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

The internal bremsstrahlung (IB) spectrum accompanying the β-decay of the first forbidden β-transitions of 169Er and 170Tm is studied. The IB was measured using a scintillation γ-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 C1 of the first forbidden β-transition suggested by Konopinski and Uhlenbeck (1935, 1941) on the Fermi β-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 β-transition of Ford and Martin (1969), and M.KUB. It is observed that the Coloumb contribution into IB spectrum is larger for lower β-endpoint energies in case of the sources of same Coulomb charge (Z) and different β-endpoint energies. -- Research highlights: → Internal bremsstrahlung radiations of 169Er and 170Tm are measured. → The experimental results are compared with five theoretical calculations. → The experimental results are in a good agreement with modified KUB theory. → Modified KUB takes into account the Coulomb effect and the detour effect.