Lifetimes of the Low-Energy M1 Transitions in La-137 and Kr-83
Using conventional time to pulse-height techniques, the lifetimes of the low-lying levels in La"' and Kr have been measured, despite the low y-ray energies (10 and 9. 3 keV) and the large internal conversion coefBcients (130 and 11). The results of 89~4 and 147&4 nsec, respectively, correspond to retardation factors of 370 and 45 over the single-particle model predictions for those M1 transitions.
ACKNOWLEDGMENTS The help of Marcel Sidi with some of our electronic problems, and our many instructive conversations with Professor Berol Robinson, are gratefully acknowledged. One of us (S. L. Ruby) wishes to thank the Israel Atomic Energy Commission and Westinghouse Electric Corporation for the support which made it possible to undertake this work.