Radon-226, neutron bombardment

Radon-211, in preparation of astatine, 31 49 Radon-226, neutron bombardment, 31 16 Rain... 

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. 

Bromine Exchange Between Bromine and Bromide Ion. A solution of sodium bromide, 20 grams in 200 cc. of water, was bombarded for twenty-four hours with neutrons from 100 millicuries of radon and 200 milligrams of beryllium. Two radioactive forms of bromine are produced but one is of short life and the second one... 

Aliphatic Substitution and the Walden Inversion. The rate of substitution of radioactive iodine into sec-octyl iodide in acetone was found to be the same as the rate of racemization of d-sec-octyl iodide by sodium iodide. The radioactive iodine was produced by bombardment with neutrons from 150 millicuries of radon mixed with beryllium and embedded in paraffin. 

The cyclotron was used as the source of neutrons. In the previous experiments beryllium was bombarded at the target chamber with about one microampere of 8 Mev protons. This corresponded to about 3500 curies radon beryllium equivalent. Lately it has been found that the neutron intensity at the graphite block is increased by a factor of about ten if the beryllium is bombarded internally on a probe this increase occurs even though the probe is about 30 cm farther away from the block than is the usual target. 

Mathur and Hyde studied neutron deficient xenon isotopes produced by bombardment of KI with 100-Mev protons using a similar procedure. The KI was dissolved with water in a closed system and the xenon removed from solution by pumping through the same series of traps used in the radon procedure. The NaOH scrubbing was omitted. 

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