Mother nuclide

Mo/"mTc Generators The essential part of the most commonly available generator system is a simple chromatography column to which the mother radionuclide is absorbed on a suitable support material. The daughter radionuclide is a decay product of the mother nuclide. Since it is the daughter nuclide that is used to label the carrier molecules, it must be possible to separate this from the parent nuclide by a chemical separation. 

The genetic correlations of the radionuclides within the families are often characterized by the terms mother and daughter . Thus, is the mother nuclide of all members of the uranium family, Ra is the mother nuclide of Rn, and so forth. 

Even if AE > 0, the question of the probability of a radioactive decay process is still open. It can only be answered if the energy barrier is known. The energetics of radioactive decay are plotted schematically in Fig. 4.1. The energies of the mother nuclide and the products of the mononuclear reaction differ by AE. But the nuclide A has to surmount an energy barrier with the threshold energy Es. The nuclide may occupy discrete energy levels above ground level. However, only if its excitation... 

In words nuclide 1 is transformed by radioactive decay into nuclide 2, and the latter into nuclide 3. Nuclide 1 is the mother nuclide of nuclide 2, and nuclide 2 the daughter nuclide of nuclide 1. At any instant, the net production rate of nuclide 2 is given by the decay rate of nuclide 1 diminished by the decay rate of nuclide 2 ... 

Assuming that mother and daughter nuclide are separated from each other at time t = 0, the growth of the daughter nuclide in the fraction of the mother nuclide and the decay of the daughter nuclide in the separated fraction are plotted in Fig. 4.3. The logarithms of the activities are plotted in Fig. 4.4. The solid curves can be... 

Figure 4,3. Decay of the daughter nuclide and its formation from the mother nuclide in the case of secular equilibrium as a function of t/ti/2(2).

The activities of the mother nuclide and of all the nuclides emerging from it by nuclear transformation or a sequence of nuclear transformations are the same, provided that secular radioactive equilibrium is established. 

Half-life of Mother Nuclide Shorter than Half-life of Daughter Nuclide... 

In this case the mother nuclide decays faster than the daughter nuclide, and the ratio between the two changes continuously, until the mother nuclide has disappeared and only the daughter nuclide is left. The situation is plotted in Fig. 4.6. No radioactive equilibrium is attained. 

Figure 4.6. Half-life of mother nuclide shorter than that of daughter nuclide - no radioactive equilibrium (tl/2(l)Al/2(2) =0.1).

As the difference between the half-lives of mother nuclide and daughter nuclide becomes smaller and smaller, the attainment of radioactive equilibrium is more and more delayed, as can be seen from eq. (4.20) and from Fig. 4.2, provided that ti/2(l) > 1/2 (2). In this situation, the following questions are of practical interest ... 

If the time t is small compared with the half-life of the mother nuclide A t q/2(A)), it follows from eqs. (4.43) that... 

In the previous sections the radioactive equilibrium between a mother nuclide and a daughter nuclide according to eq. (4.13) has been considered. This can be extended to a longer sequence of successive transformations ... 

If the half-life of the mother nuclide is much longer than those of the succeeding radionuclides (secular equilibrium), eq. (4.48) becomes much simpler, provided that radioactive equilibrium is established. As in this case At A2, A3... Aa, all terms are small compared with the first one, giving... 

Proton activity was observed for the first time for Tm (ti/2 = 0.56s) and Lu (h/2 = 90 ms), both produced at the UNILAC accelerator of GSI (Darmstadt, Germany) in 1982. Both nuclides emit monoenergetic protons of 1.05 and 1.23 MeV, respectively, by transmutation of the ground state of the mother nuclide into the ground state of the daughter nuclide ... 

The energy AE in eq. (5.43) can be calculated by comparing the masses of the mother nuclide and the products. It is found that for mass numbers A 200, AE amounts to about 200 MeV. Comparison of the masses shows that AE is already positive for /f > 100, indicating that all nuclides above Z 46 (Pd) are unstable with respect to fission. The fact that these nuclides do not exhibit spontaneous fission is due to the high energy barrier. 

Mdssbauer spectrometry gives information about the chemical environment of the Mdssbauer nuclide in the excited state at the instant of emission of the photon. It does not necessarily reflect the normal chemical state of the daughter nuclide, because of the after-effects that follow the decay of the mother nuclide (recoil and excitation effects, including emission of Auger electrons). At very short lifetimes of the excited state, ionization and excitation effects may not have attained relaxation at the instant of emission of the y-ray photon this results in a time-dependent pattern of the Mdssbauer spectrum. 

Application of short-lived radionuclides has the advantage that the activity vanishes after relatively short periods of time. This aspect is of special importance in nuclear medicine. Short-hved radionuclides may be produced by irradiation in nuclear reactors or by accelerators, but their supply from in-adiation facilities requires matching of production and demand, and fast transport. These problems are avoided by application of radionuclide generators containing a longer-lived mother nuclide from which the short-hved daughter nuclide can be separated. 

It was named in analogy to uranium after the planet Neptune. The Np isotope with the longest half-life (O/2 2.144 10 y) is Np, the mother nuclide of the (artificial) decay series with A = An + (section 4.1). It is produced in nuclear reactors ... 

On the other hand, the concentration of stable decay products, such as He, Pb, 208pb 207p 5 40(daughter of and Sr (daughter of Rb), increases continuously with time. If one stable atom (subscript 2) is formed per radioactive decay of the mother nuclide (subscript 1), the number of stable radiogenic atoms is... 

A is the number of atoms of the mother nuclide at r = 0). For dating, N2 and N have to be determined. If several stable atoms are formed per radioactive decay of the mother nuclide, as in the case of He formed by radioactive decay of Th,... 

The main problems with application of cosmogenic radionuclides are knowledge of the production rate during the time span of interest and the possibility of interferences (e.g. by nuclear explosions). For the other methods it is important whether the systems are closed or open, i.e. whether nuclides involved in the decay processes (mother nuclides, daughter nuclides or a particles in the case of measurement of He) are lost or entering the system during the time period of interest. 

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

In practice, two approaches are used - independent determination of N2 and N or simultaneous determination of N2 and N by mass spectrometry (MS). The second approach is not applicable if the properties of the mother nuclide and the daughter nuclide are very different, e.g. in the case of dating by the " °K/" °Ar method or by measuring " He formed by radioactive decay. Both methods require additional determination of the unknown number but in special cases A can be neglected. 

Systems for which the loss of members of the decay chains can be neglected and in which the concentration of the mother nuclide can be taken as a measure of the age. For these systems eq. (16.4) can be applied in the forms... 

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