Prompt light particle emission in the 36Ar + 58Ni reaction at 95 MeV/nucleon

The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function of impact parameter. The results are compared with experimental data from the ³⁶Ar + ⁵⁸Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity. Received: 27 July 2000 / Accepted: 20 November 2000     

Sequential emission of neutrons in the reaction16O+64Ni at 7.5–12 MeV per nucleon

Neutron energy and angular distributions have been studied in coincidence with projectilelike fragments (PF) for quasielastic and deeply inelastic collisions of¹⁶O on⁶⁴Ni at 7.5–12 MeV/u bombarding energy. The neutron yield can be explained assuming only two isotropically emitting sources:i) sequential emission from fully accelerated PF andii) evaporation from fully accelerated targetlike fragments (TF). ForZ=6 andZ=8 ejectiles known excited states in¹³C and¹⁷O could be identified. For oxygen, this suggests a direct excitation process,n pickup from the target. No significant evidence for preequilibrium neutron emission was found even at the highest bombarding energy. The TF temperatures and neutron multiplicities are consistent with the assumption that thermal equilibrium was reached during the binary reaction.     

Incomplete deep-inelastic scattering in20Ne+197Au collisions at 20 MeV/nucleon

Correlations between emission angles and energies of coincidentα-particle projectile-fragment pairs have been measured for the²⁰Ne+¹⁹⁷Au system at 390 MeV beam energy. Theα-particles observed close to the direction of the projectile-like fragment were found to result essentially from sequential projectile decay. Starting from the close-geometry data, the contribution of sequentially emittedα-particles was calculated by Monte Carlo simulations for the entire angular range. For deep inelastic events, the measured angular correlations exhibit a spectacular excess over the calculated correlation. This excess is centred close to the beam direction but on the opposite side of it with respect to the detected projectile-like fragment. The correspondingα-particles have velocities around 85% of the projectile velocity indicating emission in an early reaction phase.     

Correlations between fission fragments and light charged-particles in the reaction20Ne+197Au at 13 MeV/nucleon

rgy of light charged-particles has been measured in coincidence with one or two fission fragments in the reaction²⁰Ne+¹⁹⁷Au at a bombarding energy of 13 MeV/u. The fission cross section was found equal to 1,340±260 mb. Assuming that it represents the totality of the fusion cross section, the critical valuel _c is deduced equal to 93±9?, higher thanl _Bf=0=74 in the rotating liquid drop model. The main emission source for protons and alpha particles seems to be a thermally equilibrated composite system. The competition between fission and charged particle emission is unexpected in the frame of the statistical treatment. A high energy component is observed in the forward direction. These results correspond to the first step of a study programme on the evolution of nucleus-nucleus collisions between 10 and 100 MeV per nucleon.     

Data on light-fragment correlations in 40 Ar + 58 Ni at 77 MeV/nucleon

Results of the experimental study of p ⁴ He, d ³ He, dT, pT, p ³ He and, for the first time, nT, n ³ He, n ⁴ He correlations in the region of small relative momenta are presented. The data analysis provides an estimate of the effective source size or emission time.Received: 26 May 2003, Published online: 2 December 2003PACS: 25.70.Pq Multifragment emission and correlations     

The study of neutral pion azimuthal distribution in 58Ni+58Ni reaction at 2 GeV/nucleon

In order to study the anisotropic azimuthal emission of mesons in heavy ion collisions we measured the neutral pions emitted in the Ni+Ni collisions at 2 GeV/u with respect to the reaction plane. We studied the strength of the azimuthal anisotropy for neutral pions in dependence of the transverse momentum and impact parameter. The preliminary results and their comparison with previous experimental data are reported.     

Proton, deuteron, and triton emission in 14N+Ag interactions at an energy of 52 MeV per nucleon

The inclusive energy spectra and multiplicities of p, d, and t from the reactions ¹⁴N(Ag, X), X=p, d, t at E/A=52 MeV are measured. The experimental data are compared with the results obtained within the Dubna version of the cascade model and are analyzed on the basis of the moving-source model.     

Search for high excitation energy structures in the 20Ne + 208Pb system at EA = 30 MeV

The inelastic scattering of 600 MeV ²⁰Ne from ²⁰⁸Pb has been reinvestigated. Cross sections for giant resonance excitation have been extracted and analysed in terms of DWBA. No evidence has been found for higher excitation energy structures.     

Decay of primary ejectiles by light particles and complex fragments emission in20, 22Ne+93Nb reactions at 30 MeV/Nucleon

The observation of projectile-like fragments with an energy corresponding to the beam velocity turns out to be mostly explained by the break-up of the projectile, the break-up of the ejectile formed by transfer and the decay of the excited projectile. The analysis of two kinds of correlations, light particle-projectile-like fragment and fragment-fragment, is an adequate tool to distinguish the different processes. Significant differences are observed related to the structures of the two projectiles (²⁰Ne and²²Ne).     

Heavy fragments emission in the 84Kr on 12C reaction at 35 MeV/nucleon

Heavy residues of collisions of ⁸⁴Kr + ¹²C at 35 MeV/amu were measured using time of flight ΔE?E telescopes. An important part of the total cross section leads to events that have all the characteristics of an equilibrated composite system decaying by heavy fragment emission. The experimental yields are well reproduced using a statistical model.     

Evaporation residue cross sections for 40Ca + 48Ti at 25.0 and 33.9 MeV per nucleon

The fusion and subsequent decay of the system ⁴⁰Ca+⁴⁸Ti has been studied at 25.0 and 33.9 MeV per nucleon bombarding energies. Heavy residues were detected in coincidence with light particles, and evaporation residue cross sections have been extracted. Light particle distributions are well described by a simple kinematical model, and from this the average excitation energies of the system were determined.     

Determination of theQ-value dependence of charged particle emission in the40Ca+40Ca reaction at 10 MeV/nucleon

An iterative method for the determination of the charged particle loss as a function of the reactionQ-value is developped. The analysis is based on experimental data resulting from 400 MeV⁴⁰Ca+⁴⁰Ca collisions.Z distributions are obtained at different calculatedQ-values corrected for evaporation and show rather good agreement — in the strongly damped case — with the ones derived from the OVERLAID ALICE code. Mean numbers of evaporated particles exhibit a linear increase as a function of these correctedQ-values; this corresponds to the evolution from quasi-direct to fully relaxed reactions.     

Neutral pion production at 350 MeV/u in the system20Ne +27Al

π⁰ -production probability of (9± 2)· 10^{? 3} per²⁰Ne+Al reaction has been measured at 350 MeV/u using the Two Arm Photon Spectrometer TAPS. This yield is consistent with an interpolation of published π-production rates in heavy ion collisions.     

Alpha particles from the reaction12C +12C at 28.7 MeV/nucleon

A classical dynamical alpha-cluster model has been developed and applied in order to get inclusive energy spectra of alpha particles produced in the collision of¹²C +¹²C at the beam energy 28.7 MeV/A. Results of the calculations are compared with experimental data. The shapes of the experimental energy spectra and the absolute normalization at forward angles are approximately described without any free parameters. The model makes it possible to distinguish alpha particles originating from the compound system and from direct processes. The spectra at forward angles are dominated by projectile fragmentation processes. The cross section at larger angles is overestimated, which is partially due to emission of particles other than alpha particles in central collisions. The evaporation Hauser-Feshbach model predicts that alpha particles emitted from the compound nucleus constitute less than 26% of all emitted particles.     

Intrinsic fragment spins generated in the reactions of 20Ne with 197Au and 238U at 12.6 MeV/nucleon

The average magnitude and alignment of the intrinsic spin of the heavy partner from the reaction of 252 MeV ²⁰Ne with ¹⁹⁷Au and ²³⁸U were determined as a function of Q-value. These spin values were extracted from sequential fission angular distributions obtained in coincidence with projectile-like products. For all Q-values a large out-of-plane anisotropy was observed, while for large negative Q-values an in-plane anisotropy was observed. A very large entrance-channel mass-asymmetry was chosen to provide a stringent test of equilibrium statistical model predictions for the spin alignment. The importance of determining the direction of the line-of-centers of the dinuclear system at scission is discussed. Large values of P_ZZ were deduced for all Q- values. P_XY was observed to be positive in the quasielastic region and negative in the deep-inelastic region. The extracted alignment data are compared to equilibrium statistical model calculations.     

Evidence of non-statistical structures in the elastic and inelastic scattering of58Ni+58Ni and58Ni+62Ni and intermediate dinuclear states

Excitation functions and angular distributions of⁵⁸Ni+⁵⁸Ni and⁵⁸Ni+⁶²Ni scattering at energies just above the Coulomb barrier have been measured aroundθ _cm=90° in energy stepsΔE _cm=0.25 MeV fromE _cm ? 110 MeV toE _cm ? 120 MeV for⁵⁸Ni+⁵⁸Ni and fromE _cm ? 110 MeV toE _cm ? 118 MeV for⁵⁸Ni+⁶²Ni. Evidence for structure of non-statistical character has been found in the angle-summed excitation functions; this evidence is corroborated by the analysis of the angular distributions. This is the first time that non-statistical structure in elastic and inelastic scattering is reported with high confidence level for this mass and excitation energy ranges. Attempts are presented to understand the nature of this structure, including the presence of intermediate dinuclear states and virtual states in a potential well.