Beta-Gamma Emission through Virtual States

Abstract

The possibility of observing a combined beta-gamma transition through a virtual intermediate nuclear state in competition with a direct forbidden beta decay is investigated. Such a transition is coherent with ordinary inner bremsstrahlung associated with the direct transition and can therefore be observed through the distortion of the gamma-ray spectrum from the form predicted for inner bremsstrahlung alone. Favorable circumstances occur particularly when the intermediate state of the daughter nucleus is nearly degenerate with the ground state of the parent. The $K$-capture transition in ${\mathrm{Ni}}^{59}$ appears to offer the best possibility for such an observation. The direct observation of negative-helicity gamma rays with appropriate spectrum would be another way of directly establishing the alternate decay mode.