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Small-angle particle–particle correlations were measured in the two matching reactions 280 MeV 40Ar + 27Al and 670 MeV 55Mn + 12C. These two reactions were used to produce the composite nucleus, 67Ga*, at the same initial excitation energy of 127 MeV, but with different entrance channel angular momentum distributions. A simple trajectory model was used to compute the average emission times between various particle pairs, and comparisons with the data show that there is a significant difference in the deexcitation of the composite nucleus formed from the two reactions. Statistical model calculations were compared to the experimental observations with the added constraint that the model input parameters were consistent with those derived from observed charged-particle energy spectra and angular distributions. It was found that the calculated correlation functions were insensitive to the input spin distributions, but agreed fairly well with the data from the lower-spin system. The higher-spin reaction data were poorly reproduced by the calculations.

Using thick-target, thick-catcher recoil range techniques, target residues from the interaction of copper with 40 MeV/nucleon [sup 14]N, 35 MeV/nucleon [sup 16]O, and 25 MeV/nucleon [sup 22]Ne have been studied. Isobaric and mass yield distributions as well as longitudinal momentum transfer information have been determined from measured cross section, average forward range, and forward-to-backward ratios. Comparisons with previously reported reactions involving copper and lighter ions have been made. Comparisons of the data with the interaction-evaporation model Boltzmann-Vehling-Uhlenbeck-PACE are presented.

Target residues from the interaction of copper with 90 MeV/nucleon [sup 6]Li ions have been studied utilizing thick-target, thick-catcher recoil range techniques. Cross sections, average forward ranges, and forward-to-backward ratios have been measured. Isobaric and mass yield distributions have been constructed from the cross section data. Longitudinal momentum transfer information has been obtained. Comparison with a variety of lighter and heavier projectiles interacting with copper have been made. Comparisons of the data with initial interaction-evaporation models ISABELLE-EVA, BUU-GEMINI, and BUU-PACE are presented.

Exclusive measurements of light-charged-particle (1H,2H, and 4He) energy spectra, angular distributions, and emission multiplicities are reported for the two reactions 40Ar+27Al and 55Mn+12C at a matched excitation energy of 127 MeV. Comparisons are made with statistical model predictions for the evaporative processes in these reactions, which can be characterized as emissions from rotational-energy-dominated systems. The model simulations do well in reproducing a broad range of angular distribution data and the 4He/1H cross-section ratio, using spin distributions derived from fusion cross-section systematics. The same model parameters, however, predict particle energy spectra and coincidence cross sections which are inconsistent with the measurements for both reactions. These results support previous conclusions from model comparisons with inclusive data, and suggest fundamental flaws in the statistical model as applied to light-mass, high-spin, nuclear systems.

In order to test the statistical model’s ability to predict the behavior of relatively light mass systems (A≈67) with large angular momenta, two matched heavy ion nuclear reactions were used to produce 67Ga* composite nuclei at an excitation energy of 127 MeV. Light charged particles (protons, deuterons, tritons, and α particles) were used as probes to characterize the composite systems and track the deexcitation processes. From these measurements, energy spectra, cross sections, angular distributions, anisotropy ratios, and particle multiplicities were deduced. Measuring many degrees of freedom provides a stringent test for the statistical models. What is found is that models which did well in predicting the behavior of heavy composite systems (A≈150), are unable to simultaneously reproduce energy spectra, angular distributions, and particle multiplicities for the lighter systems (A≈67), where angular momentum plays a dominant role. This implies that more rigorous models and/or additional physics are needed to understand the behavior of the hot, high-spin nuclear matter in this mass region.

E896 has measured Lambda production in 11.6A GeV/c Au-Au collisions over virtually the whole rapidity phase space. The midrapidity p(t) distributions have been measured for the first time at this energy and appear to indicate that the Lambda hyperons have different freeze-out conditions than protons. A comparison with the relativistic quantum molecular dynamics model shows that while there is good shape agreement at high rapidity the model predicts significantly different slopes of the m(t) spectra at midrapidity. The data, where overlap occurs, are consistent with previously reported measurements.

E896 has measured Lambda production in 11.6A GeV/c Au-Au collisions over virtually the whole rapidity phase space. The midrapidity p(t) distributions have been measured for the first time at this energy and appear to indicate that the Lambda hyperons have different freeze-out conditions than protons. A comparison with the relativistic quantum molecular dynamics model shows that while there is good shape agreement at high rapidity the model predicts significantly different slopes of the m(t) spectra at midrapidity. The data, where overlap occurs, are consistent with previously reported measurements.

There are many experimental observables whose measurement can provide information on evaporative particle emission from highly excited composite nuclei. Simultaneous observations of several degrees of freedom in such hot systems allows a stringent test of theoretical models by requiring that the calculations reproduce the multiple characteristics with a unique set of model input parameters. We make such comparisons for two data sets, one involving a relatively heavy (high Z) system and the other referring to a relatively light (low Z) system. For the former case, reasonably good agreement is achieved between statistical model calculations and experimental data, whereas for the latter example, significant inconsistencies are found.