Disintegration of Selenium-73

Abstract

The radiations from the 7.1-hour selenium-73 activity have been investigated using magnetic lens, scintillation pulse-height, and coincidence counting techniques. Two gamma rays of 65.8- and 359-kev energy and of nearly equal intensity are observed to be in prompt coincidence with each other and in delayed coincidence with annihilation radiation resulting from the positron decay of the selenium-73 parent. Energy and intensity measurements indicate that a main group ($E_{max}=1.29\mathrm{}$ Mev, $logft=5.3\mathrm{}$) excites the gamma-ray cascade, while a weaker group ($E_{max}=1.65\mathrm{}$ Mev, $log\mathrm{ft}\le 8.0$) excites the 65.8-kev transition only. These data coupled with internal conversion information lead to a level scheme in ${\mathrm{As}}^{73}$ as follows: ground level, $p_{\frac{3}{2}}$; 65.8-kev level, $f_{\frac{5}{2}}$; and 425-kev level, $g_{\frac{9}{2}}$, ${\tau }_{\frac{1}{2}}=6\mathrm{}$ μsec. The 7.1-hour level in ${\mathrm{Se}}^{73}$ is in a $g_{\frac{9}{2}}$ state.