIO VPCEB1LFX/BI Battery
209Po (half-life 103 years) and 208Po (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron.
210Po is an alpha emitter that has a half-life of 138.4 days; it decays directly to its stable daughter isotope, 206Pb. A milligram of 210Po emits about as many alpha particles per second as 4.5 grams of 226Ra. Sony VAIO VPCEB1LFX/WI Battery
A few curies (1 curie equals 37gigabecquerels, 1 Ci = 37 GBq) of 210Po emit a blue glow which is caused by excitation of surrounding air. A single gram of210Po generates 140 watts of power.[4] Because it emits many alpha particles, which are stopped within a very short distance in dense media and release their energy, 210Po has been used as a lightweight heat source to power thermoelectric cells inartificial satellites; Sony VAIO VPCEB1MFX Battery
for instance, 210Po heat source was also used in each of the Lunokhod rovers deployed on the surface of the Moon, to keep their internal components warm during the lunar nights.[5] Some anti-static brushes contain up to 500 microcuries (20 MBq) of 210Po as a source of charged particles for neutralizing static electricity in materials like photographic film.[6] Sony VAIO VPCEB1MFX/BI Battery
About one in 100,000 alpha emissions causes an excitation in the nucleus which then results in the emission of a gamma ray.[7]Because of its relatively high rate of alpha emissions, only about 1 in 100,000 result in releasing a gamma ray. But it is the alpha particles, not the side effect of an occasional gamma ray, that results in 210Po decay. Sony VAIO VPCEB1NFX Battery
Low gamma output renders gamma detection nearly impossible, with any emitted gamma nearly indistinguishable from background radiation. At 4.001 u, the alpha particle is too massive to penetrate most barriers, including intact human epidermis. If the skin is broken however, or the alpha emitter is ingested or inhaled, the high charge on the alpha particle will result in severe cellular damage. Sony VAIO VPCEB1NFX/B Battery
The high alpha decay of polonium renders alpha detection as the preferred method of quantifying this isotope in the laboratory.
Solid state form
Polonium is a radioactive element that exists in two metallic allotropes. The alpha form is the only known example of a simple cubiccrystal structure in a single atom basis, with an edge length of 335.2 picometres; the beta form is rhombohedral.[8][9] Sony VAIO VPCEB1NFX/L Battery
The structure of polonium has been characterized by X-ray diffraction [10][11] and electron diffraction.[12]
210Po (in common with 238Pu) has the ability to become airborne with ease: if a sample is heated in air to 55 °C (131 °F), 50% of it is vaporized in 45 hours, even though the melting point of polonium is 254 °C (489 °F) and its boiling point is 962 °C (1763 °F).[13][14] Sony VAIO VPCEB1NFX/P Battery
More than one hypothesis exists for how polonium does this; one suggestion is that small clusters of polonium atoms are spalled offby the alpha decay.
Chemistry
The chemistry of polonium is similar to that of tellurium and bismuth. Polonium dissolves readily in dilute acids, but is only slightly soluble in alkalis. Sony VAIO VPCEB1NFX/W Battery
The hydrogen compound PoH2 is liquid at room temperature (melting point ?36.1°C, boiling point35.3°C). Halides of the structure PoX2, PoX4 and PoX6 are known. The two oxides PoO2and PoO3 are the products of oxidation of polonium.[15]
It has been reported that some microbes can methylate polonium by the action of methylcobalamin.[16][17] Sony VAIO VPCEB1PFX Battery
This is similar to the way in which mercury, selenium and tellurium are methylated in living things to create organometallic compounds. As a result when considering the biochemistry of polonium one should consider the possibility that the polonium will follow the same biochemical pathways as selenium and tellurium. Sony VAIO VPCEB1PFX/B Battery
Also tentatively called "Radium F", polonium was discovered by Marie Sk?odowska-Curie and her husband Pierre Curie in 1898[18]and was named after Marie Curie's native land of Poland (Latin: Polonia)[19][20] Poland at the time was under Russian, Prussian, and Austrian partition, and did not exist as an independent country. Sony VAIO VPCEB1QGX Battery
It was Curie's hope that naming the element after her native land would publicize its lack of independence. Polonium may be the first element named to highlight a political controversy.[21]
This element was the first one discovered by the Curies while they were investigating the cause of pitchblende radioactivity. Sony VAIO VPCEB1QGX/BI Battery
The pitchblende, after removal of the radioactive elements uranium and thorium, was more radioactive than both the uranium and thorium put together. This spurred the Curies on to find additional radioactive elements. The Curies first separated out polonium from the pitchblende, and then within a few years, also isolated radium. Sony VAIO VPCEB1RGX Battery
Because of the small quantities present in nature, isolation of polonium from natural sources is complicated. The largest ever isolated batch from 37 tonnes of residues from radium production yielded only 40 Ci of polonium-210.[22] Sony VAIO VPCEB1RGX/BI Battery
Gamma counting
By means of radiometric methods such as gamma spectroscopy (or a method using a chemical separation followed by an activitymeasurement with a non-energy-dispersive counter), it is possible to measure the concentrations of radioisotopes and to distinguish one from another. Sony VAIO VPCEB20 Battery
In practice, background noise would be present and depending on the detector, the line width would be larger which would make it harder to identify and measure the isotope. In biological/medical work it is common to use the natural 40K present in all tissues/body fluids as a check of the equipment and as an internal standard. Sony VAIO VPCEC20 Battery
Alpha counting
The best way to test for (and measure) many alpha emitters is to use alpha-particle spectroscopy as it is common to place a drop of the test solution on a metal disk which is then dried out to give a uniform coating on the disk. This is then used as the test sample. Sony VAIO VPCEE20 Battery
If the thickness of the layer formed on the disk is too thick then the lines of the spectrum are broadened, this is because some of the energy of the alpha particlesis lost during their movement through the layer of active material. An alternative method is to use internal liquid scintillation where the sample is mixed with a scintillation cocktail. Sony VAIO VPCEF20 Battery
When the light emitted is then counted, some machines will record the amount of light energy per radioactive decay event. Due to the imperfections of the liquid scintillation method (such as a failure for all the photons to be detected, cloudy or coloured samples can be difficult to count) and the fact that random quenching can reduce the number of photons generated per radioactive decay it is possible to get a broadening of the alpha spectra obtained through liquid scintillation. Sony VAIO VPCF112FX/B Battery
It is likely that these liquid scintillation spectra will be subject to a Gaussian broadeningrather than the distortion exhibited when the layer of active material on a disk is too thick.
A third energy dispersive method for counting alpha particles is to use a semiconductor detector. Sony VAIO VPCF115FG/B Battery
From left to right the peaks are due to 209Po, 210Po, 239Pu and 241Am. The fact that isotopes such as 239Pu and 241Am have more than one alpha line indicates that the nucleus has the ability to be in different discrete energy levels (like a molecule can).
Occurrence and production
Polonium is a very rare element in nature because of the short half-life of all its isotopes. Sony VAIO VPCF116FGBI Battery
It is found in uranium ores at about 100 micrograms per metric ton (1 part in 1010), which is approximately 0.2% of the abundance of radium. The amounts in the Earth's crust are not harmful. Polonium has been found in tobacco smoke from tobacco leaves grown with phosphatefertilizers.[23][24][25] Sony VAIO VPCF117FJ/W Battery
Synthesis by (n,?) reaction
In 1934 an experiment showed that when natural 209Bi is bombarded with neutrons, 210Bi is created, which then decays to 210Po via ? decay. The final purification is done pyrochemically followed by liquid-liquid extraction techniques.[26] Sony VAIO VPCF117HG/BI Battery
Polonium may now be made in milligram amounts in this procedure which uses high neutron fluxes found in nuclear reactors. Only about 100 grams are produced each year, practically all of it in Russia, making polonium exceedingly rare.[27][28] Sony VAIO VPCF118FJ/W Battery
Synthesis by (p,n) and (p,2n) reactions
It has been found that the longer-lived isotopes of polonium can be formed by proton bombardment of bismuth using a cyclotron. Other more neutron rich isotopes can be formed by the irradiation of platinum with carbon nuclei.[29] Sony VAIO VPCF119FC Battery
Applications
When it is mixed or alloyed with beryllium, polonium can be a neutron source: beryllium releases a neutron upon absorption of an alpha particle that is supplied by210Po. It has been used in this capacity as a neutron trigger or initiator for nuclear weapons.[30]Other uses include the following. Sony VAIO VPCF119FC/BI Battery
Devices that eliminate static charges in textile mills and other places.[31] However, beta particle sources are more commonly used and are less dangerous. A non-radioactive alternative is to use a high-voltage DC power supply to ionise air positively or negatively as required.[32] Sony VAIO VPCF119FJ/BI Battery
- 210Po can be used as an atomic heat source to power radioisotope thermoelectric generators via thermoelectricmaterials.[33]
- Because of its very high toxicity, polonium can be used as a poison (see, for example, Alexander Litvinenko poisoning).
Polonium-containing anti-static brushes are used to remove dust on photographic film.[34] Sony VAIO VPCF11AFJ Battery
Overview
By mass, polonium-210 is around 250,000 times more toxic than hydrogen cyanide (the actual LD50 for 210Po is less than 1 microgram for an average adult (see below) compared with about 250 milligrams for hydrogen cyanide[35]). The main hazard is its intense radioactivity (as an alpha emitter), which makes it very difficult to handle safely: Sony VAIO VPCF11AGJ Battery
one gram of Po will self-heat to a temperature of around 500 °C (932 °F).[4] Even in microgram amounts, handling 210Po is extremely dangerous, requiring specialized equipment (a.o., alpha glove box under depression and equipped with high performance filters), adequate monitoring, and strict handling procedures to avoid any contamination. Sony VAIO VPCF11AHJ Battery
Alpha particles emitted by polonium will damage organic tissue easily if polonium is ingested, inhaled, or absorbed, although they do not penetrate the epidermis and hence are not hazardous as long as the alpha particles remain outside of the body. Meanwhile, bearing chemically resistant and "intact" gloves is a mandatory precautions to avoid transcutaneous diffusion of polonium directly through the skin. Sony VAIO VPCF11JFX/B Battery
Polonium delivered in concentrated nitric acid can easily diffuse through inadequate gloves (e.g., latex gloves) or the acid may damage the gloves.
Acute effects
The median lethal dose (LD50) for acute radiation exposure is generally about 4.5 Sv.[36] The committed effective dose equivalent210Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled.[37] Sony VAIO VPCF11M1E Battery
Since 210Po has an activity of 166 TBq per gram (4,500 Ci/g)[37](1 gram produces 166×1012 decays per second), a fatal 4.5 Sv (J/kg) dose can be caused by ingesting 8.8 MBq (238 microcuries, µCi), about 50 nanograms (ng), or inhaling 1.8 MBq (48 µCi), about 10 ng. One gram of 210Po could thus in theory poison 20 million people of whom 10 million would die. Sony VAIO VPCF11M1E/H Battery
The actual toxicity of 210Po is lower than these estimates, because radiation exposure that is spread out over several weeks (the biological half-life of polonium in humans is 30 to 50 days[38]) is somewhat less damaging than an instantaneous dose. It has been estimated that a median lethal dose of 210Po is 0.015 GBq (0.4 mCi), or 0.089 micrograms, still an extremely small amount.[39][40] Sony VAIO VPCF11MFX/B Battery
Long term (chronic) effects
In addition to the acute effects, radiation exposure (both internal and external) carries a long-term risk of death from cancer of 5–10% per Sv.[36] The general population is exposed to small amounts of polonium as a radon daughter in indoor air; Sony VAIO VPCF11S1E Battery
the isotopes 214Po and 218Po are thought to cause the majority[41] of the estimated 15,000-22,000 lung cancer deaths in the US every year that have been attributed to indoor radon.[42] Tobacco smoking causes additional exposure to polonium.[43]
Regulatory exposure limits
The maximum allowable body burden for ingested 210Po is only 1.1 kBq (30 nCi), which is equivalent to a particle massing only 6.8 picograms. Sony VAIO VPCF11S1E/B Battery
The maximum permissible workplace concentration of airborne 210Po is about 10 Bq/m3 (3 × 10?10 µCi/cm3).[44] The target organs for polonium in humans are the spleen and liver.[45] As the spleen (150 g) and the liver (1.3 to 3 kg) are much smaller than the rest of the body, if the polonium is concentrated in these vital organs, it is a greater threat to life than the dose which would be suffered (on average) by the whole body if it were spread evenly throughout the body, in the same way as caesium or tritium (as T2O). Sony VAIO VPCF11Z1E Battery
210Po is widely used in industry, and readily available with little regulation or restriction. In the US, a tracking system run by the Nuclear Regulatory Commission will be implemented in 2007 to register purchases of more than 16 curies (590 GBq) of polonium 210 (enough to make up 5,000 lethal doses). Sony VAIO VPCF11Z1E/BI Battery
The IAEA "is said to be considering tighter regulations... There is talk that it might tighten the polonium reporting requirement by a factor of 10, to 1.6 curies (59 GBq)."[46]
Famous poisoning cases
Notably, the murder of Alexander Litvinenko, a Russian dissident, in 2006 was announced as due to 210Po poisoning[47][48](see Alexander Litvinenko poisoning). Sony VAIO VPCF11ZHJ Battery
According to Prof. Nick Priest of Middlesex University, an environmental toxicologist and radiation expert, speaking on Sky News on December 2, Litvinenko was probably the first person ever to die of the acute ?-radiation effects of 210Po.[49]
It has also been suggested that Irène Joliot-Curie was the first person ever to die from the radiation effects of polonium (due to a single intake) in 1956.[50] Sony VAIO VPCF127HGBI Battery
She was accidentally exposed to polonium in 1946 when a sealed capsule of the element exploded on her laboratory bench. A decade later, on 17 March 1956, she died in Paris from leukemia which may have been caused by that exposure.
According to the book The Bomb in the Basement, several death cases in Israel during 1957-1969 were caused by 210Po.[51] Sony VAIO VPCF137HG/BI Battery
A leak was discovered at a Weizmann Institutelaboratory in 1957. Traces of 210Po were found on the hands of professor Dror Sadeh, a physicist who researched radioactive materials. Medical tests indicated no harm, but the tests did not include bone marrow. Sadeh died from cancer. Sony VAIO VPC-P111KX/B Battery
One of his students died of leukemia, and two colleagues died after a few years, both from cancer. The issue was investigated secretly, and there was never any formal admission that a connection between the leak and the deaths had existed.[52]
Treatment
It has been suggested that chelation agents such as British Anti-Lewisite (dimercaprol) can be used to decontaminate humans.[53] Sony VAIO VPC-P111KX/D Battery
In one experiment, rats were given a fatal dose of 1.45 MBq/kg (8.7 ng/kg) of 210Po; all untreated rats were dead after 44 days, but 90% of the rats treated with the chelation agent HOEtTTC remained alive after 5 months.[54] Sony VAIO VPC-P111KX/G Battery
Commercial products containing polonium
Potentially lethal amounts of polonium are present in anti-static brushes sold to photographers.[55] In USA, the devices with no more than 500 µCi of (sealed) 210Po per unit can be bought in any amount under a "general license",[56] which means that a buyer need not be registered by any authorities. Sony VAIO VPC-P111KX/P Battery
Tiny amounts of such radioisotopes are sometimes used in the laboratory and for teaching purposes—typically of the order of 4–40 kBq (0.1–1.0 µCi), in the form of sealed sources, with the polonium deposited on a substrate or in a resin or polymer matrix—are often exempt from licensing by the NRC and similar authorities as they are not considered hazardous. Sony VAIO VPC-P111KX/W Battery
Small amounts of 210Po are manufactured for sale to the public in the United States as 'needle sources' for laboratory experimentation, and are retailed by scientific supply companies. The actual polonium is a layer of plating which in turn is plated with a material such as gold. Sony VAIO VPC-P112KX/B Battery
This allows the alpha radiation (used in experiments such as cloud chambers) while preventing the polonium from being released and presenting a toxic hazard. According to United Nuclear, they typically sell between four and eight sources per year.[57][58]
Occurrence in humans and the biosphere
The natural occurrence of polonium-210 is widespread in the biosphere, including in human tissues. Sony VAIO VPC-P112KX/D Battery
This is a consequence of a mechanistic chain involving naturalradioactive fallout. Radium-226 in the Earth's crust decays with the production of radon-220, some of which, during its 3.6-day half-life, diffuses into the atmosphere. Here it decays with the production of polonium-210, much of which, during its 138-day half-life, is washed back down to the Earth's surface, thus entering the biosphere.[59][60][61] Sony VAIO VPC-P112KX/G Battery
As early as the 1920s Lacassagne, using polonium provided by his colleague Marie Curie, showed that the element has a very specific pattern of uptake in rabbit tissues, with high concentrations particularly in liver, kidney and testes.[62] More recent evidence suggests that this behaviour results from polonium substituting for sulphur in S-containing amino-acids or related molecules[63][64] Sony VAIO VPC-P112KX/P Battery
and that similar patterns of distribution occur in human tissues.[65] Polonium is indeed an element naturally present in all humans, contributing appreciably to natural background dose, with wide geographical and cultural variations, and particularly high levels in arctic residents, for example.[66] Sony VAIO VPC-P112KX/W Battery
Tobacco
The presence of polonium in tobacco smoke has been known since the early 1960s.[67][68] Some of the world's biggest tobacco firms researched ways to remove the substance—to no avail—over a 40-year period but never published the results.[25] Sony VAIO VPCP113KX/B Battery
Radioactive polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants (such as tobacco) and stored in its tissues.[69][70][71] Tobacco plants fertilized by rock phosphates contain polonium-210, which emits alpha radiation estimated to cause about 11,700 lung cancer deaths annually worldwide. Sony VAIO VPC-P113KX/B Battery
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table. Sony VAIO VPCP113KX/D Battery
However, research has shown this element follows periodic trends, being the heaviest known halogen, with melting and boiling points being higher than those of lighter halogens.
Astatine was first produced by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè in the University of California, Berkeley in 1940. Sony VAIO VPC-P113KX/D Battery
Three years later, it was found in nature; however, with an estimated amount of less than 28 grams (1 oz) at given time, astatine is the least abundant element in Earth's crust among non-transuranium elements. Among astatine isotopes, six (with mass numbers 214 to 219) are present in nature, but the most stable astatine-210 is not. Sony VAIO VPCP113KX/G Battery
The second longest-living astatine-211 is the only one to find a commercial use, being useful as an alpha emitter in medicine; however, only extremely small quantities are used, and in larger ones it is very hazardous, as it is intensely radioactive.
Until recently most of the chemical characteristics of astatine were inferred from comparison with other elements; however, important studies have already been done. Sony VAIO VPC-P113KX/G Battery
The main difference between astatine and iodine is that the HAt molecule is chemically a hydride rather than a halide; however, in a fashion similar to the lighter halogens, it is known to form ionic astatides with metals. Bonds to nonmetals result in positive oxidation states, with +1 best portrayed by monohalides and their derivatives, while the higher are characterized by bond to oxygen and carbon. Sony VAIO VPCP113KX/P Battery
Attempts to synthesize astatine fluoride have been met with failure.
General characteristics
Astatine is a highly radioactive element: its isotopes have their half-lives under half a day, decaying into those ofbismuth, polonium, radon, or other astatine isotopes. Among the first 103 elements, only francium and nobelium, the latter of which does not occur in nature, are less stable than astatine.[1] Sony VAIO VPC-P113KX/P Battery
Astatine is a halogen,[2] though it is more metallic than iodine. Research into astatine is limited by the very small quantities available, which is a consequence of its extremely short half-life;[3] however, it has been shown that astatine suits most periodic trends very well. Like other halogens, it is composed of diatomic At2 molecules on standard conditions.[4] Sony VAIO VPCP113KX/W Battery
Its melting and boiling point are estimated about 300 °C (575 °F) and 370 °C (700 °F), respectively. This allows astatine to fit well the trend in increase in melting and boiling points with the atomic number among halogens.[3]
The element is often cited to have the electronegativity of 2.2 (Pauling scale), as this is stated in Pauling's work,[5] Sony VAIO VPC-P113KX/W Battery
lower than that of iodine (2.5 in the original work and 2.66 now[6]) and same as hydrogen; the experiments have shown that the actual astatine electronegativity is slightly below that of hydrogen[7] (see below). It sublimes more readily than iodine, with lower vapor pressure; it also dissolves in water.[3] Sony VAIO VPC-P114KX/B Battery
There are 32 known isotopes of astatine, with atomic masses of of 191 and 193–223.[1] No stable or at least long-lived astatine isotope is known, and no such an isotope is expected to exist.[8]
Alpha decay energy follows the same trend as other heavy elements.[8] Lighter astatine isotopes have quite high energies of alpha decay, which get lower as the nuclei get heavier. Sony VAIO VPC-P114KX/D Battery
But astatine-211, the nucleus with 126 neutrons (126 is a magic number and corresponds to a filled neutron shell) has a significantly higher energy than the previous one. Despite having a similar half-life time with the previous isotope (8.1 hours for 210At and 7.2 hours for 211At), the alpha decay probability is way higher for the latter: 41.81% against only 0.18%.[1][note 2] Sony VAIO VPC-P114KX/G Battery
The two following isotopes release even more energy, with astatine-213 releasing the highest amount of energy of all astatine isotopes. For this reason, it is the shortest-lived astatine isotope.[8] Even though heavier astatine isotopes release less energy, no long-lived astatine isotope exists; this happens due to increasing role of beta decay.[8] Sony VAIO VPC-P114KX/P Battery
This decay mode is especially important for astatine: as early as 1950, it has been postulated that the element has no beta-stable isotopes (i.e. those that do not beta decay at all).[9] The mode has already been found for all astatine isotopes, except for 213At, 214At, 215At, 216mAt, and 217At.[1] Sony VAIO VPC-P114KX/W Battery
The most stable of them is astatine-210, which (as it has been mentioned) has a half-life of 8.1 hours. This isotope's primary decay mode is beta decay to a relatively long-lived (compared to astatine isotopes) alpha emitter, polonium-210. In total, only five isotopes have half-lives exceeding one hour, namely those with mass numbers between 207 and 211. Sony VAIO VPCP115JC Battery
The least stable ground state isotope is astatine-213, with a half-life of 125 ns. It alpha decays to the extremely long-lived (in practice, stable) bismuth-209.[1]
In nature, six astatine isotopes are present: astatine-214 to -219; they decay rapidly by primarily alpha decay, but are rapidly recreated by the decay of heavier elements as well. Sony VAIO VPCP115JC/B Battery
Astatine-215, -217, -218, and -219 are present in the major decay chains,[10]while astatine-214 and -216 (as well as astatine-215) occur as result of decay of natural protactinium.[8]
Astatine has 23 nuclear isomers (nuclei with of one or more nucleons (protons or neutrons) excited. Sony VAIO VPCP115JC/D Battery
A nuclear isomer may also be called a "meta state," which means the system has more internal energy than the "ground state" (the state with the lowest possible internal energy), making the former likely to decay into it, not always one isomer for one isotope. The most stable of them is astatine-202m1, which has a half-life of about 3 minutes; Sony VAIO VPCP115JC/G Battery
this is longer than those of all ground states, except for isotopes with mass numbers 203–211 and 220. The least stable one is astatine-214m1; its half-life of 265 ns is shorter than those of all ground states, except for astatine-213.[1]
In 1869, Dmitri Mendeleev published his periodic table. The space under iodine was empty; Sony VAIO VPCP115JC/P Battery
after Niels Bohr established the physical basis of the classification of chemical elements, it was suggested that there could be the fifth halogen. Before officially recognized discovery, it was called "eka-iodine," from Sanskrit eka, "one," to imply it was one space under iodine (in the same manner as eka-silicon, eka-boron, and others).[11] Scientists tried to find it in nature, which led to erroneous discoveries.[12] Sony VAIO VPCP115JC/W Battery
The first claimed discovery of eka-iodine was made by Fred Allison and associates at the Alabama Polytechnic Institute (now Auburn University) in 1931; the discoverers named element 85 "alabamine" and assigned it the symbol Ab, which were used for a few years.[13][14][15] Sony VAIO VPCP115KG Battery
In 1934, however, H. G. MacPherson of University of California, Berkeleydisproved the effectiveness of Allison's device and the validity of this discovery.[16] This erroneous discovery was followed by another claim in 1937, by the chemist Rajendralal De. Working in Dhaka, British India (now Bangladesh), he chose the name "dakin" for element 85, which he claimed to have isolated as the thorium series equivalent of Radium F (polonium-210) in the radium series. Sony VAIO VPCP116KG Battery
The properties he reported for dakin do not correspond to those of astatine, and its identity is not known.[17]
In 1940, the Swiss chemist Walter Minder announced the discovery of element 85 as the product of the beta decay of Radium A (polonium-218), choosing the name "helvetium" (from Helvetia, "Switzerland").Sony VAIO VPC-P116KX/B Battery
However, Berta Karlik and Traude Bernert were unsuccessful in reproducing his experiments, attributing the results to contamination of his radon stream.[18] (Radon-222 is the parent isotope of polonium-218.) In 1942, Minder, in collaboration with the English scientist Alice Leigh-Smith, announced the discovery of another isotope of element 85, presumed to be the product of Thorium A (polonium-216) beta decay. Sony VAIO VPC-P116KX/D Battery
They named this substance "anglo-helvetium,"[19] but Karlik and Bernert were again unable to reproduce these results.[20]
In 1940, Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè finally isolated the element at the University of California, Berkeley. Sony VAIO VPC-P116KX/G Battery
Instead of searching for the element in nature, the scientists actually created it by bombarding bismuth with alpha particles.[21] The name "astatine" comes from the Greek word ??????? astatos, meaning "unstable," due to the created isotope's propensity for radioactive decay (later, all isotopes of the element were shown to be unstable),[21] and the ending "-ine," found in the names of the four previously discovered halogens. Sony VAIO VPC-P116KX/P Battery
Three years later, astatine was found as a product of natural decay chains by Karlik and Bernert.[22][23] Since then, astatine has been found in three out of the four natural decay chains.[24]
Natural occurrence
Astatine is the rarest naturally occurring element among those that do not belong to the transuranium elements series, with the total amount in Earth's crust estimated to be less than 28 grams (1 oz) at given time.[25] Sony VAIO VPC-P116KX/W Battery
Astatine present at the formation of the Earth has long since decayed; natural astatine at present has formed through the decay of heavier elements. Previously thought to be the rarest element occurring on the Earth, astatine has lost this status to berkelium, atoms of which can be produced by neutron capture reactions and beta decay in very highly concentrated uranium-bearing deposits.[26] Sony VAIO VPCP118JC Battery
Six astatine isotopes occur naturally: these are astatine-214 to -219.[27] Because of their short half-lives, they are found only in traceamounts.[10] Although astatine is found on the Earth, there is no data of astatine occurrence in stars.[28]
Neptunium series, showing the decay products, including astatine-217, formed from neptunium-237. Sony VAIO VPCP118JC/B Battery
Four out of these isotopes (215At, 217At, 218At, and 219At) are found there due to their production in major natural decay chains. The father isotope of astatine-219, francium-223, alpha decays with a probability of only 0.006%, making this astatine isotope extremely rare even compared to other astatine isotopes, although its half-life is the longest of the natural astatine isotopes at 56 seconds.[1] Sony VAIO VPCP118JC/P Battery
This rare isotope decays to polonium-215, which itself beta decays to astatine-215 with an even smaller probability of 0.00023%; for this reason, the Americas to a depth of sixteen kilometers (10 mi) contains only a trillion astatine-215 atoms at given time.[29] Astatine-218 is found in nature as result of polonium-218 beta decay; Sony VAIO VPCP118JC/W Battery
like francium-223 and polonium-215, decay to an astatine isotope is not the primary decay mode.[10] Therefore, most Earth's astatine is astatine-217, whose father (francium-221) decays exclusively to this nuclide; its fathers, grandfathers, so on, decay to exclusively to one exact nuclide, to make only one possible way for the starting nuclide in the neptunium series, neptunium-237, to decay to astatine-217.[10] Sony VAIO VPC-P118KX/B Battery
The other remaining isotopes (214At and 216At, as well as 215At) are found as the result of triple alpha decay of the naturally present protactinium isotopes: 226Pa, 227Pa, and 228Pa.[27] These, however, are extremely rare, so they are often even not cited as natural astatine isotopes.[3][30]
Chemical reactivity and compounds
Astatine is the least reactive of the halogens, being less reactive than iodine;[31] Sony VAIO VPC-P118KX/D Battery
however, multiple compounds of astatine have been synthesized in microscopic amounts and studied as intensively as possible before their inevitable radioactive disintegration. The reactions are normally tested with dilute solutions of astatine mixed with larger amounts of iodine. The iodine acts as a carrier, ensuring that there is sufficient material for laboratory techniques such as filtration and precipitation to work.[20][32] Sony VAIO VPC-P118KX/G Battery
The most common compound of the element is hydrogen astatide.[3] The hydrogen astatide molecule has been calculated to have a dipole moment of 0.06 debyes, with hydrogen carrying the partial negative charge. Because astatine has a lower electronegativity when compared to hydrogen (unlike the other halogens), the molecule should more properly be called astatine monohydride;[7] Sony VAIO VPC-P118KX/P Battery
this reversal of polarity partially explains its lower stability compared to the other hydrogen halides. As it is easily oxidized, it is precipitated in aqueous nitric acid/silver(I) solution, forming silver(I) astatide, AgAt.[3]
Astatine is known to react with its lighter homologues iodine, bromine, and chlorine in the vapor state; Sony VAIO VPC-P118KX/W Battery
this reaction produces diatomic interhalogen compounds, with formulas AtI, AtBr, and AtCl.[2] The first two compounds may also be produced in water: astatine reacts with iodine/iodide solution to form AtI, whereas AtBr requires, aside from astatine, a iodine/iodine monobromide/bromide solution. Sony VAIO VPCP119JC Battery
The excess of iodides or bromides may lead to AtBr?
2 and AtI?
2 ions;[2] in a chloride solution, they may turn to species like AtCl?
2 or AtBrCl? via equilibrium.[33] No report of gas phase AtCl preparation has been shown, but oxidation of the element with dichromate (in nitric acid solution) showed that adding chloride turned the astatine into a molecule, either AtCl or AtOCl; Sony VAIO VPCP119JC/BI Battery
similarly, AtOCl?
2 or AtCl?
2 may be produced.[2] In a plasma ion source mass spectrometer, similar ions [AtI]+, [AtBr]+, and [AtCl]+ have been formed by introducing vapors of the lighter halogens to the helium-filled camera where astatine is situated, supporting the existence of stable neutral molecules in the plasma ion state.[2] Sony VAIO VPCP11S1E/B Battery
No astatine fluoride has not been discovered yet, and although its synthesis is thought to be possible, it may require a liquid halogen fluoride solvent; this has already been used for characterization of radon fluorides.[2]
The lower oxidation states are the starting point for astatine–oxygen bonds:[note 3] Sony VAIO VPC-P11S1E/B Battery
treating them with an oxygen-containing oxidizer leads to the formation of astatate ions, AtO?
3.[35] Further oxidation, e.g., by hypochlorite or electrochemical oxidation, was originally thought to form unstable astatine(VII), either as perastatic acid H5AtO6 (analogous to periodic acid) or perastatate AtO?
4;[3] however, this has never been confirmed.[36] Sony VAIO VPCP11S1E/D Battery
The intermediate states coprecipitate with several silver(I), thallium(I) or caesium oxysalts to form cationic astatine.[35] Astatine may also replace a hydrogen atom in benzene to form C6H5At, which may be oxidized to C6H5AtCl2 by chlorine; by treating this compound in an alkaline solution of hypochlorite, C6H5AtO2 may be produced.[35] Sony VAIO VPC-P11S1E/D Battery
Astatine may form bonds to the other chalcogens, such as S7At+ and At(CSN)?
2 with sulfur, a coordination selenocarbamide compound with selenium, and astatine–tellurium colloid with tellurium.[37]Additionally, astatine is known to bind to nitrogen,[38] lead,[39] and boron.[40] Sony VAIO VPCP11S1E/G Battery
Production
Astatine was first produced by bombarding bismuth with energetic alpha particles; this is still the major route used to create the relatively long-lived isotopes astatine-209 through -211. Astatine is only produced in microscopic quantities, with modern techniques allowing production runs of 2 terabecquerel (about 25 ?g).[42] Sony VAIO VPC-P11S1E/G Battery
The most important isotope is now astatine-211, being the only one to find a commercial use.[43] To produce the bismuth target, the metal is sputtered on a gold, copper, or aluminum surface, to form a 50–100 milligrams per centimeter squared bismuth layer (or, alternatively, bismuth oxide is pressed into a copper plate).[44] Sony VAIO VPCP11S1E/P Battery
The target is kept under a chemically neutral nitrogenatmosphere[45] and is cooled with water to prevent the premature astatine vaporization.[44] In a particle accelerator,[46] such as a cyclotron, alpha particles are collided with bismuth. Even though bismuth is composed of only one isotope, bismuth-209, the reaction may occur in three possible ways, producing astatine-209, -210, and -211. Sony VAIO VPCP11S1E/W Battery
In order to eliminate the undesired nuclides, the maximum energy of the reaction is set to 28 MeV. The produced astatine is then easily separated, as astatine sets itself free and a stream of the element is collected as a deposit on a glass cold finger.[45]
Separation
The freshly formed astatine is separated either chemically or via distillation.[47] Sony VAIO VPC-P11S1E/W Battery
Astatine is very volatile, even though less than iodine (in acidic solutions).[note 4] Out of such solutions, the iron(II) sulfate/sulfuric acid solution seems the most promising: it may provide the distillation of 90% of the element (85% of the solution distilled).[49]
If dry distillation is used, the element (after its formation) must be separated from the target and the traces of other radioisotopes. Sony VAIO VPCP11Z9E/B Battery
The target is heated to 300–600 °C (575–1100 °F). The freshly vaporized astatine (in form of a stream) is collected as a deposit on a glass cold finger.[49] To eliminate the polonium content in astatine, it is re-distilled.
However, astatine is thought to react with bismuth to form non-volatile compounds. Sony VAIO VPCS111FM/S Battery
This is likely to cause the low astatine outcome (up to 15%).[49]. If the temperature is raised to 700–800 °C (1275–1450 °F), 80% of astatine may be distilled, which may be explained by suggesting that the non-volatile astatine compounds decompose; however, bismuth begins to vaporize as well. Mixing the methods, up to 30% of astatine may result.[49] Sony VAIO VPCS115EC Battery
Chemical routes
Astatine may be extracted from acidic aqueous solutions using organic solvents. The distribution factor varies on the solvent: the highest one is 200, found in 0.01 M nitric acid/benzene system (the second highest is 91, in 0.01 M nitric acid/tetrachloromethane system).[50] Sony VAIO VPCS115FG Battery
In general, it is similar to iodine in that it dissolves in benzene, carbon disulfide, and tetrachloromethane (therefore, they have high distribution factors in systems with water), but, unlike iodine, it cannot be extracted from alkaline solutions of organic solvents, as it reacts with bases and disproportionates.[3] Sony VAIO VPCS117GG Battery
Diatomic interhalogen molecules (with iodine and bromine) have smaller distribution factors than dihalogens (where both atoms are the same), as the former are dipoles.[50] Separation from other elements is done via extraction from hydrochloric acid/isopropyl ether solutions. Iron(III) hydroxide may be used to remove the further traces. Using 8 M HCl solutions, outcome may be as high as 90%.[50] Sony VAIO VPCS117GGB Battery
When astatine is introduced into negatively charged chloro complexes and dissolved in chloride or hydrogen chloride (at best at 5–8 M, because the complex decomposes on a lower chloride concentration), such a complex can be sorbed on a cation resin; the same is true for the astatine cation.[51] Sony VAIO VPCS118EC Battery
Such astatine is originally inserted into tellurium, which is (together with polonium impurity) later washer away with hydrochloric acid/chlorine solution. Astatine is later desorbed via chloric water. The cation resin is processed with nitric acid solution (with a small dichromate content), and the solution is introduced to it, and later to nitric acid solution (to remove the chloride ions). Thereafter, astatine is desorbed with nitric acid/dichromate solution.[52] Sony VAIO VPCS119FJ/B Battery
Astatine partially coprecipitates from weakly acidic solutions with several hydroxides, silver(I) and thallium(I) iodides, several sulfides of heavy metals, silver metal, and tellurium. This is likely to be caused by adsorbation on the surface of the precipitate.[53] The adsorbation is suppressed by increasing the acidity of the solution, washing off the precipitate with acetone, or adding iodine; the latter proves the adsorbation character of the astatine coprecipitation.[53] Sony VAIO VPCS119GC Battery
The most important such a reaction is the one with tellurium, which is catalyzed by reducers like tin dichloride; however, the reaction does not occur in alkaline solutions. The amount of astatine precipitated does not rely on tellurium amount, reaching 90% in concentrated HCl (this reaction also eliminates different impurities).[53]Astatide and astatate have been shown to coprecipitate with iodide and iodate; Sony VAIO VPCS11AFJ Battery
they, however, cannot be washed off with acetone.[54] These methods are used most typically only when astatine is the result of a different, way rarer reaction of bismuth, lead, or thorium with high-energy protons.[54] Since such reactions produces hundreds less times astatine than the one involving bismuth and alpha particles. Therefore, the method used of separation should be effective; this one has proved to be so.[54] Sony VAIO VPCS11AGJ Battery
Uses and precautions
The newly formed astatine-211 is important in prostate cancer treatment. Once produced, astatine should be used quickly, as astatine-211 decays with a half-life of 7.2 hours; this, however, is long enough to permit multi-step labeling strategies. Sony VAIO VPCS11AHJ Battery
Astatine-211 can be used for targeted alpha particle radiotherapy, since it decays either via alpha decay to bismuth-207, or via electronic capture to an extremely short-lived nuclide of polonium-211, which itself alpha decays.[55] A selection of astatine-containing organic compounds and their medical applications can be seen in the table below: Sony VAIO VPCS11AVJ Battery
Similarly to iodine, astatine is collected by the thyroid gland, even though to a lesser extent; however, it concentrates in the liver if released to the body if the form of a radiocolloid.[44] The principled behavior difference between astatine-211 and iodine-131 (a radioactive iodine isotope, also used in medicine) is that astatine does not destroy the neighboring parathyroid gland, as it does not emit beta particles: Sony VAIO VPCS11J7E/B Battery
an average alpha particle released by astatine-211 runs about 70 µm, while a beta particle emitted by iodine-131 runs about 2 mm.[44] Thanks to its short half-life and small particle run, it is preferable to be used in diagnosis of diseases (compared to iodine-131).[44] However, it attacks the thyroid gland much stronger, and the repetative injection of the nuclide caused tissue destruction in the gland, followed by dysplasia in rats and monkeys. Sony VAIO VPCS11M1E/W Battery
When lethal quantities are added, morphological changes in other tissues are not found, with the possible exception of the breasts.
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Sony VAIO VPCS11V9E Battery
Its most stable isotope, 222Rn, has a half-life of 3.8 days. Radon is one of the densest substances that remains a gas under normal conditions and is considered a health hazard due to its radioactivity. Intense radioactivity also hindered chemical studies of radon and only a few compounds are known. Sony VAIO VPCS11V9E/B Battery
Sony VAIO VPCS11X9E/B Battery
Radon is formed as part of the normal radioactive decay chain of uranium and thorium. Uranium and thorium have been around since the earth was formed and their most common isotope has a very long half-life (4.5 billion years). Uranium and thorium,radium, and thus radon, will continue to occur for millions of years at about the same concentrations as they do now.[1] Sony VAIO VPCS123FGB Battery
As the radioactive gas of radon decays, it produces new radioactive elements called radon daughters or decay products. Radon daughters are solids and stick to surfaces such as dust particles in the air. If contaminated dust is inhaled, these particles can stick to the airways of the lung and increase the risk of developing lung cancer.[2] Sony VAIO VPCS125EC Battery
Radon is responsible for the majority of the public exposure to ionizing radiation. It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics and basements. It can also be found in some spring waters and hot springs.[3] Sony VAIO VPCS128EC Battery
Epidemiological studies have shown a clear link between breathing high concentrations of radon and incidence of lung cancer. Thus, radon is considered a significant contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States. Sony VAIO VPCS129GC Battery
About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA estimates. [4]
Physical properties
Radon is a colorless and odorless gas, and therefore not detectable by human senses alone. Sony VAIO VPCS12C7E/B Battery
At standard temperature and pressure, radon forms a monatomic gas with a density of 9.73 kg/m3,[5] about 8 times the density of the Earth's atmosphere at sea level, 1.217 kg/m3.[6] Radon is one of the heaviest gases at room temperature and is the heaviest of the noble gases. Although colorless at standard temperature and pressure, when cooled below its freezing point of 202 K (?71 °C; ?96 °F), Sony VAIO VPCS12L9E/B Battery
radon has a brilliant phosphorescence which turns from yellow to orange-red as the temperature is lowered.[7] Uponcondensation, radon glows because of the intense radiation it produces.[8]
Chemical properties
Being a noble gas, radon is chemically not very reactive. However, the 3.8 day half-life of radon-222 makes it useful in physical sciences as a natural tracer. Sony VAIO VPCS12V9E/B Battery
Radon is a member of the zero-valence elements that are called noble gases. It is inert to most common chemical reactions, such as combustion, because the outer valence shellcontains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound.[9] 1037 kJ/mol is required to extract one electron from its shells (also known as the first ionization energy).[10] Sony VAIO VPCW111XX/P Battery
However, in accordance with periodic trends, radon has a lower electronegativity than the element one period before it, xenon, and is therefore more reactive. Radon is sparingly soluble in water, but more soluble than lighter noble gases. Radon is appreciably more soluble in organic liquids than in water. Sony VAIO VPCW111XX/PC Battery
Early studies concluded that the stability of radon hydrateshould be of the same order as that of the hydrates of chlorine (Cl2) or sulfur dioxide (SO2), and significantly higher than the stability of the hydrate of hydrogen sulfide (H2S).[11]
Because of its cost and radioactivity, experimental chemical research is seldom performed with radon, and as a result there are very few reported compounds of radon, Sony VAIO VPCW111XX/T Battery
all eitherfluorides or oxides. Radon can be oxidized by a few powerful oxidizing agents such asfluorine, thus forming radon fluoride.[12][13] It decomposes back to elements at a temperature of above 250 °C. It has a low volatility and was thought to be RnF2. But because of the short half-life of radon and the radioactivity of its compounds, it has not been possible to study the compound in any detail. Sony VAIO VPCW111XX/W Battery
Theoretical studies on this molecule predict that it should have a Rn-Fbond distance of 2.08 ?, and that the compound is thermodynamically more stable and less volatile than its lighter counterpart XeF2.[14]The octahedral molecule RnF6 was predicted to have an even lower enthalpy of formation than the difluoride.[15] The [RnF]+ ion is believed to form by the reaction:[16] Sony VAIO VPCW111XXP Battery
Rn (g) + 2 [O2]+[SbF6]? (s) ? [RnF]+[Sb2F11]? (s) + 2 O2 (g)
Radon oxides are among the few other reported compounds of radon.[17] Radon carbonyl RnCO has been predicted to be stable and to have a linear molecular geometry.[18] The molecules Rn2 and RnXe were found to be significantly stabilized by spin-orbit coupling.[19] Radon caged inside a fullerene has been proposed as a drug for tumors.[20] Sony VAIO VPCW111XXT Battery
Radon has no stable isotopes. However, 36 radioactive isotopes have been characterized, with their atomic masses ranging from 193 to 228.[21] The most stable isotope is 222Rn, which is a decay product of 226Ra, a decay product of 238U.[22] Among the daughters of 222Rn is also the highly unstable isotope 218Rn. Sony VAIO VPCW111XXW Battery
There are three other radon isotopes that have a half-life of over an hour: 211Rn, 210Rn and 224Rn. The 220Rn isotope is a natural decay product of the most stable thorium isotope (232Th), and is commonly referred to as thoron. It has a half-life of 55.6 seconds and also emits alpha radiation. Sony VAIO VPCW115XG Battery
Similarly, 219Rn is derived from the most stable isotope of actinium (227Ac)—named "actinon"—and is an alpha emitter with a half-life of 3.96 seconds.[21] No radon isotopes significantly occur in the neptunium(237Np) decay series. Sony VAIO VPCW115XGP Battery
Progenies
222Rn belongs to the radium and uranium-238 decay chain, and has a half-life of 3.8235 days. Its four first products (excluding marginal decay schemes) are very short-lived, meaning that the corresponding disintegrations are indicative of the initial radon distribution. Its decay goes through the following sequence:[21] Sony VAIO VPCW115XW/P Battery
- 222Rn, 3.8 days, alpha decaying to...
- 218Po, 3.10 minutes, alpha decaying to...
- 214Pb, 26.8 minutes, beta decaying to...
- 214Bi, 19.9 minutes, beta decaying to...
- 214Po, 0.1643 ms, alpha decaying to...
At the next step, 214Po decays to 210Pb, which has a much longer half-life of 22.3 years. Its progenies are: Sony VAIO VPCW115XW/T Battery
- 210Bi, 5.013 days, beta decaying to...
- 210Po, 138.376 days, alpha decaying to...
- 206Pb, stable.
The radon equilibrium factor[23] is the ratio between the activity of all short-period radon progenies (which are responsible for most of radon's biological effects), and the activity that would be at equilibrium with the radon parent. Sony VAIO VPCW115XW/W Battery
If a closed volume is constantly supplied with radon, the concentration of short-lived isotopes will increase until an equilibrium is reached where the rate of decay of each decay product will equal that of the radon itself. The equilibrium factor is 1 when both activities are equal, meaning that the decay products have stayed close to the radon parent long enough for the equilibrium to be reached, within a couple of hours. Sony VAIO VPCW117XC/P Battery
Under these conditions each additional pCi/L of radon will increase exposure, by 0.01 WL (see explanation of WL below). These conditions are not always met: in many homes, the equilibrium fraction is typically 40%; that is, there will be 0.004 WL of progeny for each pCi/L of radon in air.[24] 210Pb takes much longer (decades) to come in equilibrium with radon, but, if the environment permits accumulation of dust over extended periods of time, 210lead and its decay products may contribute to overall radiation levels as well. Sony VAIO VPCW117XC/T Battery
Because of their electrostatic charge, radon progenies adhere to surfaces or dust particles, whereas gaseous radon does not. Attachment removes them from the air, usually causing the equilibrium factor in the atmosphere to be less than one. The equilibrium factor is also lowered by air circulation or air filtration devices, and is increased by airborne dust particles, including cigarette smoke. Sony VAIO VPCW117XC/W Battery
In high concentrations, airborne radon isotopes contribute significantly to human health risk. The equilibrium factor found in epidemiological studies is 0.4.[25]
History and etymology
Radon was the fifth radioactive element to be discovered, in 1900 by Friedrich Ernst Dorn, after uranium, thorium, radium and polonium.[26][27][28] Sony VAIO VPCW119XJ Battery
In 1900 Dorn reported some experiments in which he noticed that radium compounds emanate a radioactive gas which he named Radium Emanation (Ra Em).[29] Before that, in 1899, Pierre and Marie Curie observed that the "gas" emitted by radium remained radioactive for a month.[30] Later that year, Robert B. Owens and Ernest Rutherford, Sony VAIO VPCW119XJ/P Battery
at McGill Universityin Montreal, noticed variations when trying to measure radiation from thorium oxide.[31] Rutherford noticed that the compounds of thorium continuously emit a radioactive gas which retain the radioactive powers for several minutes and called this gas "emanation" (from Latin "emanare"—to elapse and "emanatio"—expiration),[32] and later Thorium Emanation (Th Em). Sony VAIO VPCW119XJ/W Battery
In 1901, he demonstrated that the emanations are radioactive, but credited the Curies for the discovery of the element.[33] In 1903, similar emanations were observed from actinium by André-Louis Debierne[34][35] and were called Actinium Emanation (Ac Em).
Several names were suggested for these three gases: exradio, exthorio, and exactinio in 1904;[36] radon, thoron, and akton in 1918;[ Sony VAIO VPCW11AXJ Battery
37]radeon, thoreon, and actineon in 1919,[38] and eventually radon, thoron, and actinon in 1920.[39] The likeness of the spectra of these three gases with those of argon, krypton, and xenon, and their observed chemical inertia led Sir William Ramsay to suggest in 1904 that the "emanations" might contain a new element of the noble gas family.[36] Sony VAIO VPCW11S1E/P Battery
In 1910, Sir William Ramsay and Robert Whytlaw-Gray isolated radon, determined its density, and determined that it was the heaviest known gas.[40] They wrote that "L'expression de l'émanation du radium est fort incommode," (the expression of radium emanation is very awkward) and suggested the new name niton (Nt) Sony VAIO VPCW11S1E/T Battery
(from the Latin "nitens" meaning "shining") in order to emphasize the property of gases that cause the phosphorescence of some substances,[40] and in 1912 it was accepted by the International Commission for Atomic Weights. In 1923, the International Committee for Chemical Elements and International Union of Pure and Applied Chemistry (IUPAC) chose among the names radon (Rn), thoron (Tn), and actinon (An). Sony VAIO VPCW11S1E/W Battery
Later, when isotopes were numbered instead of named, the element took the name of the most stable isotope, radon, while Tn was renamed 220Rn and An was renamed 219Rn. As late as the 1960s, the element was also referred to simply as emanation.[41] The first synthesized compound of radon, radon fluoride, was obtained in 1962.[42] Sony VAIO VPCW121AX Battery
The danger of high exposure to radon in mines, where exposures reaching 1,000,000 Bq/m3 can be found, has long been known. In 1530,Paracelsus described a wasting disease of miners, the mala metallorum, and Georg Agricola recommended ventilation in mines to avoid this mountain sickness (Bergsucht).[43][44] In 1879, this condition was identified as lung cancer by Herting and Hesse in their investigation of miners from Schneeberg, Germany. Sony VAIO VPCW126AG Battery
The first major studies with radon and health occurred in the context of uranium mining in theJoachimsthal region of Bohemia.[45] In the US, studies and mitigation only followed decades of health effects on uranium miners of theSouthwestern United States employed during the early Cold War; standards were not implemented until 1971.[46] Sony VAIO VPCW127JC/P Battery
The presence of radon in indoor air was documented as early as 1950. Beginning in the 1970’s research was initiated to address sources of indoor radon, determinants of concentration, health effects, and approaches to mitigation. In the United States, the problem of indoor radon received widespread publicity and intensified investigation after a widely publicized incident in 1984. Sony VAIO VPCW127JC/T Battery
During routine monitoring at a Pennsylvania nuclear power plant, a worker was found to be contaminated with radioactivity. A high contamination of radon in his home was subsequently identified as responsible for the contamination.[47]
Concentration units
All discussions of radon concentrations in the environment refer to 222Rn. Sony VAIO VPCW127JC/W Battery
While the average rate of production of220Rn (from the thorium decay series) is about the same as 222Rn, the amount of 220Rn in the environment is much less than that of 222Rn because of the short half-life of 220Rn (1 minute versus 4 days).[1]
Radon concentration is usually measured in the atmosphere, in becquerel per cubic meter (Bq/m3), the SI derived unit. Sony VAIO VPCW127JC/WZ Battery
Typical domestic exposures are about 100 Bq/m3 indoors, and 10–20 Bq/m3 outdoors.[citation needed]
It is often measured in picocuries per liter (pCi/L) in the USA, with 1 pCi/L=37 Bq/m3.[24]
In the mining industry, the exposition is traditionally measured in working level (WL), and the cumulative exposition in working level month (WLM): Sony VAIO VPCW12AAJ Battery
1 WL equals any combination of short-lived 222Rn progeny (218Po, 214Pb, 214Bi, and 214Po) in 1 liter of air that releases 1.3 × 105 MeV of potential alpha energy;[24] one WL is equivalent to 2.08 × 10?5joules per cubic meter of air (J/m3).[1] The SI unit of cumulative exposure is expressed in joule-hours per cubic meter (J·h/m3). One WLM is equivalent to 3.6 × 10?3 J·h/m3. Sony VAIO VPCW12AKJ Battery
An exposure to 1 WL for 1 working month (170 hours) equals 1 WLM cumulative exposure.[citation needed]
A cumulative exposition of 1 WLM is roughly equivalent to living one year in an atmosphere with a radon concentration of 230 Bq/m3.[49]
Radon (222Rn), when released into the air, decays to 210Pb and other radioisotopes, the levels of 210Pb can be measured. The rate of deposition of this radioisotope is weather dependent. Sony VAIO VPCW12AVJ Battery
Radon concentrations found in natural environments are much too low to be detected by chemical means. A 1000 Bq/m3 (relatively high) concentration corresponds to 0.17 picogram per cubic meter. The average concentration of radon in the atmosphere is about 6×10?20 atoms of radon for each molecule in the air, or about 150 atoms in each ml of air.[50] Sony VAIO VPCW12S1E/P Battery
The radon activity of the Earth atmosphere originates from some tens of grams of radon, consistently replaced by decay of larger amounts of radium and uranium.[51]
Natural
Radon is produced by the radioactive decay of radium-226, which is found in uranium ores; phosphate rock; shales; metamorphic minerals such as granite, gneiss, and schist; Sony VAIO VPCW12S1E/T Battery
and, to a lesser degree, in common minerals such as limestone.[52] Every square mile of surface soil, to a depth of 6 inches (2.6 km2 to a depth of 15 cm), contains approximately 1 gram of radium, which releases radon in small amounts to the atmosphere[1] On a global scale, it is estimated that 2,400 million curies (90 TBq) of radon are released from soil annually.[53] Sony VAIO VPCW12S1E/W Battery
Radon concentration varies widely from place to place. In the open air, it ranges from 1 to 100 Bq/m3, even less (0.1 Bq/m3) above the ocean. In caves or aerated mines, or ill-aerated houses, its concentration climbs to 20–2,000 Bq/m3.[54] Radon concentration can be much higher in mining contexts. Ventilation regulations instruct to maintain radon concentration in uranium mines under the "working level", Sony VAIO VPCW213AG/L Battery
with 95th percentile levels ranging up to nearly 3 WL (546 pCi 222Rn per liter of air; 20.2 kBq/m3, measured from 1976 to 1985).[1] The concentration in the air at the (unventilated) Gastein Healing Gallery averages 43 kBq/m3 (1.2 nCi/L) with maximal value of 160 kBq/m3 (4.3 nCi/L).[55] Sony VAIO VPCW213AG/P Battery
Radon mostly appears with the decay chain of the radium and uranium series (222Rn), and marginally with the thorium series (220Rn). The element emanates naturally from the ground, and some building materials, all over the world, wherever traces of uranium orthorium can be found, and particularly in regions with soils containing granite or shale, which have a higher concentration of uranium. Sony VAIO VPCW213AG/T Battery
However, not all granitic regions are prone to high emissions of radon. Being a rare gas, it usually migrates freely through faults and fragmented soils, and may accumulate in caves or water. Owing to its very short half-life (four days for 222Rn), radon concentration decreases very quickly when the distance from the production area increases. Radon concentration varies greatly with season and atmospheric conditions. Sony VAIO VPCW213AG/W Battery
For instance, it has been shown to accumulate in the air if there is a meteorological inversion and little wind.[56]
High concentrations of radon can be found in some spring waters and hot springs.[57] The towns of Boulder, Montana; Misasa; Bad Kreuznach, Germany; and the country of Japan have radium-rich springs which emit radon. Sony VAIO VPCW215AG/L Battery
To be classified as a radon mineral water, radon concentration must be above a minimum of 2 nCi/L (74 kBq/m3).[58] The activity of radon mineral water reaches 2,000 kBq/m3 in Merano and 4,000 kBq/m3 in Lurisia (Italy).[55]
Natural radon concentrations in Earth's atmosphere are so low that radon-rich water in contact with the atmosphere will continually lose radon by volatilization. Sony VAIO VPCW217JC Battery
Hence, ground water has a higher concentration of 222Rn than surface water, because radon is continuously produced by radioactive decay of 226Ra present in rocks. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone because of diffusional losses to the atmosphere.[59][60] Sony VAIO VPCW217JC/L Battery
In 1971, Apollo 15 passed 110 km (68 mi) above the Aristarchus plateau on the Moon, and detected a significant rise in alpha particles thought to be caused by the decay of 222Rn. The presence of 222Rn has been inferred later from data obtained from the Lunar Prospector alpha particle spectrometer.[61] Sony VAIO VPCW217JC/P Battery
Radon is found in some petroleum. Because radon has a similar pressure and temperature curve to propane, and oil refineriesseparate petrochemicals based on their boiling points, the piping carrying freshly separated propane in oil refineries can become radioactive because of decaying radon and its products.[62] Sony VAIO VPCW217JC/T Battery
Residues from the petroleum and natural gas industry often contain radium and its daughters. The sulfate scale from an oil well can be radium rich, while the water, oil, and gas from a well often contains radon. Radon decays to form solid radioisotopes which form coatings on the inside of pipework. [62] Sony VAIO VPCW217JC/W Battery
Accumulation in houses
The phenomenon of heightened radon contamination in homes was discovered by chance in 1985 after the stringent radiation testing conducted at a nuclear power plant entrance revealed that Stanley Watras, an engineer entering the plant, was contaminated by radioactive substances.[63] Sony VAIO VPCW218JC Battery
Typical domestic exposures are of approximately 100 Bq/m3indoors. Depending on how houses are built and ventilated, radon may accumulate in basements and dwellings. Radon can also seep into an indoor environment through cracks in solid floors, construction joints, cracks in walls, gaps in suspended floors, gaps around service pipes, cavities inside walls, and the water supply.[64] Sony VAIO VPCW218JC/L Battery
Radon concentrations in the same location may differ by a factor of two over a period of 1 hour. Also, the concentration in one room of a building may be significantly different than the concentration in an adjoining room.[1]
The distribution of radon concentrations tends to be asymmetrical around the average, the larger concentrations have a disproportionately greater weight. Sony VAIO VPCW218JC/P Battery
Indoor radon concentration is usually assumed to follow a lognormal distribution on a given territory.[65] Thus, the geometric mean is generally used for estimating the "average" radon concentration in an area.[66] The mean concentration ranges from less than 10 Bq/m3 to over 100 Bq/m3 in some European countries.[67] Sony VAIO VPCW218JC/T Battery
Typical geometric standard deviations found in studies range between 2 and 3, meaning (given the 68-95-99.7 rule) that the radon concentration is expected to be more than a hundred times the mean concentration for 2 to 3% of the cases.
The highest average radon concentrations in the United States are found in Iowa and in the Appalachian Mountain areas in southeastern Pennsylvania.[68] Sony VAIO VPCW218JC/W Battery
Some of the highest readings ever have been recorded in the Irish town of Mallow, County Cork, prompting local fears regarding lung cancer. Iowa has the highest average radon concentrations in the United States due to significant glaciation that ground the granitic rocks from the Canadian Shield and deposited it as soils making up the rich Iowa farmland.[69] Sony VAIO VPCW219AJ/L Battery
Many cities within the state, such as Iowa City, have passed requirements for radon-resistant construction in new homes. In a few locations,uranium tailings have been used for landfills and were subsequently built on, resulting in possible increased exposure to radon.[1]
Industrial production
Radon is obtained as a by-product of uraniferous ores processing after transferring into 1% solutions of hydrochloricor hydrobromic acids. Sony VAIO VPCW219AJ/P Battery
The gas mixture extracted from the solutions contains H2, O2, He, Rn, CO2, H2O and hydrocarbons. The mixture is purified by passing it over copper at 720 °C to remove the H2 and the O2, and then KOH and P2O5 are used to remove the acids and moisture by sorption. Radon is condensed by liquid nitrogen and purified from residue gases by sublimation.[70] Sony VAIO VPCW219AJ/W Battery
Radon commercialization is regulated, but it is available in small quantities for the calibration of 222Rn measurement systems, at a price of almost $6,000 per milliliter of radium solution (which only contains about 15 picograms of actual radon at a given moment).[71] Radon is produced by a solution of radium-226 (half-life of 1600 years). Sony VAIO VPCW21AAJ Battery
Radium-226 decays by alpha-particle emission, producing radon which collects over samples of radium-226 at a rate of about 1 mm3/day per gram of radium; equilibrium is quickly achieved and radon is produced in a steady flow, with an activity equal to that of the radium (50 Bq). Gaseous 222Rn (half-life of about four days) escapes from the capsule through diffusion.[72] Sony VAIO VPCW21AKJ Battery
An early-20th-century form of quackery was the treatment of maladies in a radiotorium.[73] It was a small, sealed room for patients to be exposed to radon for its "medicinal effects". The carcinogenic nature of radon due to its ionizing radiation became apparent later on. Radon's molecule-damaging radioactivity has been used to kill cancerous cells.[74] Sony VAIO VPCW21AVJ Battery
It does not, however, increase the health of healthy cells. In fact, the ionizing radiation causes the formation of free radicals, which results in genetic and other cell damage, resulting in increased rates of illness, including cancer.
Exposure to radon, a process known as radiation hormesis, has been suggested to mitigate auto-immune diseases such asarthritis.[75][76] Sony VAIO VPCY115FGS Battery
As a result, in the late 20th century and early 21st century, some "health mines" were established in Basin, Montana which attracted people seeking relief from health problems such as arthritis through limited exposure to radioactive mine water and radon. However, the practice is discouraged because of the well-documented ill effects of high-doses of radiation on the body.[77] Sony VAIO VPCY115FX/BI Battery
Radioactive water baths have been applied since 1906 in Jáchymov, Czech Republic, but even before radon discovery they were used in Bad Gastein, Austria. Radium-rich springs are also used in traditional Japanese onsen in Misasa, Tottori Prefecture. Drinking therapy is applied in Bad Brambach, Germany. Inhalation therapy is carried out in Gasteiner-Heilstollen, Sony VAIO VPCY115FXBI Battery
Austria, in ?wieradów-Zdrój, Czerniawa-Zdrój, Kowary, L?dek Zdrój, Poland, in Harghita B?i, Romania, and in Boulder, United States. In the United States and Europe there are several "radon spas," where people sit for minutes or hours in a high-radon atmosphere in the belief that low doses of radiation will invigorate or energize them.[76][78] Sony VAIO VPCY118EC Battery
Radon has been produced commercially for use in radiation therapy, but for the most part has been replaced by radionuclides made in accelerators and nuclear reactors. Radon has been used in implantable seeds, made of gold or glass, primarily used to treat cancers. The gold seeds were produced by filling a long tube with radon pumped from a radium source, the tube being then divided into short sections by crimping and cutting. Sony VAIO VPCY118GX/BI Battery
The gold layer keeps the radon within, and filters out the alpha and beta radiations, while allowing the gamma rays to escape (which kill the diseased tissue). The activities might range from 0.05 to 5 millicuries per seed (2 to 200 MBq).[74] The gamma rays are produced by radon and the first short-lived elements of its decay chain (218Po, 214Pb, 214Bi, 214Po). Sony VAIO VPCY119FJ/S Battery
Radon and its first decay products being very short-lived, the seed is left in place. After 12 half-lives (43 days), radon radioactivity is at 1/2000 of its original level. At this stage, the predominant residual activity originates from the radon decay product 210Pb, whose half-life (22.3 years) is 2000 times that or radon (and whose activity is thus 1/2000 of radon's), and its descendants 210Bi and 210Po, totalizing 0.03% of the initial seed activity. Sony VAIO VPCY11AFJ Battery
In the early part of the 20th century in the USA, gold which was contaminated with 210Pb entered the jewelry industry. This was from gold seeds which had held 222Rn that had been melted down after the radon had decayed.[79][80] Wearing a contaminated ring could lead to a skin exposition of 10 to 100 rad/day (0.4 to 4 mSv/h)[81] Sony VAIO VPCY11AGJ Battery
Scientific
Radon emanation from the soil varies with soil type and with surface uranium content, so outdoor radon concentrations can be used to track air masses to a limited degree. This fact has been put to use by some atmospheric scientists. Sony VAIO VPCY11AHJ Battery
Because of radon's rapid loss to air and comparatively rapid decay, radon is used in hydrologic research that studies the interaction between ground water and streams. Any significant concentration of radon in a stream is a good indicator that there are local inputs of ground water. Radon is also used in the dating of oil-containing soils because radon has a high affinity for oil-like substances. Sony VAIO VPCY11AVJ Battery
Radon soil-concentration has been used in an experimental way to map buried close-subsurface geological faults because concentrations are generally higher over the faults.[82] Similarly, it has found some limited use in prospecting for geothermal gradients.
Some researchers have investigated changes in groundwater radon concentrations for earthquake prediction. Sony VAIO VPCY11M1E/S Battery
Radon has a half-life of approximately 3.8 days, which means that it can be found only shortly after it has been produced in the radioactive decay chain. For this reason, it has been hypothesized that increases in radon concentration is due to the generation of new cracks underground, which would allow increased ground water circulation, flushing out radon. Sony VAIO VPCY11S1E Battery
The generation of new cracks might not unreasonably be assumed to precede major earthquakes. In the 1970s and 1980s, scientific measurements of radon emissions near faults found that earthquakes often occurred with no radon signal, and radon was often detected with no earthquake to follow. It was then dismissed by many as an unreliable indicator.[86] Sony VAIO VPCY11V9E/S Battery
However, as of 2009, it is under investigation as a possible precursor by NASA.[87]
Radon is a known pollutant emitted from geothermal power stations, though it disperses rapidly, and no radiological hazard has been demonstrated in various investigations. The trend in geothermal plants is to reinject all emissions by pumping deep underground, and this seems likely to ultimately decrease such radon hazards further. Sony VAIO VPCY218EC/BI Battery
In the 1950s, radon has been used in industrial radiography.[88]
Relative risk of lung cancer mortality by cumulative exposure to radon decay products (in WLM) from the combined data from 11 cohorts of underground hard rock miners. Though high exposures (>50 WLM) cause statistically significant excess cancers, the case of small exposures (10 WLM) is inconclusive and appears slightly beneficial in this study. Sony VAIO VPCY218EC/G Battery
Radon-222 has been classified by International Agency for Research on Cancer as being carcinogenic to humans,[89] and as a gas that can be inhaled, lung cancer is a particular concern for people exposed to high levels of radon for sustained periods of time. During the 1940s and 50s, when safety standards requiring expensive ventilation in mines were not widely implemented,[90] Sony VAIO VPCY218EC/L Battery
radon exposure was linked to lung cancer among non-smoking miners of uranium and other hard rock materials in what is now theCzech Republic, and later among miners from the Southwestern United States.[91][92][93]
Since that time, ventilation and other measures have been used to reduce radon levels in most affected mines that continue to operate. Sony VAIO VPCY218EC/P Battery
In recent years, the average annual exposure of uranium miners has fallen to levels similar to the concentrations inhaled in some homes. This has reduced the risk of occupationally induced cancer from radon, although health issues may persist for those who are currently employed in affected mines and for those who have been employed in them in the past.[94] As the relative risk for miners has decreased, so has the ability to detect excess risks among that population.[95] Sony VAIO VPCY21S1E/L Battery
Radon exposure (actually radon progeny) has been linked to lung cancer in numerous case-control studies performed in the United States, Europe and China. There are approximately 21,000 deaths per year in the USA due to radon-induced lung cancers.[96]
One of the most comprehensive radon studies performed in the United States by Dr. R. Sony VAIO VPCY21S1E/P Battery
William Field and colleagues found a 50% increased lung cancer risk even at the protracted exposures at the EPA's action level of 4 pCi/L. North American and European Pooled analyses further support these findings.[97] Many researchers have highlighted a theoretical possible increased risk ofleukemia of radon, but empirical support for this has not emerged.[98][99] Sony VAIO VPCY21S1E/SI Battery
The effects of radon if ingested are similarly unknown, although studies have found that its biological half-life ranges from 30–70 minutes, with 90 percent removal at 100 minutes. In 1999 National Research Council investigated the issue of radon in drinking water. The risks associated with ingestion was considered almost negligible.[100] Sony VAIO VPCZ110 Battery
As well as being ingested through drinking water, radon is also released from water when temperature is increased, pressure is decreased and when water is aerated. Optimum conditions for radon release and exposure occur during showering. Water with a radon concentration of 10 4 pCi/L can increase the indoor airborne radon concentration by 1 pCi/L under normal conditions of water use.[101] Sony VAIO VPCZ110GB/BI Battery
Domestic-level exposure
A controversial epidemiological study showing decreased cancer risk vs. radon domestic exposure (5 pCi/L ? 200 Bq/m3).[102]This study lacks individual level controls for smoking and radon exposure, and therefore lacks statistical power to draw conclusions on what would beradiation hormesis. Sony VAIO VPCZ112GD/S Battery
Because of this the error bars (which simply reflect the raw data variability) are probably too small.[103]
Most models of residential radon exposure are based on studies of miners, and direct estimates of the risks posed to homeowners would be more desirable.[94] Nonetheless, because of the difficulties of measuring the risk of radon relative to other contributors—namely smoking—models of their effect have often made use of them. Sony VAIO VPCZ112GX/S Battery
Radon has been considered the second leading cause of lung cancer and leading environmental cause of cancer mortality by theUnited States Environmental Protection Agency.[104] Others have reached similar conclusions for the United Kingdom [94] and France.[105] Radon exposure in homes and offices may arise from certain subsurface rock formations and also from certain building materials (e.g. some granites); Sony VAIO VPCZ114GX/S Battery
greatest risk of radon exposure arises from buildings which are tight, insufficiently ventilated and have leaks that let in soil air from the ground into basements and dwelling rooms.
The actionable concentration of radon in a home varies depending on the organization doing the recommendation, for example, Sony VAIO VPCZ115 Battery
the United States Environmental Protection Agency encourages that action be taken at concentrations as low as 74 Bq/m3(2 pCi/L),[106]and the European Union recommends action be taken when concentrations reach 400 Bq/m3 (11 pCi/L) for old houses and 200 Bq/m3(5 pCi/L) for new ones.[citation needed]
On 8 July 2010 the UK's Health Protection Agency issued new advice setting a "Target Level" of 100 Bq/m3 whilst retaining an "Action Level" of 200 Bq/m3.[107] Sony VAIO VPCZ115FC/B Battery
Radon and smoking
Results from epidemiological studies indicate that the risk of lung cancer increases with exposure to residential radon. However, there are always major uncertainties in these studies. A classical and well-known example of source of error is smoking. Sony VAIO VPCZ115FC/S Battery
In addition, smoking is the most important risk factor for lung cancer. In the West, tobacco smoke is estimated to cause about 90% of all lung cancers. There is a tendency for other hypothetical lung cancer risks to drown in the risk of smoking. Results from epidemiological studies must always be interpreted with caution. Sony VAIO VPCZ116 Battery
According to the EPA, the risk of lung cancer for smokers is significant due to synergistic effects of radon and smoking. For this population about 62 people in a total of 1,000 will die of lung cancer compared to 7 people in a total of 1,000 for people who have never smoked.[96]
Radon, like other known or suspected external risk factors for lung cancer, is a threat for smokers and former smokers. Sony VAIO VPCZ116GX/S Battery
This was clearly demonstrated by the European pooling study.[108] A commentary[109] to the pooling study stated: "it is not appropriate to talk simply of a risk from radon in homes. The risk is from smoking, compounded by a synergistic effect of radon for smokers. Without smoking, the effect seems to be so small as to be insignificant." Sony VAIO VPCZ117 Battery
A study[110] of radiation from postmastectomy radiotherapy shows that the simple models previously used to assess the combined and separate risks from radiation and smoking need to be developed. This is also supported by new discussion about the calculation method, LNT, which routinely has been used.[111] Sony VAIO VPCZ117FC/B Battery
Radon and passive smoking
An important question is if also passive smoking can cause a similar synergy effect with residential radon. This has been insufficiently studied. The basic data for the European pooling study makes it impossible to exclude that such synergy effect is an explanation for the (very limited) increase in the risk from radon that was stated for non-smokers. Sony VAIO VPCZ118 Battery
A study[112] from 2001 which included 436 cases (never smokers who had lung cancer), and a control group (1649 never smokers) showed that exposure to radon increased the risk of lung cancer in never smokers. But the group that had been exposed to passive smoking at home appeared to bear the entire risk increase, while those who were not exposed to passive smoking did not show any increased risk with increasing radon level. Sony VAIO VPCZ118GC/B Battery
This result needs confirmation by additional studies. Despite the startling results from 2001, new studies seem not to have been implemented.
Testing and mitigation
There are relatively simple tests for radon gas, but these tests are not commonly done, even in areas of known systematic hazards. Radon test kits are commercially available. Sony VAIO VPCZ118GX/S Battery
The short-term radon test kits used for screening purposes are inexpensive, in many cases free. The kit includes a collector that the user hangs in the lowest livable floor of the house for 2 to 7 days. The user then sends the collector to a laboratory for analysis. Long term kits, taking collections for up to one year, are also available. An open-land test kit can test radon emissions from the land before construction begins.[4] Sony VAIO VPCZ119 Battery
Radon levels fluctuate naturally, due to factors like transient weather conditions, so an initial test might not be an accurate assessment of a home's average radon level. Radon levels are at a maximum during the coolest part of the day when pressure differentials are greatest.[113] Therefore, a high result (over 4 pCi/L) justifies repeating the test before undertaking more expensive abatement projects. Sony VAIO VPCZ119FJ/S Battery
Measurements between 4 and 10 pCi/L warrant a long term radon test. Measurements over 10 pCi/L warrant only another short term test so that abatement measures are not unduly delayed. Purchasers of real estate are advised to delay or decline a purchase if the seller has not successfully abated radon to 4 pCi/L or less.[4] Sony VAIO VPCZ119GC/X Battery
Because the half-life of radon is only 3.8 days, removing or isolating the source will greatly reduce the hazard within a few weeks. Another method of reducing radon levels is to modify the building's ventilation. Generally, the indoor radon concentrations increase as ventilation rates decrease.[1] In a well ventilated place, the radon concentration tends to align with outdoor values (typically 10 Bq/m3, ranging from 1 to 100 Bq/m3).[4] Sony VAIO VPCZ119L Battery
Radon levels in indoor air can be lowered in a number of ways, from sub-slab depressurization to increasing the ventilation rate of the building. The four principal ways of reducing the amount of radon accumulating in a house are:[4][114]
Sub-slab depressurization (soil suction) by increasing under-floor ventilation; Sony VAIO VPCZ119R/B Battery
- Improving the ventilation of the house and avoiding the transport of radon from the basement into living rooms;
- Installing a radon sump system in the basement;
Installing a positive pressurization or positive supply ventilation system. Sony VAIO VPCZ119R/S Battery
According to the EPA's "A Citizen's Guide to Radon",[115] the method to reduce radon "primarily used is a vent pipe system and fan, which pulls radon from beneath the house and vents it to the outside", which is also called sub-slab depressurization, active soil depressurization, or soil suction. Sony VAIO VPCZ11AFJ Battery
Generally indoor radon can be mitigated by sub-slab depressurization and exhausting such radon-laden air to the outdoors, away from windows and other building openings. "EPA generally recommends methods which prevent the entry of radon. Soil suction, for example, prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe, or pipes, Sony VAIO VPCZ11AGJ Battery
to the air above the home where it is quickly diluted" and "EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently" according to the EPA's "Consumer's Guide to Radon Reduction: How to fix your home".[116] Sony VAIO VPCZ11AVJ Battery
Positive-pressure ventilation systems can be combined with a heat exchanger to recover energy in the process of exchanging air with the outside, and simply exhausting basement air to the outside is not necessarily a viable solution as this can actually draw radon gas into a dwelling. Sony VAIO VPCZ11CGX/X Battery
Homes built on a crawl space may benefit from a radon collector installed under a "radon barrier" (a sheet of plastic that covers the crawl space).[4][117] For crawlspaces, the EPA states "An effective method to reduce radon levels in crawlspace homes involves covering the earth floor with a high-density plastic sheet. Sony VAIO VPCZ11DGX/SJ Battery
A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called submembrane suction, and when properly applied is the most effective way to reduce radon levels in crawlspace homes." Sony VAIO VPCZ11FHX/XQ Battery,Sony VAIO VPCZ11V9R/B Battery,Sony VAIO VPCZ11X9E/B Battery,Sony VAIO VPCZ11Z9E/B Battery,Sony VAIO VPCZ125GX/S Battery
No comments:
Post a Comment