Photoexcitation ofOsm189andIrm193. I. Excitation ofOsm189by low-energy x rays

Abstract
Production of 5.84 h Osm189 by 200 through 300 kV bremsstrahlung has been measured and attributed to population of four nuclear states between 69.54 and 275.91 keV. From the measurements and known level parameters, contributions to isomer production from individual levels have been separated, and the half-life of the 216.66 keV level has been determined as 77±10 ps. Besides nuclear resonance absorption (NRA), the first level has long been assumed to be also excited by another process called nuclear excitation by electron transition (NEET), via virtual photon exchange due to recombination of vacancies produced in the K shell by incident x rays. However, contribution from competing NRA cannot be separated, and the claimed dominance or even the existence of the NEET process has remained unconfirmed.