A Study on the Yield of (γ, α) Reactions with 20 MeV Bremsstrahlung

The yields of the (γ, α) reactions on 7 elements up to an atomic number of 49, irradiated with 20 MeV bremsstrahlung, have been obtained through gamma-ray spectrometric measurements of the resultant activities. The yield values, as measured in absolute disintegration rates at the end of irradiation per mole per roentgen, have been plotted against atomic number of the target nuclides. The yield curve shows a maximum in the region of copper and zinc, and drops rapidly with increasing atomic number. The shape of this yield curve is similar to that for the photoalpha yield as a function of atomic number. It can be seen that the yield levels off in the region of silver and indium. A mechanism such as the direct photoelectric effect is thought to be responsible for this behavior. The yield of the (γ, α) reaction of an element amounts to only a small fraction, at most a few tenths of a per cent, of the total photonuclear yield.