Failure of the allowed assumption in the element of/β+ decays of /sup 145g/Gd and /sup 143g/Sm: experimental evidence for interference effects in nuclear β decay

Anomalous ε/β⁺ decay branching ratios for "hindered allowed" transitions (measured by γ±-γ and x-γ coincidence techniques) have been found in ¹⁴⁵gGd→¹⁴⁵Eu(808.5-keV state) and ¹⁴³gSm→¹⁴³Pm(1173.2-keV state). These ratios exceed theoretical predictions by factors of 24 and 5, respectively. Thirteen additional ratios from these nuclei and ¹⁴³Eu 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.