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Neutron fluences were measured from 435 MeV/nucleon Nb ions stopping in a Nb target and 272 MeV/nucleon Nb ions stopping in targets of Nb and Al for neutrons above 20 MeV and at laboratory angles between 3 degrees and 80 degrees. The resultant spectra were integrated over angles to produce neutron energy distributions and over energy to produce neutron angular distributions. The total neutron yields for each system were obtained by integrating over the angular distributions. The angular distributions from all three systems are peaked forward, and the energy distributions from all three systems show an appreciable yield of neutrons with velocities greater than the beam velocity. Comparison of the total neutron yields from the two Nb + Nb systems suggests that the average neutron multiplicity decreases with decreasing projectile energy. Comparison of the total yields from the two 272 MeV/nucleon systems suggests that the total yields show the same dependence on projectile and target mass number as do total inclusive neutron cross sections. The data are compared with Boltzmann-Uehling-Uhlenbeck model calculations.

Impact-parameter filtered longitudinal and transverse two-proton correlation functions measured for 36Ar+ 45Sc collisions at [ital E]/[ital A]=80 MeV are compared to predictions of the BUU transport model. For a cut on large transverse energies, the overall trends of the measured correlated functions are rather well reproduced by calculations for central collisions. Systematic discrepancies become visible, however, for calculations with larger impact parameters.

Velocity distributions and fragment-fragment correlation functions have been measured as a function of charged particle multiplicity for $^{129}\mathrm{Xe}$${+}^{\mathrm{nat}}$Cu collisions at E/A=50 MeV. With increasing multiplicity, the velocity distributions evolve from a pattern exhibiting targetlike and projectilelike sources to an anisotropic distribution centered near the projectile-target center-of-mass velocity. Emission times extracted from the correlation functions are consistent with the decay of a projectilelike source in low multiplicity collisions, but the time scale for fragment emission in the high multiplicity collisions is too short for a separation of sources to occur.

Collisions between $^{36}\mathrm{Ar}$ projectile and $^{197}\mathrm{Au}$ target nuclei at E/A=35 MeV have been studied with the Michigan State University Miniball, a 4\ensuremath{\pi} phoswich array with a low detection threshold. Azimuthal distributions of charged particles with respect to the reaction plane are determined via the transverse-momentum-tensor method. Dependence on the kinetic energy of the emitted particles, the collision geometry, and the associated charged particle multiplicity is investigated. Corrections for the intrinsic resolution of the experimental reaction plane determination are applied. Scaling implied by the coalescence model is explored and the data are compared to the results of microscopic calculations within the Boltzmann-Uehling-Uhlenbeck theory.

Element distributions and fragment multiplicity distributions have been measured for E/A=50 MeV $^{129}\mathrm{Xe}$${+}^{12}$C, $^{27}\mathrm{Al}$, $^{51}\mathrm{V}$, $^{\mathrm{nat}}\mathrm{Cu}$, $^{89}\mathrm{Y}$, and $^{197}\mathrm{Au}$ reactions using a low threshold 4\ensuremath{\pi} detector. Both distributions show a strong correlation with the detected charged particle multiplicity and a large degree of target independence. The measured distributions are compared with hybrid model calculations which incorporate important dynamical aspects in both the preequilibrium and statistical emission phases. Results of these calculations are in reasonable agreement with the data. However, uncertainties with regard to the compressibility of nuclear matter remain due to uncertainties in the coupling of the two models.

An analysis of charged particle distributions is performed to search for large fluctuations and signals of intermittency in 36 Ar + 197 Au reactions at E/A=35–110 MeV. When the effects of impact-parameter averaging are reduced by appropriate cuts on the total transverse energy, charged particle multiplicity distributions narrower than Poisson distributions are observed. Such distributions are inconsistent with intermittency signals of non-trivial origin.

Relative abundances of intermediate mass fragments and light particles measured for 36 Ar+ 197 Au collisions at E A = 50, 80 and 110 MeV lie within the range of percolation model predictions, but for 129 Xe+ 197 Au collisions at E A = 50 MeV , the percolation model predicts too small admixtures of intermediate mass fragments among the emitted charged particles.

Multifragment emission in the reaction 36 Ar + 197 Au at E A =35, 80, and 110 MeV has been measured with a low-threshold 4π detector array. Over this broad range of incident energies, the mean values and variances of the intermediate mass fragment (IMF: 3 ⩽ Z ⩽ 20) multiplicity distributions exhibit an approximate scaling with the total charged particle multiplicity. The measured multiplicities of light charged particles and intermediate mass fragments are compared with both a model involving statistical decay of an expanding compound nucleus, and with a model involving microscopic quasi-particle dynamics. The statistical decay model predictions are sensitive to the low-density nuclear equation of state.

Multifragment disintegrations following $^{129}\mathrm{Xe}$${+}^{197}$Au collisions at E/A=50 MeV have been studied with a multidetector system covering 88% of 4\ensuremath{\pi} in solid angle. The average number of intermediate-mass fragments (Z=3--20) increases strongly as a function of charged-particle multiplicity and reaches values larger than six for the most violent collisions. The results are compared to calculations with both dynamical and statistical models.

A compact and highly granular charged particle detection array, covering 89% of 4π in solid angle, is described. In its present configuration, the array consists of 188 fast-plastic CsI(Tl) phoswich detectors arranged in 11 rings coaxial about the beam axis. Each phoswich detector is comprised of a 40 μm thick plastic scintillator foil and a 2 cm thick CsI(Tl) crystal selected for good scintillation uniformity. The detectors are read out by photomultiplier tubes. Elemental identification up to Z ≈ 18 and isotopic identification of H and He nuclei is achieved by exploiting pulse shape discrimination techniques.

Intermediate-mass-fragment (IMF, 3 {le} Z {le} 20) emission probabilities and IMF charge distributions were recently shown to be reducible to the corresponding one fragment quantities. Furthermore, a strong thermal scaling was shown to control the energy dependence of the same quantities. The multifragmentation scenario painted by these experimental observations is that of a process controlled by a largely independent emission of individual fragments, which, in turn is dominated by phase space. Fragment-fragment angular correlations have been used to study the space-time extension of the emitting source. In particular, small angle repulsion (the Coulomb hole) has been interpreted in terms of the Coulomb repulsion of fragments emitted near each other, both in space and time. We will show in this paper that, except at small angles, the particle-particle angular correlations and their dependence on excitation energy are interpretable in terms of nearly independently emitted fragments whose angular distributions are controlled by phase space. Thus we show that the angular correlations are reducible and thermally scalable. A mass scaling of the angular correlations will also be demonstrated and its possible implications discussed.

The production of high-energy photons in an intermediate energy heavy-ion reaction (65 MeV/nucleon $^{40}\mathrm{Ar}$${+}^{93}$Nb) is studied by characterizing the events, which produce the photons, by the forward and backward, light and heavy, charged particle production. While the absolute yield of high-energy photons increases with increasing charged particle multiplicity, the spectral shape is found to be almost independent of multiplicity. This indicates that the fundamental photon production mechanism is insensitive to the impact parameter but that the production process is more probable for the more violent collisions. This is expected for an incoherent nucleon-nucleon bremsstrahlung mechanism but not for a statistical mechanism. This work also provides a comparison of two observables that have been suggested as impact parameter selectors: the high-energy photon yield and the charged particle multiplicity. We find that the photon yield, binned by particle multiplicity, does not scale as would be expected if both techniques truly measured the impact parameter. This observation can be explained by large fluctuations in the particle multiplicity at fixed impact parameter.

Two-particle correlations at small relative momenta were measured for /sup 16/O-induced reactions on /sup 197/Au at E/A = 94 MeV, providing information about the space-time localization and excitation energy density of the emitting system. Two-particle correlation functions suggest that emission occurs from a region which is slightly larger than observed for /sup 14/N-induced reactions at E/A = 35 MeV, but significantly smaller than for /sup 40/Ar-induced reactions at E/A = 60 MeV. In contrast, the relative populations of widely separated particle unbound states are found to be surprisingly independent of incident energy and projectile mass.

The dependence of multifragment-emission processes upon linear momentum transfer to the target residue is determined for /sup 36/Ar-induced reactions on /sup 238/U at /ital E///ital A/=35 MeV. Significantly more intermediate-mass fragments are emitted in central collisions. Multiplicity distributions for intermediate-mass fragments emitted behind the grazing angle resemble Poisson distributions and are consistent with a stochastic production process. Exit channels with up to five intermediate-mass fragments and two fission fragments were observed.

The relation between charged-particle multiplicity and linear momentum transfer to heavy reaction residues has been investigated with a 4π charged-particle detector for the reactions 36Ar+238U at E A =35 MeV and 14N+238U at E A =50 MeV . The multiplicity of charged particles at backward angles (θ > 35°) incrreases linear momentum transfer while the multiplicity of charged particles in the forward direction is almost independent of the linear momentum transfer.