235U decay series

At present, there are no widely distributed certified reference materials containing all of the radionuclides in the uranium and thorium decay series. Such reference materials are needed to calibrate instruments that make radionuclide measurements and to compare analytical results from different laboratories. The most critical need is for reference materials in the 235U decay series 231Pa, 227Ac, and 223Ra. 

Appendix 3. 235U Decay Series (major members)... 

Soft, silver white metal that is isolated in the tiniest of amounts. All isotopes are radioactive, the longest-lived has a half-life of 22 years. The element is an intermediate in the decay series of 235U. Strong alpha emitter that is used in radioactivation analysis and forms an effective neutron source with beryllium. 

Radioactive, silvery metal of which only about 125 g exists worldwide, isolated from reactor material. Protactinium occurs in the decay series of 238U (K. Fajans) as 234Pa. It also occurs in that of 235U this isotope, 231Pa, was discovered by L. Meitner and 0. Hahn. The element is only of scientific interest. 

Portion of the chart of the nuclides illustrating the decay of 235U to 207Pb. This decay series is often called the actinium series. 

The naturally occurring heavy element decay chains (see below) where 238U - 206Pb, 235U - 207Pb, and 232Th - 208Pb and the extinct heavy element decay series Np —> Bi are examples of secular equilibrium because of the... 

The terrestrial occurrence of Ac, Pa, U, and Th is due to the half-lives of the isotopes 235U, 238U and 232Th which are sufficiently long to have enabled the species to persist since genesis. They are the sources of actinium and protactinium formed in the decay series and found in uranium and thorium ores. The half-lives of the most stable isotopes of the trans-uranium elements are such that any primordial amounts of these elements appear to have disappeared long ago. However, neptunium and plutonium have been isolated in traces from uranium13 minerals in which they are formed continuously by neutron reactions such as... 

The dominant cause of the extensive isotopic variations seen in natural samples is production of noble gas nuclides by nuclear processes. The parents of simple decay schemes producing noble gases are listed in Table 3. " He is copiously produced by the 238u 235u Th decay series, each of which involves decay of various intermediate... 

There are also similar equations for both uranium-235 and thorium-232. Results embody three independent ages referring to the three decay series involved and ideally should agree. However, they will only do so if the mineral samples analyzed stayed closed throughout their geological history and also if the isotopic compositions of uranium and thorium were not modified in any way, for instance by fractionation. It is assumed that the values used for the initial lead isotopes are accurate and that no analytical or systematic errors occurred. The ratio [235u/238u] 1/137 gg for uranium of normal composition found in terrestrial minerals, lunar... 

The decay of 235U is also primarily by -decay through the actinium series (Fig. 8.15). 

The yield of each member of the isobaric series integrates, by virtue of the intervening (3 decay, the yields of its precursors. Such yields are referred to as cumulative yields. For example, the cumulative yield of the mass 140 chain in the thermal neutron-induced fission of 235U is 6.25%. 

Finally, some daughter isotopes of geochrono-logic interest result from multiparent decay. For example, virtually all " He is produced as particles released from the series decay of 235U, and Taking into consideration... 

Uranium is a radioactive element that is ubiquitous in the environment, with typical crustal and seawater concentrations of 2.7 mg kg and 3.0 pgl, respectively. Uranium-238 and U are primordial isotopes and their decay leads to the formation of series of daughter radioisotopes, amongst which is " U (Figure 1). The natural isotopic ratio of 238u 235u 234u 99.2745 0.7200 0.0055, and... 

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