Failure of the Allowed Assumption in the $\frac{ε}{β^{+}}$ Decays of ${}^{145 g}{Gd}$ and ${}^{143 g}{Sm}$ —Experimental Evidence for Interference Effects in Nuclear $β$ Decay

Anomalous

\frac{ε}{β^{+}}

decay branching ratios for "hindered allowed" transitions (measured by

γ^{\pm} - γ

and x-

γ

coincidence techniques) have been found in

{}^{145 g}{Gd} \to {}^{145}{Eu} (808.5 - keV state)

and

{}^{143 g}{Sm} \to {}^{143}{Pm} (1173.2 - keV state)

. These ratios exceed theoretical predictions by factors of 24 and 5, respectively. Thirteen additional ratios from these nuclei and

{}^{143}{Eu}

agree with the predictions. This is the first conclusive evidence of the failure of the allowed assumption in nuclear

β

decay and of the presence of interference effects.

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Failure of the Allowed Assumption in theεβ+Decays ofGd145gandSm143g—Experimental Evidence for Interference Effects in NuclearβDecay