Isotopes longer lived

In 1965, the Dubna workers found a longer-lived lawrencium isotope, 256Lr, with a half-life of 35 s. In 1968, Thiorso and associates at Berkeley used a few atoms of this isotope to study the oxidation behavior of lawrencium. Using solvent extraction techniques and working very rapidly, they extracted lawrencium ions from a buffered aqueous solution into an organic solvent — completing each extraction in about 30 s. 

In this chapter we discuss improvements documented in the literature over the past decade in these areas and others. Chemical procedures, decay-counting spectroscopy, and mass spectrometric techniques published prior to 1992 were previously discussed by Lally (1992), Ivanovich and Murray (1992), and Chen et al. (1992). Because ICPMS methods were not discussed in preceding reviews and have become more commonly used in the past decade, we also include some theoretical discussion of ICPMS techniques and their variants. We also primarily focus our discussion of analytical developments on the longer-lived isotopes of uranium, thorium, protactinium, and radium in the uranium and thorium decay series, as these have been more widely applied in geochemistry and geochronology. 

In these situations, addition of a tracer of unique isotopic composition is required, and the nature of the tracers added depends on the measurement technique. For example, short-lived and Th (with respective half-lives of 70 and 1.9 years) are commonly used as a tracer for alpha spectrometric analysis of U and Th, whereas longer-lived... 

Most of the radioactive isotopes of cerium have very short physical half-lives and do not normally represent a radiological hazard to humans. Only the three longer-lived isotopes, 141Ce, l3Ce, and H4Ce,... 

Figure 4. The decay schemes of 23SU and 235 U, showing the longer-lived isotopes used in radiometric dating of Pleistocene and Holocene deposits.

Because of some of its longer-lived isotopes, cesium has become valuable for its ability to produce a steady stream of beta particles (p) as electrons. 

Plutonium has a longer-lived isotope than Pu, and it may turn out that some of the larger superheavy elements also have isotopes with greater longevity than those indicated here. Nevertheless, the trend is clear enough. 

Cl) samples were irradiated in a reactor with thermal neutron flux of 6 X 1013 neutrons/cm2/sec for 2 secs and counted with a large volume Ge(Li) detector. 3 samples of 10 mg each were used. For longer lived isotopes (Cu, Sn, Co, Ag, Au, and Sb) samples were irradiated for 1 hr, cooled for 7 days, diss. in HN03-HF and made up to standard volume for counting. Pure metal foil standards were used for Cu, Sn, Co, Au pure NH4C1 was used for Cl and pure Sb3 for Sb. In calculated from intensity of 116mIn, 1.26 Mev 7 relative to 64Cu 1.34 Mev 7. 

The fissioning of U and Pu in a nuclear reactor produces a large number of radioactive fission products. Most of these decay to stable isotopes within a few minutes to a few years after the fuel has been discharged from the reactor and therefore pose no problem in the management of nuclear fuel wastes. There are, however, a number of longer lived radionuclides that must be considered in assessing the environmental impact of any nuclear fuel waste disposal vault in the geosphere. 

Pu/U In contrast to I, the element Pu has no stable isotope, nor any longer-lived isotope than 244Pu. Hence, the abundance of 244Pu must be indexed to an isotope of a... 

Many radionuclides can be produced in cyclotrons, thus avoiding the use of more costly nuclear reactors. Many research hospitals now have cyclotrons to provide shortlived radionuclides of carbon, nitrogen, oxygen, and fluorine. The longer-lived products are produced commercially or in government laboratories.25,26 28A list of major isotopes and their uses is shown in Table 21.9,... 

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