Polonium fraction

It will be recalled that is 100% abundant and is the heaviest stable nuclide of any element (p. 550), but it is essential to use very high purity Bi to prevent unwanted nuclear side-reactions which would contaminate the product Po in particular Sc, Ag, As, Sb and Te must be <0.1 ppm and Fe <10ppm. Polonium can be obtained directly in milligram amounts by fractional vacuum distillation from the metallic bismuth. Alternatively, it can be deposited spontaneously by electrochemical replacement onto the surface of a less electropositive metal... 

Radon daughters are deposited on the surface of mucus lining the bronchi. It is generally assumed that the daughter nuclides, i.e. polonium-218 (RaA), lead-214 (RaB) and bismuth-214 (RaC), remain in the mucus and are transported towards the head. However, one dosimetric model assumes that unattached radon daughters are rapidly absorbed into the blood (Jacobi and Eisfeld, 1980). This has the effect of reducing dose by about a factor of two. Experiments in which lead-212 was instilled as free ions onto nasal epithelium in rats have shown that only a minor fraction is absorbed rapidly into the blood (Greenhalgh et al., 1982). Most of the lead remained in the mucus but about 30% was not cleared in mucus and probably transferred to the epithelium. 

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 ]. 

The method of treatment consisted in effecting a concentration of some of the constituents of the residues and observing the radioactivity of the various portions into which the material was divided. It was observed that if barium was concentrated the radioactivity of that portion increased rapidly. From a ton of residues there may be prepared 10-20 kilograms of crude sulfate whose activity is about 60 times that of uranium. The Curies then converted the sulfates to chlorides and subjected the material to the process of fractional crystallization. After a number of crystallizations there was obtained in the most insoluble portion a fraction, of a gram of radium chloride which was a million times as active as uranium, One ton of pitchblende is said to contain 0.37 gram of radium, 0.00004 gram of polonium,1 and a small amount of aetinium. 

OF ORE TO A FEW GRAMS OF RADIOACTIVE SUBSTANCE. QHEY SUCCEEDED IN SHOWING THAT THE ORE CONTAINED TWO NEW RADIOACTIVE ELEMENTS, POLONIUM AND RADIUM. 0Y A LONG SERIES OF LABORIOUS FRACTIONAL CRYSTALLIZATIONS, THEY FINALLY ISOLATED A SMALL QUANTITY OF PURE RADIUM SALT. 

Mme Curie noticed that certain pitch-blendes show greater activity than corresponds to their uranium content, and concluded that this was due to the presence of an unknown element, much more active than uranium itself, but present in such minute quantities that it had escaped detection by the ordinary methods of analysis. Upon request the Austrian Government very generously placed a ton of pitch-blende residues from their state Dollar Mine at Joachimstal, at the disposal of Mme Curie. This, with the collaboration of her husband, she fractionated according to accepted qualitative methods of analysis, each precipitate being tested electroscopically for radioactivity and rejected when inert. In this way the radio precipitates were concentrated, and two radiosubstances eventually separated in 1898. One of these was precipitated with bismuth and was named polonium, in honour of Poland, Mme Curie s native land the other was precipitated with the barium and was christened radium, because of its great activity. ... 

Since Mosander thus fractioned the gadolinite earths in 1839, the method has been extensively employed by W. Crookes (Ghem. News, 54, 131, 155, 1886), in some fine work on the yttria and other earths. The recent separations of polonium, radium and other curiosities have attracted some attention to the process. The mathematics of the reactions follows directly from the law of mass action. Let only sufficient C be added to partially precipitate A and B and let the solution originally contain a of the salt A, b of the salt B. Let x and y denote the amounts of A and B precipitated at the end of a certain time t, then a - x and b - x will represent the amounts of A and B respectively remaining in the solution. The rates of precipitation are, therefore,... 

Although the rate of production of Po-210 by this two-step process is much lower (1000 times lower), fraction of polonium migration out of the coolant is higher (perhaps, by 100 times) because of higher coolant temperature. 

The challenge of initiator development was to design a source of sufficient neutron intensity that released those neutrons only at the precise moment they were needed to initiate the chain reaction. In the case of the uranium gun that requirement would be relatively easy to meet, since the alpha source and the beryllium could be separated with the bullet and the target core. But the implosion bomb offered no such convenient arrangement for separation and for mixing. Polonium and beryllium had to be intimately conjoined in Fat Man at the center of the plutonium core but inert as far as neutrons were concerned until the fraction of a microsecond when the imploding shock wave squeezed the plutonium to maximum density. Then the two materials needed instantaneously to mix. 

When the Curies and G. Bemont analysed pitchblende they noticed a higher radioactivity of one more fraction, apart from the bismuth fraction. After they had succeeded in extracting polonium they started to analyse the second fraction thinking that they could find yet another unknown radioactive element. 

Almost immediately after the discovery of radioactivity, Marie Sklodowska Curie and Pierre Curie began more detailed studies of the new phenomenon. Guided by their observation that some natural uranium ores, such as pitchblende, were more highly radioactive than corresponded to their uranium content (Sklodowska Curie 1898), they fractionated the ores chemically, using the intensity of radioactivity in the fractions as evidence for further radioactive substances. The result was the discovery, in June 1898, of a new radioactive element in the bismuth fraction (Curie and Curie, 1898) the Curies named it polonium in honor of Marie s homeland. A few months later, in December 1898, they were able to report the discovery of another radioactive element, this one in the barium fraction separated from pitchblende (Curie et al. 1898) they named it radium. The subsequent isolation of radium from barium was accomplished by fractional crystallization of barium chloride, with radium chloride always being enriched in the crystalline phase. It soon became possible to characterize radium spectroscopically by optical emission lines (Demar9ay 1898) and, thus, to confirm the discovery by an independent identification. By 1902, M. Curie had isolated 120 mg of pure... 

Collect the fractions. Gold, mercury and polonium (RaP) come off quantitatively In a narrow band after one column volume of eluant Is passed through the column. Carrier-free bismuth (RaE) comes off about two column volumes later. One or two column volumes later carrier-free lead (RaD) Is eluted. 

Curie measured the intensity of the radiation from the mineral pitchblende. The principal metal in pitchblende is uranium, but smaller quantities of many other metals are present as well. Curie found that the radioactivity of pitchblende was considerably greater than could be explained on the basis of its uranium content, and she concluded that there was an unknown and highly radioactive element present. She dissolved some pitchblende in acid and precipitated each metal in turn and checked with the electrometer to see if the radioactivity had come out of solution. She found that a high radioactivity was associated with the bismuth fraction, and named the new element which was clearly present polonium in honour of her native country. However, the spectrum of the precipitate contained no new lines, so it appeared that polonium must be present in extremely small quantity. 

With her husband. Professor Pierre Curie (1859-1906), she began to separate pitchblende into fractions and to determine their activity in discharging the electroscope. She isolated a fraction that was 400 times more active than uranium. This fraction consisted largely of bismuth sulfide. Since pure bismuth sulfide is not radioactive, she assumed that a new, strongly radioactive element, similar in chemical properties to bismuth, was present as a contaminant. This element, which she named polonium, was the first element discovered through its properties of radioactivity. In the same year, 1896, the Curies isolated another new radioactive element, which they named radium. 

Discovery Polonium was discovered in connection with the investigation of the ore pitchblende by the French scientists Marie and Pierre Curie in 1898. They discovered that the ore was more radioactive than its principal component, uranium, and they separated the ore into many chemical fractions in order to isolate the unknown sources of radioactivity. One fraction, isolated by use of bismuth sulfide, contained a strongly radioactive substance that the Curies showed was a new element. They named it polonium after Poland. 

From a solution containing iron and some rare earth metals, Debierne precipitated a mixture of hydroxides. It was radioactive, an activity that could not have its origin in uranium, radium or polonium. A new element could be isolated by fractional crystallization of magnesium lanthanum nitrate. The element was named actinium after the Greek word aktinos, meaning ray . Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300°C. 

Estimation of Radioactivity.— The 8-ray activity of the lead used indicates that it contains in about 2 parts so-called radium G and 1 part lead, an amount of radium D of the order of 10 parts. This is betrayed by the steady growth of a penetrating jS-ray product (RaE) which comes to practical equilibrium with its parent in about a month after they are separated. Evidently the ionization— if the a-rajre from the polonium present are cut off—caused by a weighed amount of the material imder constant conditions, is a measure of the concentration of radium D relative to its isotopes radimn G and lead. Thus the determination of the activity of the end fractions gives information as to the relation between the solubility of the nitrate of radium D and the mean solubility of the nitrates of radium G and ordinary lead, a relation of great interest because it cannot be tested by atomic weight determinations. This case should afford an especially favorable test of the theory of complete identity. 

Even though some of the daughters in natural radioactive decay schemes have very short half-lives, all are present because they are constantly forming as well as decaying. It is likely that only about one gram of radium-226 was present in several tons of uraniiun ore processed by Marie Curie in her discovery of radium in 1898. Nevertheless, she was successful in isolating it. The ore also contained only a fraction of a milligram of polonium, which she was able to detect but not isolate. 

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