Detour effects on inner bremsstrahlung from the forbidden beta decays of 204Tl and 185W

The continuous spectra of internal bremsstrahlung from the beta decays of 204Tl and 185W are measured by using a multichannel NaI(Tl) scintillation spectrometer together with a standard geometrical arrangement. The total yields of intensity and of energy from each of the isotopes in the investigated energy regions are also determined and compared with the corresponding detour and direct theoretical values of Ford and Martin. For 204Tl in the photon energy region from 150 to 400 keV, the present results are coinciding with the detour theory, however, above 400 keV they are tending to correspond closely to the direct theory upto 625 keV whereas in the very low energy region below 150 keV, the experimental results are exceeding even the detour theory, the excess being 21 percent at 100 keV. For 185W, a fairly good agreement is obtained between the experiment and direct theory in the middle photon energies, while at low as well as at high photon energies even the detour theory is found to be inadequate to explain the experimental excess. (author)