Nuclear Levels in 188Re

Nuclear levels in ¹⁸⁸Re have been investigated using the following experimental techniques: measurement of neutron-capture γ-ray transitions with energies between 4.8 and 6.0 MeV using a Ge(Li) pair spectrometer; study of (d,p) spectra using 12-MeV deuterons and a broad-range magnetic spectrograph; measurement of (n,γ) spectra between 45 and 830 keV with a bent-crystal spectrometer; coincidence studies of the (n,γ) radiation using two Ge(Li) detectors, including a study of short-lived isomeric states using delayed-coincidence techniques; and observation of the γ rays following β decay of ¹⁸⁸W using a Ge(Li) detector. A nuclear level scheme for ¹⁸⁸Re has been constructed by combining the results of the above measurements with published data. Information, including spin and parity assignments, is presented on 36 low-lying levels. The lifetimes of five excited states are reported. The Nilsson model has been used to interpret the level structure. Assignments are proposed which involve 15 separate rotational bands. Proposed Nilsson configurations, band-head energies, and band-head lifetimes (if known) are: 1^-[402↑ - 512↓], 0.0 keV; 3^-[402↑ + 510↑], 169.4 keV; 6^-[402↑ + 503↑], 172.1 keV, 19 min; 4^-[402↑ + 512↑], 182.7 keV, 18 nsec; 2^-[402↑ - 505↓], 205.3 keV, 3.2 nsec; 0⁺[514↑ - 505↓], 207.9 keV, 3.2 nsec; 3⁺[514↑ - 512↓], 230.9 keV, 21 nsec; 2^-[402↑ - 510↑], 256.9 keV; 1^-[402↑ + 503↑], 290.7 keV; 4^-[402↑ + 501↑], 325.9 keV; 5⁺[514↑ + 510↑], 360.9 keV, 5.2 nsec; 3⁺[402↑ - 615↑], 439.7 keV; 1⁺[514↑ - 503↑], 482.2 keV; 1^-[402↑ - 501↑], 556.8 keV. A K^π=1^- band, believed to be predominantly a |K-2| γ-vibrational band, is observed at 582.2 keV. The measured (d,p) reaction cross sections are compared with theoretical calculations based on these assignments. The β-decay measurements have revealed a previously unknown β branch from the ¹⁸⁸W ground state to a I^π=0⁺ level at 207.9 keV. This 0⁺ --> 0⁺ transition (ft=9.9) is discussed in terms of isobaric analog state mixing. Results of a calculation which uses a parametrized residual neutron-proton interaction to predict the parallel-antiparallel splitting energies and K=0 even-odd shifts in ¹⁸⁶Re and ¹⁸⁸Re are presented and compared with experiment.