Probability of nuclear excitation by electron transition in Os atoms

An experiment on nuclear excitation by electronic transition (NEET) induced by deexcitations of the excited atomic states was performed on ¹⁸⁹Os. Osmium targets were bombarded with both a white beam and with a monochromatic 115 keV x ray beam to produce K vacancies in Os atoms. Online K x-ray spectra were measured with a Ge detector and the L x rays emitted from the 30.814 keV isomer state in the ¹⁸⁹Os nucleus were measured offline. The NEET probability obtained from the monochromatic beam experiment was deduced to be less than 4.1×10^-10 per created K hole. This value is much lower than the values measured so far. The white beam experiment shows that these high probabilities of the NEET process in ¹⁸⁹Os, which were obtained by irradiation with white x-ray and bremsstrahlung x-ray beams, results mainly in a contribution from direct nuclear photoabsorption into the 69.537 keV state in ¹⁸⁹Os.