Actinide isotopic abundances

The existence of a proper y-ray transition is an outcome of nuclear structure. Therefore, a Mdssbauer transition is coupled to a certain isotope of the atom of interest. A low isotopic abundance of the resonant isotope may be a serious restriction. Next, if the excited state is rather short lived then F becomes wide and the resolution for hyperfine spectroscopy (see section 2.3) becomes too limited. The same effect can be caused by unfortunate values of nuclear moments of the two states involved in the Mdssbauer transition. Finally, difficulties to produce the source activity may hinder a wider application of measurements with that particular isotope. Difficulties in source preparation and poor resolution are, for example, present in and have prevented Mdssbauer spectroscopic studies of compounds of this most interesting actinide. 

It was stated in the preceding section that 2 is a suitable choice of effective absorber thickness. Table 4 presents the needed area density of the lanthanide (in natural isotopic abundance) or the actinide for different measuring temperatures and various Debye temperatures. For intermetallic compounds 0 200 K is a good guess. A typical Mossbauer absorber covers an area of 2-4 cm. For most cases about 0.5 g of material suffices. As said before, powder samples are fine, single crystals are not necessary. 

Properties of actinide isotopes useful in neutron studies, c is the abundance or for a radioactive element the half-life (in years) in parenthesis, is the coherent scattering length (in fm, 10 cm). a, cr, ff p, (Tfission (all in b = 10 cm ) are the coherent, incoherent, capture, and fission cross sections, respectively. All refer to an energy of 25.3 meV, neutron velocity 2200m/s, wavelength = 1.8 A. (Adapted from Sears... 

These drawbacks of the Rosholt isochron largely disappear when used for igneous systems, where Th, being the most-abundant actinide, is measured with approximately equal or better precision than the other U-Th isotopes, thus minimizing error correlations. In fact, for data where all analyses have relatively high Osmond diagrams can... 

Regelous et al have reported ou the use of the isotope dilutiou techuique (using a Pa spike with a half-life of 26.97 days) for the quantitative measurement of 20 fg of protactinium in silicate rocks after chemical separation of the actinide from the rock matrix by MC-ICP-MS (Neptune, Thermo Fisher Scientific, Bremen - equipped with uiue Faraday detectors, oue secondary electron multiplier and a retarding potential quadrupole for high abundance sensitivity measurements). 

Nuclear reaction(s) producing noble gas isotope(s) from stable or long-lived isotope during an irradiation in a nuclear reactor, or parent isotopes with half-lives less than 10 years, typical or suspected abundance at the time of formation of the solar system. For longer-lived parent isotopes, current abundance (%) of element. For actinides, " He yields are the number of atoms produced per decay chain, fission Xe yields are branching ratio for Xe. Yields for other isotopes are given in Table 2. 

One difficulty is that there is no stable isotope of plutonium with which to compare its abundance. To really quantify its abundance, it is necessary to consider the amount of " " Pu relative to an isotope of a similar element. The definition of similar depends on the problem to be addressed. In studies of nucleosynthesis, the similar element used is usually uranium, another actinide, which is produced in the same stellar environments. In studies of the history of specific meteorite parent bodies, the similar element is more commonly a light rare earth element (TREE) like neodymium, since the geochemical behavior of plutonium is apparently most similar to that of the LREE. We will discuss the details of the experimental technique of each approach below. 

Lead (208) constitutes about 52% of most naturally occurring lead deposits, and is therefore abundant however, an economic isotope separation method is necessary to ensure the economic viability of utilizing lead (208) as a coolant.. There is also the potential for obtaining lead (208) from specific actinide decay chains for example the thoria chain yields essentially pure lead 208, although quantities are small. 

There has not been any solid-state chemistry reported for pure bulk forms of the transeinsteinium elements, due to the small amounts of the elements that have been available and their short lives. The most abundant of these elements is Fm [nanograms of a very short-lived (20 h) Fm-255 isotope] and the above limitations have precluded studying its oxide. When reaching the end members of the actinide series, the availability of isotopes is a much greater problem e.g., only a few atoms of a short-lived isotope of Lr can be produced. 

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