Total internal conversion coefficient

Not all nuclear transitions of this kind produce a detectable y-ray for a certain portion, the energy is dissipated by internal conversion to an electron of the K-shell which is ejected as a so-called conversion electron. For some Mossbauer isotopes, the total internal conversion coefficient ax is rather high, as for the 14.4 keV transition of Fe (ax = 8.17). ax is defined as the ratio of the number of conversion electrons to the number of y-photons. 

Total internal conversion coefficient Recoil energy (in 10 eV)... 

The theory of internal conversion is explained in detail, e.g., by Rose (1965). Numerical values of internal conversion coefficients have been published by Band et al. (1976) and Rosel et al. (1978). Selected theoretical partial and total internal conversion coefficients are presented in the form of graphs for Ml, M2, M3, M4, El, E2, E3, and E4 transitions in Firestone et al. (1996). (Here E and M stand for electric and magnetic transitions, and the number following the symbol is just L.) The accuracy of the graphs is 3-5%. 

Theoretical total internal conversion coefficients for electric (E) and magnetic (M) multipole transitions in the energy range 10 keV to 1 MeV for the atomic number 10... 

Mossbauer transitions are usually highly converted and are followed by the emission of characteristic X-rays and Auger electrons. (The total internal conversion coefficient is high. For most cases de-excitation of the nucleus is via the emission of conversion electrons followed by rearrangement of the excited atomic shell by X-ray emission and Auger processes. More than one electron is produced per resonant scattering event.) The detection of electrons has proved in many cases to be the most efficient means... 

The iatensity of a conversion fine can be expressed relative to that of the associated y-ray as the internal-conversion coefficient (ICC), denoted as d. For example, is the ratio of the number of electrons emitted from the K atomic shell to the number of photons emitted. For the other atomic levels, the corresponding conversion coefficients are denoted by (X, The total conversion coefficient is a = n, where the sum iacludes all atomic... 

One can define this ratio, the internal conversion coefficient, for electrons from the K shell only for electrons from the M shell only, and so on, giving rise to aK, aM, and so on. Since the total probability of decay must equal the sum of the probabilities of decay via various paths, we have... 

Internal conversion coefficients (ICC) were obtained from relativistic self-consistent-field Dirac-Fock calculations by Band et al. (2002). They presented results for E1,...E5, M1,...M5 transitions in the energy range Ey= 1 — 2,000 keV for K, Li, L2, L3 atomic shells of elements Z = 10 — 126. The total ICCs and graphs for ICCs were also published. The Dirac-Fock values are in better agreement with experimental results than the relativistic Hartree-Fock-Slater theoretical ones. 

Fig. 25 Internal conversion coefficients for fermium calculated with BrICC [65]. The full lines show the total conversion coefficients for E2 and Ml transitions while the dashed curves show the K-conversion coefficients only...

For the spectroscopy of nuclei around Z 100 this means that E2 transitions below 200 keV as well as Ml transitions below 400 keV are dominated by internal conversion. A realistic case is calculated for fermium and shown in Fig. 25. Here the total conversion coefficients for 2 and Ml transitions are shown as a ftmction of transition energy. We also show the coefficients for K-conversion in the same graph. It is clear that a measurement of the ratio of the K-conversion coefficient to the total conversion coefficient is sensitive to the multipolarity of the transition. Special attention has to be paid to transitions in the vicinity of binding edges where the conversion coefficient can vary rapidly with energy. 

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