LEVELS IN $sub 75$Re$sup 188$ FROM STUDIES OF THE DECAY OF $sub 74$W$sup 188$ (69.4 DAY), $sub 75$Re$sup 188$ (18 h), AND $sub 75$Re$sup 188$m (18.5 MIN)

Sources of the 69.4-day ${\ensuremath{\beta}}^{\ensuremath{-}}$ emitter $_{74}\mathrm{W}^{188}$ were produced by successive capture of two neutrons in ${\mathrm{W}}^{186}$. A study with a double-lens spectrometer revealed the presence of a 349\ifmmode\pm\else\textpm\fi{}3-keV beta ray decaying to the ground state of $_{75}\mathrm{Re}^{188}$. A 285-keV beta-ray component to the 63.7-keV level in ${\mathrm{Re}}^{188}$ was observed in coincidence experiments. The 59-keV beta-ray branch populating the 290.3-keV level in ${\mathrm{Re}}^{188}$ was not directly observed. The source used for the study of the beta-ray spectrum of ${\mathrm{W}}^{188}$ contained an equilibrium concentration of the 18-h daughter ${\mathrm{Re}}^{188}$; hence, some of the properties of this latter beta decay were also examined. Scintillation and coincidence studies on sources of ${\mathrm{W}}^{188}$ from which the daughter activity had been removed chemically showed the presence of three gamma transitions: 63.7, 226.7, and 290.3 keV. The former two are found to be in coincidence. Internal-conversion-electron studies with photographic spectrographs showed lines from all of the above transitions. Scintillation measurements on the gamma-ray spectrum of the 18.5-min isomeric activity in ${\mathrm{Re}}^{188}$ showed the presence of three gamma transitions with energies of 63.7, 92.8, and 105.9 keV. The latter two gamma rays are both in coincidence with the 63.7-keV transition but not in coincidence with each other. In addition to internal-conversion-electron lines from these three transitions, spectrographic studies revealed one line at 11 keV which is interpreted as the $M$ line of a transition of 14\ifmmode\pm\else\textpm\fi{}1.0 keV. It is concluded that the 92.8- and 105.9-keV transitions depopulate energy levels at 156.5 and 169.6 keV. All of the transitions observed in both activites, i.e., 63.7, 92.8, 105.9, 226.7, and 290.3 keV, are assigned $M1$ character. From this fact and a consideration of transition rates and possible spin assignments, we conclude that both the 156.5- and the 169.6-keV states have spin ${I}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$ and that the isomeric state must lie slightly above the 169-keV level ($170 \mathrm{keV}lEl183 \mathrm{keV}$). To the extent that they overlap, both our experimental results and our theoretical conclusions are in agreement with the other two pertinent studies that have been conducted concurrently on ${\mathrm{W}}^{188}$ and ${\mathrm{Re}}^{188m}$ by Roy and by Takahashi, McKeown, and Scharff-Goldhaber. For the purpose of this report, the energy of 171.5 keV for the isomeric state, directly observed by the latter authors, is assumed to be the best value. The ground state and five excited states are assigned the following spins: ground state, $I={1}^{\ensuremath{-}}$; 63.7 keV, $I={2}^{\ensuremath{-}}$; 156.5 keV, $I={3}^{\ensuremath{-}}$; 169.6 keV, $I={3}^{\ensuremath{-}}$; 171.5 keV, $I={6}^{\ensuremath{-}}$; and 290.3 keV, $I={1}^{\ensuremath{-}}$. An interpretation of the level scheme is presented in terms of the spin-spin coupling model for odd-odd nuclei proposed by Gallagher and Moszkowski. All of the observed levels can be explained by various couplings of a proton in the ${\frac{5}{2}}^{+}$ [402] Nilsson level to a neutron in one of three different available neutron levels. The first two excited states are interpreted as members of a $K=1$ rotational band based on the ground state.