Polonium-212, alpha activity

At trace levels, polonium can be separated effectively by solvent extraction, ion exchange, paper chromatography, and other techniques. Diisopropyl ketone, di-n-octylamine, and tri-n-butylphosphate are suitable solvents for extraction. Trace amounts of polonium in solutions or sohd mixtures containing no other emitters can be determined by measuring its alpha activity. 

Polonium-210 alpha activation of beryllium to yield neutrons that in turn are used to start up nuclear reactors... 

The levels of polonium and iodine on filter papers, exposed for a three-day period during the incident, at Harwell and also in the Netherlands show approximately the same ratio of 1131 activity to alpha activity [polonium 210isanalpha emitter], namely, 25 1. The continuous inhalation maximum permissible levels are in the... 

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. 

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. 

Reactions used for the preparation of polonium compounds are straightforward, but the experimental techniques are strictly determined by the small amount of the commonly used polonium-210 which is available and by the exceptionally high specific activity of the isotope (4.5 curics/mg, i.e., 1013 disintegrations/min/mg). Apart from the major effects of the alpha bombardment to be described, the separation of polonium-210 from its lead daughter, which grows in at a rate of 0.5%/day, constitutes a major chemical problem. It calls for rapid and efficient methods of purifying the polonium stock before each experiment the best of these is the sulfide process described in Section III. 

After separation and purification, the pure fractions of uranium and plutonium are electroplated on polished stainless discs and the activities of their radionuclides measured using alpha spectrometry. The distribution value of alpha detectors, which is between 17 and 20 kev, is very important. Two radionuclides ( Pu and " °Pu) are measured together because the difference between the energy of their alpha particles is less than 15 keV [1, 14]. Figures 15.3, 15.4, and 15.5 present typical spectra for the alpha measurement of polonium, uranium, and plutonium [ 1 ]. 

Write nuclear equations for (a) alpha emission hy polonium-210, used in radiation therapy, (b) beta emission by gold-198, used to assess kidney activity, (c) positron emission by nitrogen-13, used in making brain, heart, and liver images, and (d) electron capture by gallium-67, used to do whole body scans for tumors. 

As can be seen in Figure 1, radon itself and its polonium daughter products are alpha emitting nuclides, while the isotopes of lead and bismuth produced are beta/ gamma emitters. The short half-lives of the daughter products prior to Pb (Table 2) result in the rapid production of a mixture of airborne radioactive materials which may attain equilibrium concentrations within a relatively short time. The half-life of °Pb is 22 years and at this point in the decay chain any activity inhaled is largely removed from airways in which it is deposited before any appreciable decay occurs. 

Here one must deal in terms of theory, as far as human activity goes, since there are no non-radioactive isotopes of polonium. The only readily available isotope is that with mass 210, which is also called Radium F, and is an alpha-particle emitter. If this were ever to be put into a living organism, and if it were to seek out and hang around some particular site of action, that area would be thoroughly and completely cooked by alpha-particle emission. It would be a fun academic exercise to make 2C-P0... 

Because radon has such a short half-life and because alpha particles have a high RBE, inhaled radon is considered a probable cause of lung cancer. Even worse than the radon, however, is the decay product because polonium-218 is an alpha-emitting chemically active element that has an even shorter half-life (3.11 min) than radon-222 ... 

Thus, we may regard 18 July, 1898, as the date of just a preliminary discovery of polonium as substantiation of the discovery took quite a long time. The high intensity of radiation from polonium made difficult its study. The radiation was found to consist of only alpha rays with no beta or gamma rays. A strange finding was that the activity of polonium decreased with time and the decrease was rather noticeable neither thorium nor uranium exhibited such behaviour. This is why some scientists doubted whether polonium existed at all. The sceptics said it was just normal bismuth with traces of radioactive substances. 

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