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In the reaction 3 He (1.8 GeV) + nat Ag , events are observed with a heavy fragment (HF), A≥10 , in coincidence with charged particles detected over 70% of 4π solid angle. Calorimetric measurements show high thermal excitation energies of the target primary fragment: 6–8 MeV per nucleon for HF mass ≳45 . For these excitation energies, the probability for having an evaporative residue is shown to be unexpectedly high when compared with current multifragmentation models. This result is interpreted as linked to the use of light ion projectiles at relatively low incident energy.

Multifragmentation studies with GeV light-ion beams indicate that for the most violent collisions, complex fragments are emitted during expansion of the hot source, followed by near simultaneous breakup of the system near ρ/ρ 0 ∼ 1/3. The results are compared with hybrid INC/EES and INC/SMM models. Preliminary data for the 8 GeV/c π − and preactions on 197 Au show enhanced deposition energy for the antiproton beam.

The charge-moment technique has been used to study the fragment charge distribution for the {sup 3}He(4.8thinspGeV)+{sup 197}Au reaction. A large variety of fragment charges characterized by a relative variance {approximately}2.3, is observed for excitation energies around 5.5 MeV/nucleon. Similar signals related to a phase transition are predicted by the percolation model and the statistical multifragmentation model. Effects of detector acceptance and contribution from fission are discussed. {copyright} {ital 1998} {ital The American Physical Society}

Exclusive studies of sideways-peaked angular distributions for intermediate-mass fragments (IMFs) produced in hadron-induced reactions have been performed with the Indiana silicon sphere (ISiS) detector array. The effect becomes prominent for beam momenta above about 10thinspGeV/c. Both the magnitude of the effect and the peak angle increase as a function of fragment multiplicity and charge. When gated on IMF kinetic energy, the angular distributions evolve from forward peaked to nearly isotropic as the fragment energy decreases. Fragment-fragment correlation studies show no evidence for a preferred angle that might signal a fast dynamic breakup mechanism. Moving-source and intranuclear cascade simulations suggest a possible kinematic origin arising from significant transverse momentum imparted to the recoil nucleus during the fast cascade. A two-step cascade and statistical multifragmentation calculation is consistent with the data. {copyright} {ital 1998} {ital The American Physical Society}

Reactions of 1.8 – 4.8 GeV 3He, 5.0 – 9.2 GeV/c π− and 6.0 – 14.6 GeV/c protons with natAg and 197Au targets have been studied with the ISiS 4π detector array. From reconstructed events, excitation-energy distributions have been determined and combined with a 2,3H3,4He isotope-ratio thermometer to study the heating curve for the thermal-like component of these reactions. Dynamic effects also manifest themselves in the data, as evidenced by deposition-energy saturation above ∼5 GeV, IMF emission during expansion, and sideways peaking of the IMF angular distributions for beam energies Eb ≥ 10 GeV.

The first 4π studies of identified light-charged-particles and IMFs emitted in the p, π − + 197 Au reactions above 5 GeV/c are reported. Multiplicity and angular distributions show little sensitivity to either bombarding energy or projectile type. Excitation energy distributions obtained from data for the 4.8 GeV 3 He + 197 Au reaction yield values up to E ∗ ≲ 1500 MeV and E ∗ A residue ≲ 10 MeV/nucleon . Analysis of large-angle, IMF-IMF correlations for this same system suggests that multifragmentation is a fast, time-dependent process.

4{pi} studies of multiple charged-particle emission in GeV {pi}{sup {minus}} - and proton-induced reactions on a Au target have been performed with the ISiS detector array. Multiplicity, charge, and angular distributions yield nearly identical results for both p and {pi}{sup {minus}} beams, suggesting an independence of hadron type in initiating the fast cascade and subsequent energy deposition in the struck nucleus. The excitation functions show little sensitivity to beam momentum, consistent with a saturation in deposition energy and the concept of limiting fragmentation. However, the intermediate mass fragment multiplicities and fragment charge distributions depend strongly on collision violence. {copyright} {ital 1997} {ital The American Physical Society}

The Indiana Silicon Sphere 4{pi} detector has been used to measure light-charged particles and intermediate-mass fragments (IMFs) emitted in the 18{endash}4.8 GeV {sup 3}He+{sup nat}Ag, {sup 197}Au reactions. Ejectile multiplicity and total event kinetic energy distributions scale systematically with projectile energy and target mass, except for the {sup nat}Ag target at 3.6 and 4.8 GeV. For this system, a saturation in deposition energy is indicated by the data, suggesting the upper projectile energy for stopping has been reached. Maximum deposition energies of {approximately}950 MeV for the {sup nat}Ag target and {approximately}1600 MeV for the {sup 197}Au target are inferred from the data. The results also demonstrate the importance of accounting for fast cascade processes in defining the excitation energy of the targetlike residue. Correlations between various observables and the average IMF multiplicity indicate that the total thermal energy and total observed charge provide useful gauges of the excitation energy of the fragmenting system. Comparison of the experimental distributions with intranuclear cascade predictions shows qualitative agreement. {copyright} {ital 1996 The American Physical Society.}

A low threshold charged particle detector array for the study of fragmentation processes in light-ion-induced reactions has been constructed and successfully implemented at the IUCF and Saturne II accelerators. The array consists of 162-triple-element detector telescopes mounted in a spherical geometry and covering 74% of 4π in solid angle. Telescope elements are composed of (1) an axial-field gas ionization chamber operated with C3F8 gas; (2) a 0.5 mm thick passivated silicon detector, and (3) a 2.8 cm thick CsI(Tl) scintillation crystal with photodiode readout. Discrete element identification is obtained for ejectiles up to Z ∼ 16 over the dynamic range 0.7 ≤ EA ≤ 95 MeV/nucleon. Isotopes are also distinguished for H, He, Li and Be ejectiles with 8 ≲ EA ≲ 95 MeV. Custom-designed electronics are employed for bias supplies and linear signal processing. Data are acquired via a CAMAC/VME/Ethernet system.

Multifragmentation of ${}^{\mathrm{nat}}$Ag and ${}^{197}$Au nuclei induced by a 4.8-GeV${\mathrm{}}^{3}$He ions has been studied with the Indiana Silicon Sphere $4\ensuremath{\pi}$ detector array. Rapidity and moving source analyses are consistent with thermal emission from a source in approximate kinetic equilibrium. For the most dissipative collisions, the spectral Coulomb peaks are broadened to very low energies, indicative of emission from an extended nuclear system. Predictions of a model with an intranuclear cascade and an expanding, emitting source compare well with experimental multiplicity distributions and the evolution of fragment spectral shapes.

Intermediate-mass fragments formed in reactions of $^{3}\mathrm{He}$ ions with $^{\mathrm{nat}}\mathrm{Ag}$ and $^{197}\mathrm{Au}$ targets have been studied at five energies between 0.48 and 3.6 GeV. Inclusive measurements show that as the bombarding energy increases, there is a strong enhancement in fragment cross sections and a trend toward isotropic angular distributions. Between 0.90 and 1.8 GeV, a change in the emission mechanism is suggested by (1) kinetic energy spectra with high-energy tails that become distinctly flatter, (2) a broadening of the spectral Coulomb peaks toward lower energies, and (3) charge distributions that become constant, exhibiting a power-law exponent \ensuremath{\tau}\ensuremath{\approxeq}2.0. Exclusive studies of the $^{3}\mathrm{He}$${+}^{\mathrm{nat}}$Ag system at 0.90 and 3.6 GeV detected multifragment events with multiplicities up to four. The probability for high-multiplicity events increases about 40-fold between 0.90 and 3.6 GeV. At both energies, the kinetic energy spectra depend on multiplicity, especially when triggering on backward-emitted fragments. For multiplicity three events, a rapidity analysis of the data at 3.6 GeV is consistent with a single, relatively low source velocity, ${\mathit{v}}_{\mathit{S}}$\ensuremath{\approxeq}0.4 cm/ns. The data are compared with predictions of a coplanarity-sphericity calculation, the sequential statistical decay code GEMINI, and a hybrid intranuclear cascade/percolation model.

Multifragment events for intermediate-mass fragments (3{le}{ital Z}{le}12) with multiplicity up to four have been observed in the reaction of 0.90 and 3.6 GeV {sup 3}He ions with {sup natAg} nuclei. Fragment energy spectra and angular distributions are found to be dependent on event multiplicity. The data suggest significant modification of the Coulomb field of the emitting source.

An extensive study of GeV light-ion-induced multifragmentation and its possible interpretation in terms of a nuclear liquid-gas phase transition has been performed with the Indiana Silicon Sphere (ISiS)4 pi detector array. Measurements were performed with 5-15 GeV/c p, pbar, and pion beams incident on $^{197}$Au and 2-5 GeV $^3$He incident on $^{nat}$Ag and $^{197}$Au targets. Both the reaction dynamics and the subsequent decay of the heavy residues have been explored. The data provide evidence for a dramatic change in the reaction observables near an excitation energy of E*/A = 4-5 MeV per residue nucleon. In this region, fragment multiplicities and energy spectra indicate emission from an expanded/dilute source on a very short time scale (20-50 fm/c). These properties, along with caloric curve and scaling-law behavior, yield a pattern that is consistent with a nuclear liquid-gas phase transition., Comment: 67 pages, 44 figures, all included in tar file

Multifragment breakup of $^{\text{nat}}\mathrm{Ag}$ and $^{197}\mathrm{Au}$ nuclei bombarded by $1.8--4.8\phantom{\rule{0.3em}{0ex}}\text{GeV}$ $^{3}\mathrm{He}$ ions has been studied with the Indiana Silicon Sphere $4\ensuremath{\pi}$ detector array. To investigate the properties of the emitting source as a function of excitation energy, a two-component moving-source analysis has been performed on the intermediate-mass-fragment spectra, gating on excitation energy. The results provide evidence for nuclear expansion∕dilution to a value of $\ensuremath{\rho}∕{\ensuremath{\rho}}_{0}\ensuremath{\lesssim}1∕3$ prior to breakup. For the most violent events, relatively low source velocities of $v∕c~0.01$ and slope temperatures of $T\ensuremath{\sim}15\phantom{\rule{0.3em}{0ex}}\text{MeV}$ are obtained for the dominant thermal-like source. The dependence of isotope ratios on deposition energy and ejectile kinetic energy is examined for H and He isotopes, and the caloric curves for the $4.8\phantom{\rule{0.3em}{0ex}}\text{GeV}$ data are presented.

A detector system has been developed for the purpose of detecting low energy recoil particles in coincidence. The system comprises four silicon double-sided strip detectors (DSSDs) employing ASIC-based readout. The readout scheme is self-triggering, and the use of programmable lookup units (PLUs) makes it possible to trigger on two-particle coincidences, even if the two particles are incident on the same detector. This detector system is the key component of the tagged neutron facility under development at the Indiana Cooler.

Operating characteristics of the Indiana Silicon Sphere 4 π detector array are outlined. The detector geometry is spherical, with 90 telescopes in the forward hemisphere and 72 at backward angles, covering a total solid angle of 74% of 4π. Each telescope consists of a simple gas-ion chamber, operated with C3F8 gas, followed by a 0.5 mm thick ion-implanted silicon detector and a 28 mm CsI(Tl) crystal, readout by a photodiode. Custom-built bias supplies and NIM preamp/shaper modules were used in conjunction with commercial CFD, TDC and ADC CAMAC units.

To investigate the source size and time dependence of multifragmentation reactions, small- and large-angle relative velocity correlations between coincident complex fragments have been measured for the 1.8[endash]4.8 GeV [sup 3]He+[sup nat]Ag, [sup 197]Au systems. The results support an evolutionary scenario for the fragment emission process in which lighter IMFs (Z[approx lt]6) are emitted from a hot, more dense source prior to breakup of an expanded residue. For the most highly excited residues, for which there is a significant yield of fragments with very soft energy spectra (E/A[le]3 MeV), comparisons with an [ital N]-body simulation suggest a breakup time of [tau][approximately]50 fm/c for the expanded residue. Comparison of these data with both the evolutionary expanding emitting source model and the Copenhagen statistical multifragmentation model shows good agreement for heavier IMF[close quote]s formed in the final breakup stage, but only the evolutionary model is successful in accounting for the lighter IMFs. thinsp [copyright] [ital 1999] [ital The American Physical Society]

For light-ion-induced reactions in the bombarding energy regime 1–10 GeV, dramatic changes occur for inclusive observables associated with highly excited heavy residues.1 For example, the excitation functions for IMF production (IMF: 3 ≤ Z ≥ 15) increase by more than two orders of magnitude over this energy range-while the N-N total scattering cross section changes only gradually. This has been interpreted in terms of large deposition energies in the residue, giving rise to multifragmentation events. Subsequent 4π studies2 have verified this interpretation and further shown that the most highly excited residues are produced with very low velocities (v/c ∼ 0.01). This latter fact suggests the importance of baryonic resonances in the excitation process; the former demonstrates that light-ion-induced reactions create hot, multifragmenting systems that can be observed in the laboratory with minimal kinematic distortion.

The subject of hot nuclei draws a number of engaging problems. Broadly speaking one can divide the interest into three; the heating dynamics 1–3; properties of hot nuclear matter 4 and the decay processes 5. All this is within the confines of a relatively small number of nucleons interacting through an interplay of short and long range forces 5. In this contribution we report on a study of hot nuclei, where through an appropriate choice of incident channel and event selection, dynamical effects are attenuated and multifragmentation is limited. Herein, we aim at giving three preparatory results; (i) the 3He(1.8 GeV) + nat Ag can be described using an intranuclear cascade, INC, model; (ii) through a suitable selection of events we give a limit of the excitation energy that a nucleus can absorb without breaking into large pieces; (iii) we show that corresponding alpha decay is consistent with an, evaporative process.

The continuum cross sections and analyzing powers from the $^{2}\mathrm{H}$, $^{3}$,4He(p\ensuremath{\rightarrow},p') and $^{3}$,4He(p\ensuremath{\rightarrow},d') reactions were measured for 98.7 and 149.3 MeV polarized protons in the angular range 17.5\ifmmode^\circ\else\textdegree\fi{} to 60\ifmmode^\circ\else\textdegree\fi{}. The $^{2}\mathrm{H}$ and $^{3}\mathrm{He}$ data show strong quasifree contributions with more ambiguous results for $^{4}\mathrm{He}$. These data are compared with distorted-wave impulse approximation calculations based on quasifree nucleon and deuteron knockout. Overall, the agreement between theory and experiment is moderately good. However, some significant discrepancies are observed and corrections to the simple model are discussed.