Nuclear levels in 192Ir

Levels in Ir-192 were studied using neutron-capture and direct-reaction spectroscopy. A pair spectrometer was used to study the high-energy gamma-ray spectrum from thermal-neutron capture in enriched IR-191 over the energy range 4640-6200 keV. From the same reaction, low-energy gamma-radiation was observed from 48 to 635 keV with semiconductor and curved-crystal spectrometers, conversion electrons were observed from 19 to 280 keV with a magnetic spectrograph and a prompt and delayed gamma-gamma-coincidence experiment was performed using semiconductor and scintillation detectors. The (n(res), gamma(high)) spectrum measurements were performed with 2 and 24 keV neutrons for primary transitions leading to excitation energies from 0 to 1160 keV. The secondary transitions following capture in three discrete resonances were observed. The spin of several parent states could thus be determined by the "population ratio" method. Using 14, 15 and 22 MeV deuterons, Ir-191(d, p) and Ir-193(d, t) high resolution spectra were observed with a magnetic spectrograph. The ground-state spin I = 4 is confirmed from the angular distribution of gamma-rays from oriented nuclei; the data favour a positive parity, in agreement with model analysis of the experimental magnetic moment and with other experimental evidence. A value of 6198.1 +/- 0.2 keV was obtained for the neutron binding energy in Ir-192. A nuclear level scheme deduced for Ir-192 includes 35 levels connected by 120 transitions. Unambiguous spins and parities were determined in a model-independent way for 14 levels, and narrow ranges of possible values were obtained for the others. Part of the results are interpreted in a qualitative way in the framework of the rotor-plus-particle model, suggesting the existence of a few rotational bands. Calculations performed in the framework of the IBFFM model are compared to the experimental results. It is suggested that the 161 keV I = 9 isomeric state has positive parity.