Polonium source

Indirect evidence for the existence of H2P0 has been found in measurements of ionization brought about by a radiation from Po in an H2 atmosphere. The very high increases in observed ionization which were observed (no solid window was present between the polonium source and the ionization chamber) were attributed to formation of H2P0. 

Haissinsky and Walen [35] subjected nitrogen iodide to 5-MeV a-particles from a polonium source. The dryness of the sample and the intensity of the source decreased the time to explosion. The investigators stated that "the detonation of nitrogen iodide could be explained by a local heating of a grain of the powder." However, they thought this was an exceptional result because lead azide, silver azide, and diazo-zw-nitroaniline perchlorate did not detonate from 1 mCi of Po within 20 min. In lead azide a yellowing of the material occurred. 

First he had to shift his laboratory to a different part of the Cavendish building, and that delayed him then he had to prepare a strong polonium source. In the matter of polonium he was lucky. Norman Feather had spent the 1929-30 academic year in Baltimore, in the physics department at Johns Hopkins, and there befriended an English physician who was in charge of the radium supply at Baltimore s Kelly Hospital. The physician had stored away several hundred used radon seeds together, Feather remembers, they contained almost as much polonium as was available to Curie and Joliot in Paris. The hospital donated them to the Cavendish and Feather brought them home. Chadwick accomplished the dangerous chemical separation that autumn. 

The use of the alpha-particle ion source was discontinued about two years ago. The high-pressure capability of the instrument was outweighed by several drawbacks continuous vigilance to prevent radioactive contamination was necessary the ion source temperature could not be raised above 200°C since spreading of the polonium occurred at high temperatures and the required periodic renewal of the polonium source led ultimately to high cost. 

Because almost all alpha radiation is stopped within the solid source and its container, giving up its energy, polonium has attracted attention for uses as a lightweight heat source for thermoelectric power in space satellites. 

Polonium can be mixed or alloyed with beryllium to provide a source of neutrons. The element has been used in devices for eliminating static charges in textile mills, etc. however, beta sources are both more commonly used and less dangerous. It is also used on brushes for removing dust from photographic films. The polonium for these is carefully sealed and controlled, minimizing hazards to the user. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Polonium, because of its very low abundance and very short half-life, is not obtained from natural sources. Virtually all our knowledge of the physical and chemical properties of the element come from studies on Po which is best made by neutron irradiation of in a nuclear reactor ... 

Polonium is a radioactive, low-melting metalloid. It is a useful source of a particles (helium-4 nuclei they are described in more detail in Section 15.11) and is used in antistatic devices in textile mills the a particles reduce static by counteracting the negative charges that tend to build up on the fast-moving fabric. 

In 1896, the French scientist Fienri Becquerel happened to store a sample of uranium oxide in a drawer that contained some photographic plates (Fig. 17.2). He was astonished to find that the uranium compound darkened the plates even though they were covered with an opaque material. Becquerel realized that the uranium compound must give off some kind of radiation. Marie Sklodowska Curie (Fig. 17.3), a young Polish doctoral student, showed that the radiation, which she called radioactivity, was emitted by uranium regardless of the compound in which it was found. She concluded that the source must be the uranium atoms themselves. Together with her husband, Pierre, she went on to show that thorium, radium, and polonium are also radioactive. 

Polonium, completing the elements of Group 16, is radioactive and one of the rarest naturally occurring elements (about 3 x 10 " % of the Earth s crust). The main natural source of polonium is uranium ores, which contain about lO g of Po per ton. The isotope 210-Po, occurring in uranium (and also thorium) minerals as an intermediate in the radioactive decay series, was discovered by M. S. Curie in 1898. 

It has been reported for many years that condensation nuclei can be produced by ionizing radiation. Recent studies have improved the measurement of the activity size distribution of these ultrafine particles produced by radon and its daughters (Reineking, et al., 1985 Knutson, et al., 1985). It seems that the Po-218 ion is formed by the radon decay, is neutralized within a few tens of milliseconds, and then attached to an ultrafine particle formed by the radiolysis generated by the polonium ion recoil. Although there will be radiolysis along the alpha track, those reactions will be very far away (several centimeters) from the polonium nucleus when it reaches thermal velocity. The recoil path radiolysis therefore seems to be the more likely source of the ultrafine particles near enough to the polonium atom to rapidly incorporate it. 

Total annual intake, in Bq/kg BW, from all sources by a 60-kg person exceeds 66 of lead-210, 166 of polonium-210, 333 of radium-226, 670 of thorium-230, 830 of thorium-228, or 1330 of uranium-238. 

Marie Sklodowska Curie (1867—1934) and Pierre Curie (1859—1906) are credited with discovering polonium as they sought the source of radiation in pitchblende after they removed the uranium from its ore. Their discovery in 1898 led to the modern concepts of the nucleus of the atom, its structure, and how it reacts. 

There are not many uses for polonium. Probably the most important is as a source of alpha particles (nuclei of helium atoms) and high-energy neutrons for research and radiation studies. It is also used to calibrate radiation-detection devices. 

Polonium is used to eliminate static electricity in industrial processes, such as rolhng out paper, wire, or sheet metal in mills. Polonium is also sometimes used in brushes to remove dust from photographic film and in the manufacturing of spark plugs that make ignition systems in automobiles more efficient, particularly in extremely cold temperatures. It can also be used as a portable, low-level power source and, since polonium is fissionable, used in nuclear weapons and nuclear electric power plants. 

Even though polonium is a rare element, it is a very dangerous radiation source and should be avoided. 

Radon s source is a step in the transmutation of several elements uranium —> thorium — radium —> radon —> polonium —> lead. (There are a number of intermediate decay products and steps involved in this process.) Radon-222 forms and collects just a few inches below the surface of the ground and is often found in trapped pockets of air. It escapes through porous soils and crevices. 

Polonium can be produced from other sources, too, that offer much higher yield than pitchblende. Two such processes are as follows ... 

Total intake from all sources Canada Lead-210 Polonium-210... 

The rarity of polonium is evident from a calculation (1) which shows that the outermost mile of the earth s crust contains only 4000 tons of the element, whereas radium, usually classed as rare, is present to the extent of 1.8 X 107 tons. The abundance of polonium in uranium ores is only about 100 Mg per ton and hence separation of the element from such mineral sources cannot seriously be considered. However, radium, at equilibrium with its daughters, contains 0.02 wt % of polonium and, until recently, most of the element was obtained either from radium itself or, more usually, from expended radon ampoules which, after the radon decay is complete, contain radium-D and its daughters. Fortunately, however, the parent of polonium in these sources, bismuth-210, can be synthesized by neutron bombardment of natural bismuth [Bi209 (n,y) Bi210] and with the advent of the nuclear reactor it has become practicable to prepare milligram amounts of polonium. Almost all of the chemistry of the element recorded in the recent literature has been the result of studies carried out with polonium-210 prepared in this way. 

In the last decade, most of the contributions to the chemistry of polonium have, rather naturally, been made by workers employed in the Atomic Energy Establishments of the United Kingdom and the United States, where milligram amounts of the element have been extracted from irradiated bismuth. Before this, all the experimental work on the element had been on the trace scale, in which quantities from 10 10 to 10 6 g were used, apart from one large source, of about 100 Mg of polonium mixed with... 

Self-heating, due to the stoppage of the alpha particles within the solid, is a well known phenomenon and calculation shows that the energy release from one gram of polonium metal would be about 140 watts. This high energy output affords a useful and absolute method for the rapid determination of polonium in large sources by calorimetry. 

There have been many reports of the wandering of polonium from open sources, behavior at one time attributed to an aggregate recoil mechanism (84), but more recent observations with curie quantities indicate that contamination only spreads when volatile compounds, for instance polonium tetrachloride, are involved. 

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