Few nucleon transfer versus fragmentation in the production of projectile-like fragments in the40Ar+68Zn reaction at 27.6 MeV/nucleon

The isotope distributions, momentum width distributions, and velocities of the projectile-like fragments in the⁴⁰Ar on⁶⁸Zn reaction have been measured at 27.6 MeV/nucleon incident energy. The results show the existence of a fragmentation process well described in the framework of the high energy fragmentation model. However, important contributions from direct nucleon transfer and damped collisions are present.     

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.     

Peripheral reactions induced by 20Ne at 11 and 15 MeV/nucleon

The breakup of ²⁰Ne has been studied in the ²⁰Ne + ⁵⁴Fe reaction at 11 and 15 MeV/nucleon. Singles projectile-like fragments and correlations between projectile-like fragments and α-particles have been measured. The correlations have been analysed in terms of sequential breakup by extensive Monte Carlo simulations. The major part of the data, even at high-excitation energy, can be described by sequential decay. The large contribution of sequential decay to the inclusive yield is confirmed. Strong energy dissipation is observed, which cannot be accounted for by direct transfer or nucleon exchange.     

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.     

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.     

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     

Subthreshold pion production from nucleus-nucleus collisions around 100 MeV/nucleon

Several global variables were tested with the aim to determine the impact parameter in nucleus-nucleus collisions producing pions at incident energies around 100 MeV/nucleon. The experimental set-up includes the MEDEA multidetector, part of which is used as a ⁰ spectrometer, and an additional hodoscope of plastic scintillators to cover very forward angles. A statistical model was used to generate bothinclusive and pion-triggered events. Selection ofwell measured events was made through the measured total parallel momentum. Among the different global variables which were tested, the average parallel velocity was seen to give the best correlation with the impact parameter.     

Nucleon stripping in deuteron-induced spallation reactions at hundreds MeV/nucleon

A nucleon-nucleus dynamics model was developed to investigate the proton-,neutron-,and deuteron-induced reactions at hundreds of MeV/nucleon.In this model,the trajectory of incident nucleon is described by classical mechanics,and the probability of reaction between the nucleon and nucleus is calculated by exponential damping.It is shown that the total reaction cross sections calculated by the model agree in general with the predictions by the CDCC and the experimental data.The model was applied to investigate the nucleon stripping in deuteron-induced reactions and its symmetry energy dependence.     

Heavy ion reactions at 75–100 MeV/nucleon

Energy and momentum component distributions of singly and doubly charged particles in¹⁶O-emulsion nucleus interactions at 75–100 MeV/n are presented. The parallel momentum distributions show larger shifts than at 2 GeV/n, indicating emission from systems with mean velocities ≈0.06 c relative to the parent nuclei. Particles with intermediate rapidities have, on the average, larger transverse momenta than particles with large rapidities. The charged particle multiplicity in peripheral collisions is the same at 0.1, 0.2 and 2 GeV/n, while the difference in multiplicity for central collisions is pronounced.     

高能铁离子在水介质中核反应过程所导致的能量沉积

在银河宇宙射线中,400MeV/nucleon的铁离子通量相对来讲是较高的,400MeV/nucleon的铁离子对空间辐射引起的损伤和辐射剂量有重要的贡献.本文以Geant4为基础,对400MeV/nucleon Fe离子与物质相互作用后通过核反应过程产生的次级碎片进行模拟分析.对铁离子在水中产生的能量沉积和铁离子与水介质发生核反应后产生的次级碎片的能量沉积进行了模拟研究,得到了通过核反应过程产生次级粒子所导致的剂量贡献. 关键词： 能量沉积 剂量 碎片     

Pion production in heavy ion reactions induced by16O and84Kr beams at 60 MeV per nucleon

Low energy ⁺ and ^– production cross sections have been measured in¹⁶O at 65 MeV/u and⁸⁴Kr at 60 MeV/u induced reactions on⁷Li,¹²C,²⁷Al,¹⁰⁸Ag and¹⁹⁷Au. The results are compared with a previous measurement obtained with¹⁶O at 93 MeV/u. Large deviations are observed between light and heavy ion data. At variance with¹⁶O, the ratios ^–/ ⁺ are independent of the target in the Krypton case. A change in the regime of the projectile-target mass scaling of cross-sections is observed with the heaviest projectile.Experiments performed at GANIL facility, F-14032 Caen, France     

Impact parameter study in multiparticle production at 70 GeV/c

This paper presents a study of the experimental lower boundb _L, on the root-mean-squared impact parameter of the multiparticle production in 70 GeV/c p-nucleon interaction. It has been observed that theb _L decreases with increasing final state multiplicity (n) at this fixed energy. The results are in good agreement with those of other authors.The authors would like to thank Prof. K. D. Tolostov of Dubna, U.S.S.R. for kindly supplying the exposed emulsion plates.     

Knockout reaction induced by ~6 He at 61.2 MeV/u

A knockout reaction induced by ⁶He at 61.2 MeV/u was carried out at the HIRFL-RIBLL radioactive beam line. The α core fragments at forward angles were detected in coincidence with the recoiled protons at large angles. From this coincident measurement the valence nucleon knockout mechanism and the core knockout mechanism can be separated according to the polar angle correlation between the core fragments and the recoiled protons. It is demonstrated that, when reconstructing the resonant state of a weakly bound nucleus, the contamination resulting from the core knockout mechanism should be eliminated in order to obtain the correct structure information.     

Isospin dependence of the isotopic distributions from 36Ar and 40Ar fragmentation at about 60 MeV/nucleon

Fragments produced in the reactions of 69 MeV/nucleon ³⁶Ar and 55 MeV/nucleon ⁴⁰Ar on a Be target have been measured experimentally. The isotopic distributions from fragmentation reaction for both projectiles are compared with modified statistical abrasion-ablation model calculations. A strong isospin effect exhibits in the fragment distributions produced in ³⁶Ar and ⁴⁰Ar fragmentation. Experimental evidence for the disappearance of the isospin effect in the isotopic distributions produced by projectile fragmentation is observed with the increase of the violence of nuclear reaction. Received: 15 November 2000 / Accepted: 11 April 2001     

Complete fusion in a light heavy-ion reaction from 2.5 to 20 MeV/nucleon

Mass distributions of evaporation-residue-like fragments have been measured using a time-of-flight system for the reaction ²⁰Ne + ²⁶Mg in the energy range of 51 to 400 MeV bombarding energy for ²⁰Ne. A good mass resolution allowed for the separation of the evaporation residues and fragments from two-body reactions like e.g. damped processes. The residue distributions were compared with evaporation calculations. The analysis of velocity spectra measured at bombarding energies of 85–395 MeV showed incomplete momentum transfer for evaporation-residue-like fragments at higher energies. Statistical-model calculations and Monte Carlo methods applied to the calculation of the velocity spectra have been used to extract the complete-fusion cross section.