Investigation of internal bremsstrahlung radiation accompanying forbidden beta-decay of Er-169 and Tm-170

The internal bremsstrahlung (IB) spectrum accompanying the beta-decay of the first forbidden beta-transitions of Er-169 and Tm-170 is studied. The IB was measured using a scintillation gamma-spectrometer. It was analyzed by the variable width peeling-off-method, and then corrected by applying the proper corrections. The analyzed and corrected IB spectrum was compared with those calculated according to the original theories of Knipp and Uhlenbeck (1936) as well as of Bloch (1936) (KUB), the coulomb corrected theory of Nilsson (1956), Lewis and Ford (1957), and detour transitions of Ford and Martin (1969). Also, a new trial was carried out by applying the shape correction factor C-1 of the first forbidden beta-transition suggested by Konopinski and Uhlenbeck (1935, 1941) on the Fermi beta-decay theory to the calculated IB based on Nilsson's theory. It is called modified KUB (M.KUB). The experimental results are in a good agreement with the theoretical calculations of forbidden beta-transition of Ford and Martin (1969), and M.KUB. It is observed that the Coloumb contribution into IB spectrum is larger for lower beta-endpoint energies in case of the sources of same Coulomb charge (Z) and different beta-endpoint energies. (C) 2011 Elsevier Ltd. All rights reserved.