K-electron capture probabilities in the decays of Gd151 and Dy159

TheK-electron capture probability,P _K, in the allowed and non-unique first-forbidden transitions is measured by observing coincidences betweenK x rays and γ rays. The following results are obtained. In Gd¹⁵¹ decayP _K to the 349.8 keV level is 0.713 ± 0.015 andP _K to the 307.4 keV level is 0.813 ± 0.020. It is also deduced that the decay energyQ _EC is 491 _?9 ⁺¹⁴ keV and the spin of the 307.4 keV level is 7/2. In Dy¹⁵⁹ decayP _K to the 58.0 keV level is found to be 0.803 ± 0.032.