B. Jakobsson

Promptly emitted particles in nuclear collisions

Abstract We discuss a mechanism in which the nucleons transferred in nuclear collisions are emitted promptly into the continuum via the coupling of internal nucleon motion to the relative motion of the nuclei. The dynamics and the details of transfer are treated in the proximity picture. High energy components of nucleon spectra from fusion experiments are compared to the model predictions.

Light output and energy resolution of CsI, YAG, GSO, BGO and LSO scintillators for light ions

The light output and energy resolution for the scintillators CsI(Tl), YAG(Ce), GSO(Ce), BGO and LSO(Ce) have been measured with 1H, 2H and 3He ions in the energy region ∼ 3–20 MeV/nucleon using photodiodes for the light readout. A very good energy resolution of ∼ 0.62% for 45 MeV 3He-particles has been obtained for CsI. The YAG(Ce), GSO(Ce) and LSO(Ce) crystals are non-hygroscopic, have fast decay time as main component and are well suited for experiments with high counting rates and strict timing requirements. The LSO crystal gives the best energy resolution, but reveals strong quenching for heavy ions. The GSO crystal is a good candidate for operation in UHV environment and has high stopping power, short decay time (56 ns) and moderate quenching.

Elastic and inelastic scattering of 1.03 GeV 12C projectiles

Abstract Elastic scattering cross sections of 86 MeV/N 12C ions on 12C, NATCa, 89Y and 208Pb targets has been measured together with inelastic scattering to the 4.4 MeV state of 12C. There is some indication for giant (quadrupole) resonance excitation in 40Ca. Optical model and DWBA analyses are reported. Nuclear transparency effect is discussed.

Interactions of 2 GeV/Nucleon 16O with Light and Heavy Emulsion Nuclei

Heavy ion interactions in nuclear emulsions induced by 2 GeV/nucleon 16O have been studied. The reaction cross sections determined are 337-85+56 mb, 1007-174+175 mb and 2180-231+304 mb for interactions with H, CNO and AgBr, respectively. Energy-, angular- and transverse momentum distributions of non-relativistic protons (E400 MeV) and all He nuclei have been analysed. Statistical models assuming small correlations among nucleon momenta can account for the main part of the He emission. The energy- and transverse momentum distributions of protons, emitted from light as well as heavy target nuclei indicate that intranuclear nucleon-nucleon scattering is the most important proton emission process. The angular distributions of both high energy protons and high energy He nuclei emitted from the target nucleus differ considerably in central and peripheral 16O-AgBr interactions. In order to explain the angular distributions of high energy protons and He nuclei in events with extremely small impact parameter, non-statistical phenomena, possibly hydrodynamic shock wave emission, must be considered.

On the observation of a transition from fusion to multifragmentation in high multiplicity 16O induced reactions

Abstract We have studied high multiplicity 16 O + Br and 16 O + Ag collisions from 10 A to 220 A MeV on an event-by-event basis. The collisions with the highest multiplicity are fusion-like for energies below 35 A MeV whereas at higher energies the onset of multifragmentation (two or more medium mass fragments) is observed with a charge distribution which gets less and less wide with increasing energy. Correlations between high moments of the charge distribution and the maximum charge or the total multiplicity have been studied. These correlations are generally well described by statistical models. Predicted signals of critical behaviour are however not observed.

Scaling properties of charged particle multiplicity distributions in oxygen induced emulsion interactions at 14.6, 60 and 200 A GeV

Abstract The multiplicity distributions of shower particles (ns) are measured in inclusive inelastic oxygen emulsion interactions. Scaling is observed in the normalized variable ns/〈ns〉 for 14.6, 60 and 200 AGeV. The dependence of 〈ns〉 on the charge flow in the forward direction (QZD) and the distribution of the number of participating projectile protons is examined. The normalized multiplicities as a function of QZD seem also to be independent of incident energies. A comparison with the Lund model Fritiof yields satisfactory agreement.

Projectile fragments from 86 MeV/nucleon 12C induced reactions

Abstract An 86 MeV/nucleon 12 C beam has been used to bombard targets of C, Ag and Au. Energy spectra of reaction products with Z = 3−6 and A = 6−12 have been measured at angles between 3° and 20°. A simple fragmentation model, while predicting approximately the gross features of the data, fails to describe the results in detail.

Mass resolution of recoil fragment detector telescopes for 0.05–0.5 A MeV heavy recoiling fragments

Abstract The factors governing the mass resolution for 0.05–0.5 A MeV recoil nuclei have been investigated for detector telescopes in which carbon-foil time zero detectors and ion-implanted silicon detectors are used to determine the time of flight and energy respectively. Experimentally determined second moments of the mass distribution have been compared with theoretical estimates based on literature data. The experimental mass resolution is in reasonably good absolute agreement with theoretical estimates. For low energy ( A MeV) particles the mass resolution is dominated by the contribution from the silicon detector and thus largely independent of timed flight length. In fact for detection of very low energy (0.1 A MeV) recoil nuclei timed flight lengths of less than 0.22 m are sufficient.

Production of charged pions in intermediate-energy heavy-ion collisions

Abstract Cross sections for the production of π + and π − have been measured over a wide range of angles for 12 C + 7 Li, 12 C + 12 C and 12 C + 208 Pb collisions at 60 A , 75 A and 85 A MeV. Energy distributions are less steep and absolute yields of pions larger than expected from a straightforward Fermi gas nucleon-nucleon scattering prescription. The apparent velocity of the system in which the π + emission is symmetric, is closer to the nucleus-nucleus c.m. velocity than to the mean speed system. The Coulomb-corrected π − π + ratio is close to unity for 12 C + 12 C. The corresponding ratio for 12 C + 208 Pb is, however, much larger than expected from the neutron excess in 208 Pb only.

The disintegration of nuclei in violent heavy ion interactions at 55A MeV-110A MeV

High multiplicity12C induced reactions in Ag(Br) at energies between 55A MeV and 110A MeV have been selected and investigated event by event in nuclear emulsions. Only a fraction of these events can possibly be described in terms of a normal thermal spectator-participant mechanism. Several events exhibit a violent breakup into several light and medium-mass fragments.A strong suppression of projectile associated proton- and composite particle emission in the forward direction is found in comparison with inclusive spectra. A large part of the low energy protons originates from a very slow source, with a velocity comparable to that of the heaviest fragment. The parallel fraction of the c.m. energy in each event, which is governed by the more energetic protons, has a broad distribution with a mean value of 0.61 and thus shows no signals of collective production mechanisms.