Английская Википедия:Internal conversion coefficient
Шаблон:Short description In nuclear physics, the internal conversion coefficient describes the rate of internal conversion.
The internal conversion coefficient may be empirically determined by the following formula: <math display="block">\alpha = \frac{\text{number of de-excitations via electron emission}}{\text{number of de-excitations via gamma-ray emission}}</math>
There is no valid formulation for an equivalent concept for E0 (electric monopole) nuclear transitions.
There are theoretical calculations that can be used to derive internal conversion coefficients. Their accuracy is not generally under dispute, but since the quantum mechanical models they depend on only take into account electromagnetic interactions between the nucleus and electrons, there may be unforeseen effects.
Internal conversion coefficients can be looked up from tables, but this is time-consuming. Computer programs have been developed (see the BrIcc Program) which present internal conversion coefficients quickly and easily.
Theoretical calculations of interest are the RöselШаблон:Ref, Hager-SeltzerШаблон:Ref, and the BandШаблон:Ref, superseded by the Band-RamanШаблон:Ref calculation called BrIcc.
The Hager-Seltzer calculations omit the M and higher-energy shells on the grounds (usually valid) that those orbitals have little electron density at the nucleus and can be neglected. To first approximation this assumption is valid, upon comparing several internal conversion coefficients for different isotopes for transitions of about 100 keV.
The Band and Band-Raman calculations assume that the M shell may contribute to internal conversion to a non-negligible extent, and incorporates a general term (called "N+") which takes into account the small effect of any higher shells there may be, while the Rösel calculation works like the Band, but does not assume that all shells contribute and so generally terminates at the N shell.
Additionally, the Band-Raman calculation can now consider ("frozen orbitals") or neglect ("no hole") the effect of the electron vacancy; the frozen-orbitals approximation is considered generally superior.Шаблон:Ref
References
- Шаблон:Note F. Rösel, H.M. Fries, K. Alder, H.C. Pauli: At. Data Nucl. Data Tables 21 (1978) 91.
- Шаблон:Note R.S. Hager and E.C. Seltzer, Nucl. Data Tables A4 (1968) 1.
- Шаблон:Note I.M. Band, M.B. Trzhaskovskaya: Tables of the gamma–ray internal conversion coefficients for the K, L, M shells, 10<Z<104 (Leningrad: Nuclear Physics Institute, 1978).
- Шаблон:Note T. Kibédi, T.W. Burrows, M.B. Trzhaskovskaya, P.M. Davidson, C.W. Nestor, Jr. Evaluation of theoretical conversion coefficients using BrIcc, Nucl. Instr. and Meth. A 589 (2008) 202-229.
- Шаблон:Note http://www-nds.iaea.org/nsdd/presentations%202011/Wednesday/BrIcc_NSDD2011.pdf or see http://bricc.anu.edu.au/bricc-datatables.php
External links
- Файл:Queryensdf.jpg Nuclear Structure and Decay Data - IAEA with query on Conversion Coefficients
