Radioactive Lead Isotopes

Krishnaswami S, Graustein WC, Turekian KK, Dowd F (1982) Radium, thorium, and radioactive lead isotopes in groundwaters application to the in-situ determination of adsorption-desorption rate constants and retardation factors. Water Resour Res 6 1663-1675 Krishnaswami S, Bhushan R, Baskaran M (1991) Radium isotopes and Rn in shallow brines, Kharaghoda (India). Chem Geol (Isot Geosci) 87 125-136 Kronfeld J, Vogel JC, Talma AS (1994) A new explanation for extreme " U/ U disequilibria in a dolomitic aquifer. Earth Planet Sci Lett 123 81-93... 

The reaction of Eq. (151) indicates that the equilibrium in the system PbR4 vs Pb is shifted completely towards the side of the neso molecule, PbR4, and the most-branched building unit, tetrafunctional elemental lead. The existence of equilibria of the type of Eq. (151) is supported by the finding that hexaphenyldilead which has been tagged with radium D (a radioactive lead isotope) exchanges rapidly with tetraphenyllead (239). 

The adsorption of the dye wool violet 5BN, ha ving the formula C41H45X8O (SOaNa), on the surface of an aged precipitate of lead chromate was studied, by colorimetric analj. sis of a solution of the dye before and after equilibration with precipitate, by Kolthoff and Eggertsen (J. Amer. Chem. Soc. 1940, 62, 2125). The adsorption reached a limiting value equivalent to 4.8 mg solid dye/g PbCrO pro ided that the solution also contained sufiftcient lead nitrate. Additional experiments using the radioactive lead isotope ThB as an indicator showed that equimolecular amounts of dye and lead ions were removed from solution. 

Such studies include the decomposition of hexaphenyldilead (a) in various solvents in the presence of metal salts (337) (b) in refluxing acetic acid (308) and (c) tagged with radium D, a radioactive lead isotope, in benzene solvent in the presence of tetraphenyllead (338). 

The analytical application of radionuclides, along with other applications in radioanalysis, results directly from Hevesy and Paneth s invention of radio-tracer and radio-indication techniques in 1912. They pointed out that the addition to a solution of an element of its radioactive isotope makes possible the identification and determination of the element. In their first application they labeled a solution of lead with radium-D, a natural radioactive lead isotope and determined the solubility of sparingly soluble lead salts. 

Bie most common supply of carrier-free lead radioisotopes has been natural radium or thorium samples, Due to the presence of appreciable amounts of stable lead In pitch-blend which Is the principle source of radium or In thorium ores It Is necessary to obtain the carrier-free material from a sample which has previously been purified from lead. A convenient separation Is that of diffusion of the noble gas member of the radium or thorium decay chain from the parent material and its subsequent decay to radioactive lead Isotopes. Very early In the studies of radioactivity It was found that very high specific RaD(Pb ) sources could be obtained by... 

Lead isotope data will be discussed in three subsections of the monograph II, U-Th-Pb dating III, Common lead and IV, Radioactive lead isotopes. 

These chemical effects become important in medicine because living systems operate mostly through the reactions of enzymes, which catalyze all sorts of metabolic reactions but are very sensitive to small changes in their environment. Such sensitivity can lead to preferential absorption of some deleterious isotopes in place of the more normal, beneficial ones. One example in metabolic systems can be found in the incorporation of a radioactive strontium isotope in place of calcium. 

Thus, the ratios of lead isotopes 204,206,207 and 208 can vary markedly depending on the source of the lead. One use of these ratios lies in determination of the ages of rocks from the abundances of the various isotopes and the half-lives of their precursor radioactive isotopes. 

Ratios of lead isotopes depend on the source of the lead. They vary because lead is an end product of radioactive decay from elements of greater atomic number. 

We have at last reached lead—but 2HPb is itself radioactive This isotope decays in a succession of /3-decays ... 

Many scientists thought that Earth must have formed as long as 3.3 billion years ago, but their evidence was confusing and inconsistent. They knew that some of the lead on Earth was primordial, i.e., it dated from the time the planet formed. But they also understood that some lead had formed later from the radioactive decay of uranium and thorium. Different isotopes of uranium decay at different rates into two distinctive forms or isotopes of lead lead-206 and lead-207. In addition, radioactive thorium decays into lead-208. Thus, far from being static, the isotopic composition of lead on Earth was dynamic and constantly changing, and the various proportions of lead isotopes over hundreds of millions of years in different regions of the planet were keys to dating Earth s past. A comparison of the ratio of various lead isotopes in Earth s crust today with the ratio of lead isotopes in meteorites formed at the same time as the solar system would establish Earth s age. Early twentieth century physicists had worked out the equation for the planet s age, but they could not solve it because they did not know the isotopic composition of Earth s primordial lead. Once that number was measured, it could be inserted into the equation and blip, as Patterson put it, out would come the age of the Earth. ... 

The best sealed-in minerals are zircons, zirconium silicate minerals which are formed when melted lava on the flanks of volcanoes solidifies. When the zircons crystallize out, they incorporate radioactive uranium (in particular 238U), which decays in several steps, leading Anally to the lead isotope 208Pb. The rate of decay is very low, as the half-life of uranium-238 is 4.5 x 109 years. Thus, the U-Pb-zircon method for age determination of Precambrian rock is very important. The fossils studied by Schopf were sandwiched between two lava layers (Schopf, 1999). The volcanic layers were dated to 3.458 0.0019 x 109 years and 3.471 0.005 x 109 years the age of the fossil layer (Apex chert) was thus determined to be about 3.465xlO9 years. 

Radioactivity measurement The radioactivities of lead isotopes and their decay products were measured with TRICARB 3380 liquid scintillation counter (Packard Inc.). The radioisotopes concerned, and their decay charateristies are shown in Figure 2. In the case of the direct method, the absolute radioactivity can be obtained by the integral... 

Radioactive decay of the two main isotopes of uranium produces significant contents of the lead isotopes ° Pb and... 

Oversby, V. M. Ringwood, A. E. 1981. Lead isotopic studies of zirconolite and perovskite and their implications for long range synroc stability. Radioactive Waste Management, 1, 289-307. 

HEVESY, GEORG de (1885-1966). A Hungarian chemist who won the Nobel prize in chemistry in 1943, for his work on (he use of isotopes as tracers in the study of chemical processes. He discovered the element hafnium in 192.7. One of his interesting projects involved the calculation of ihc percentages of chemical elements in the universe. He also was involved in research using radioactive lead and phosphorus traces. His work included the separation of isotopes by physical means. His Ph D was granted ai Freiburg in 1908. 

Measurements of activity in blood of seven subjects were continued for 14 d after inhalation and showed that lead was lost from blood with a biological half-life of 18.0 (s.e.) 0.9 d. Because of radioactive decay, it was not possible to continue measurements for a longer period. Rabinowitz et al. (1976) gave oral doses of the stable lead isotope 204Pb to four subjects daily for several months, and used mass spectrometry to measure 204Pb in blood. The decline in 204Pb in blood was found to be exponential over periods of about 100 d from the end of the period of... 

The radioactive decay of 238U leads, after 14 steps, to the stable lead isotope, 20 Pb. The first of these steps is the a -decay of 238U (4.5 x 109 years half-fife), which is more than 104 times as slow (in terms of half-life) as any of the subsequent steps. As a result, the time required for the first step accounts for essentially all the time required... 

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