We have investigated the effects of isotopic composition on the band gap of CuCl on a series of samples made out of the stable isotopes 63 Cu, 65 Cu, 35 Cl, and 37 Cl. Besides specimens containing elements with the natural abundances, we have measured samples with monoisotopic sublattices as well as artificial mixtures of isotopes. With nonlinear ͑two-photon absorption, second-harmonic generation͒ and linear ͑luminescence͒ optical spectroscopy we find that the fundamental gap of CuCl increases by 364͑18͒ eV/amu when increasing the Cl mass. However, it decreases by 76͑5͒ eV/amu when increasing the Cu mass. Using a two-oscillator model for the lattice dynamics of CuCl we show that these rates are consistent with the anomalous increase of the band gap with increasing temperature. These effects can be traced back to the strong p-d mixing in the copper halides. From the temperature dependence of the band gap of CuBr we also estimate the changes of its gap with isotopic composition.

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Excited states in 64 Ni, 66 Ni, and 68 Ni were populated in quasielastic and deep-inelastic reactions of a 430-MeV 64 Ni beam on a thick 238 U target. Level schemes including many nonyrast states were established up to respective excitation energies of 6.8, 8.2, and 7.8 MeV on the basis of γ -ray coincidence events measured with the Gammasphere array. Spin-parity assignments were deduced from an angular-correlation analysis and from observed γ -decay patterns, but information from earlier γ -spectroscopy and nuclear-reaction studies was used as well. The spin assignments for nonyrast states were supported further by their observed population pattern in quasielastic reactions selected through a cross-coincidence technique. Previously established isomeric-state decays in 66 Ni and 68 Ni were verified and delineated more extensively through a delayed-coincidence analysis. A number of new states located above these long-lived states were identified. Shell-model calculations were carried out in the p 3/2 f 5/2 p 1/2 g 9/2 model space with two effective interactions using a 56 Ni core. Satisfactory agreement between experimental and computed level energies was achieved, even though the calculations indicate that all the states are associated with rather complex configurations. This complexity is illustrated through the discussion of the structure of the negative-parity states and of the M1 decays between them. The best agreement between data and calculations was achieved for 68 Ni, the nucleus where the calculated states have the simplest structure. In this nucleus, the existence of two low-spin states reported recently was confirmed as well. Results of the present study do not indicate any involvement of collective degrees of freedom and confirm the validity of a shell-model description in terms of neutron excitations combined with a closed Z = 28 proton shell. Further improvements to the calculations are desirable.

The neutron-rich isotopes 65,67 Fe and 65 Co have been produced at the LISOL facility, Louvain-La-Neuve, in the proton-induced fission of 238 U. Beams of these isotopes have been extracted with high selectivity by means of resonant laser ionization combined with mass separation. Yrast and near-yrast levels of 65 Co have also been populated in the 64 Ni+ 238 U reaction at Argonne National Laboratory. The level structure of 65 Co could be investigated by combining all the information from both the 65 Fe and 65 Co β decay and the deep-inelastic reaction. The 65 Fe, 65 Co, and 67 Fe decay schemes and the 65 Co yrast structure are fully established. The 65,67 Co level structures can be interpreted as resulting from the coexistence of core-coupled states with levels based on a low-energy proton-intruder configuration.