The populations of neutron-unbound states and of bound states in intermediate-mass fragments have been measured at 15°, 31°, and 64° from the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$+Ag reaction at E/A=35 MeV. We did this for eleven neutron-unbound states in seven isotopes whose bound-state populations we were also able to measure. The data are identified in terms of the reaction mechanism producing them, which is either a deep-inelastic mechanism or a quasielastic mechanism. In order to test the assumption that the deep-inelastic data are produced from a thermal source, the unbound-state–bound-state population ratios of deep-inelastic fragments are compared to the predictions of a thermal sequential decay model. Most, but not all, of the deep-inelastic population ratios are fitted with model calculations that assume a source temperature between 2.5 and 3.5 MeV. In the case of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ we were able to measure four deep-inelastic populations, and in the case of ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ we were able to measure three such populations. To further test the assumption of emission from a thermal source, attempts were made to fit all of the populations from each of these two isotopes with the sequential decay model using a single temperature.

The deep-inelastic populations of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ were fitted with a single temperature between 2.5 and 5.0 MeV. The deep-inelastic populations of ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ were not fitted with any temperature. There is enough of the deep-inelastic data that is not fitted with the predictions of a thermal model that the assumption of a thermal source for the production of deep-inelastic fragments may be incorrect, or there may be other effects present which alter the thermal properties of the data. The quasielastic populations in each ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ were also measured and could not be fitted with the model using a single temperature, which is consistent with the assumption of a nonthermal source of production for quasielastic fragments. The dependence of the unbound-state–bound-state population ratio on the fragment kinetic energy shows a difference between the quasielastic and deep-inelastic data. For quasielastic fragments whose mass is near the mass of the beam, the ratio decreases towards zero as the fragment velocity approaches the beam velocity. In contrast, the ratio for half-beam mass quasielastic fragments is constant or only slightly decreasing as the kinetic energy increases. The ratio for deep-inelastic fragments is approximately constant as a function of kinetic energy, independent of fragment mass. The amount of feeding from several neutron-unbound channels into bound states is measured and compared to the sequential decay model. The model successfully predicts the amount of feeding from most of the channels using a source temperature of 2.5 to 4.0 MeV. The effect of feeding both on spectral temperatures and on population temperatures is investigated. We conclude that the effect of feeding on both temperatures, as determined by model calculations, cannot account for the discrepancy in the values between the two.

• Received 10 December 1990

DOI:https://doi.org/10.1103/PhysRevC.43.2318