Nuclide pairs

This paper is directed at illustrating the feasibility of exploiting differences in the electrochemistry of parent/daughter nuclide pairs to produce useful generator systems. The decay of a parent nuclide to its daughter involves a move from one row of the periodic table to an adjacent row. Frequently, there are drastic differences in the electrochemical nature of adjacent rows of the periodic table. Examples of such differences are shown in Table II. In each of the listed cases, the elements may be separated from one another by careful control of a potential applied to a suitable electrode. 

Table I. Examples of Parent/Daughter Nuclide Pairs For Which Suitable Generators Have Not Been Developed ...

MIRROR NUCLIDES. Pairs uf nudities, having their numhers of protons and neutrons so related that each member of the pair would be transformed into the other hv exchanging all neutrons for protons and vice versa. 

This is interpreted to indicate that 36Ar is metastable in free space Z/N < r) where it decays to 36S. However, when incorporated into a new condensing galaxy Z/N > r), enhanced gravity stabilizes the metastable nuclide, resulting in the occurrence of nuclide pairs with the same mass number and hence, elements with more than one isotope. Naturally occurring a-emitters are still in a metastable state. The same happens in about half of all cases - in four instances three stable nuclides with the same mass number are formed. The result is the formation of 81 stable nuclides from 50 starting products, in each of the even A series. 

Measurement of terrestrial mother/daughter nuclide pairs... 

Terrestrial mother/daughter nuclide pairs suitable for dating are listed in Table 16.2. Dating by means of these nuclide pairs requires evaluation of eq. (16.1). In doing this, it has to be taken into account that, in general, at time t = 0 stable nuclides identical with the radiogenic nuclides are already present. This leads to the equation... 

Table 16.2. Terrestrial nuclide pairs applicable for dating.

Nuclide pair Decay mode of the mother nuclide Half-life of the mother nuclide [y] Range of dating [y] Application... 

Figure 5 Histograms of activity ratios for key U-series nuclide pairs in compiled MORE data set (a) U/ U) by mass spectrometry, using reported In the absence of citied for all studies we did not try correcting to...

Production rate ratios Pf Be)/Pf Ne) and Pf Al)/Pf Ne). Because of the ambiguity of the parameter Ne/ Ne, other methods for deducing shielding-corrected production rates are often useful. These methods operate with a radioactive and a stable nuclide pair that have production rate ratios that can be assumed to depend only weakly on the irradiation conditions. We already mentioned the systems °Be- Ne, Al- Ne, and Mn- Ne, which can be used not only to deduce average production rates as shown above, but in principle also to derive a shielding-corrected Ne production rate for an individual sample. 

Wigner nuclides Pairs of isobars with odd nucleon numbers in which the atomic number and the neutron number differ by one. and He are examples. 

Analyses of this type are correct only if all of the product nuclide comes from radioactive decay. This is not known with certainty, but when age estimates using different pairs of nuclides give the same age and samples from different locations also agree, the age estimate is likely to be accurate. Note also that 3.8 X 10 years agrees with the qualitative limits derived from naturally occurring radioactive nuclides. 

Figure 1. (a) Schematic representation of the evolution by radioactive decay of the daughter-parent (N2/N1) activity ratio as a function of time t after an initial fractionation at time 0. The initial (N2/Ni)o activity ratio is arbitrarily set at 2. Time t is reported as t/T2, where T2 is the half-life of the daughter nuclide. Radioactive equilibrium is nearly reached after about 5 T2. (b) Evolution of (N2/N1) activity ratios for various parent-daughter pairs as a function of time since fractionation (after Williams 1987). Note that the different shape of the curves in (a) and (b) is a consequence of the logarithmic scale on the x axis in (b). 

Extremely metal-poor stars have a well defined nuclide composition for elements from C to Zn, except for C, N and Na, displaying some intrinsic scatter. This composition is in fairly well agreement with theoretical yields of primordial SNe of masses in the range 15 to 35 M , but not with those of Pair-Instability SNe. 

Another difference between nucleons and electrons is that nucleons pair whenever possible. Thus, even if a particular energy level can hold more than two particles, two particles will pair when they are present. Thus, for two particles in degenerate levels, we show two particles as II rather than II. As a result of this preference for pairing, nuclei with even numbers of protons and neutrons have all paired particles. This results in nuclei that are more stable than those which have unpaired particles. The least stable nuclei are those in which both the number of neutrons and the number of protons is odd. This difference in stability manifests itself in the number of stable nuclei of each type. Table 1.3 shows the numbers of stable nuclei that occur. The data show that there does not seem to be any appreciable difference in stability when the number of protons or neutrons is even while the other is odd (the even-odd and odd-even cases). The number of nuclides that have odd Z and odd N (so-called odd-odd nuclides) is very small, which indicates that there is an inherent instability in such an arrangement. The most common stable nucleus which is of the odd-odd type is 147N. 

The pairs of elements that are out of order based on their atomic masses are presented here, together with their atomic numbers. The periodic table lists elements in order of increasing atomic number, not increasing atomic mass. For one of these pairs there is a further explanation. Most of the Ar in the atmosphere is thought to result from the radioactive decay of 40 K, a nuclide of that once was more plentiful than it is now. 

Numerous X-ray investigations have unravelled the solid state structure of contact and solvent-separated ion pairs. It was therefore considered to be of interest to evaluate also the potential of solid state NMR as a tool for the investigation of this structural problem. In addition to the study of chemical shifts discussed above (Section II.B), the quadrupole coupling constant of the nuclide Li, x( Li), was expected to be an ideal sensor for the bonding situation around the lithium cation because, due to its dependence on the electric field gradient, the quadrupolar interaction for this spin-3/2 nucleus is strongly influenced by local symmetry, as exemplified in Section II.C.3. This is also shown with some model calculations in Section ILF. 

Ion exchange and solvent extraction techniques have been used extensively as the basis for radiochemical generators exploiting the differences in absorption behavior between the parent nuclide and its useful daughter nuclide. Many parent/daughter pairs of nuclides have sufficiently different polarographic half wave potentials so that their electrochemical behavior may be exploited for rapid separation of the daughter from the parent with minimal contamination of the product with the parent isotope. ... 

A radionuclide generator can be described as a parent-daughter pair from which the daughter nuclide is separated from the parent in as pure a nuclear form as possible throughout the operating life of the system. A variety of publications (1-3) have emphasized the general principles of the medical use and qualitative aspects of radionuclide generators. The most frequent example discussed is the Mo-99/Tc-99m system. 

Nuclide Annulus Well Well Pair Pair Pair... 

If the sample is unfractionated, the value of fn for all nuclides will be the same, but in the fractionated case very different values of fn for some of the nuclides will be observed. Any pair of nuclides, i and j, may be compared by formation of the ratio ... 

In discussing the fission-product composition of fallout samples it is advantageous to choose some fission product as a reference nuclide, j, and express the composition of the other fission products i by a set of fij ratios. For local fallout from land-surface bursts the choice of 95Zr as reference nuclide has proved convenient. A ratio of particular interest is 7 89,95 since 89Sr and 95Zr generally fractionate from each other about as severely as any pair of nuclides. Thus, r89,95 indicates approximately the maximum extent of fractionation that will be observed in the sample. 

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