B. Norén

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.

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.

Two-neutron interferometry measurements

Abstract The results of analysis of two-neutron correlations in the region of small relative velocities are presented. The influence of spurious correlations on the form of correlation function is considered in detail. Data analysis and computer simulations were performed for a specific detector configuration with close angular position and different distances between the target and detector modules. The features of different methods of cross-talk elimination are examined. The proposed method is verified and the first results of cross-talk free correlation functions are presented for the ArAu reaction at 60 MeV u measured with the DEMON detector at GANIL.

Simultaneous neutron-neutron proton-neutron and proton-proton interferometry measurements

Abstract This paper describes a technique to perform simultaneous neutron-neutron, proton-neutron and proton-proton nuclear interferometry measurements. Experimental arrangements for intermediate energy heavy ion interferometry experiments are presented and their limitations are investigated. The construction of correlation functions, particularly with respect to normalization and background corrections is discussed. Some new results on correlation functions from the reaction 30 A MeV 40 Ar+ 12 C are shown and possibilities to improve the interferometry technique are discussed.

Charged pion production and projectile breakup cIN 85A MeV 12C-induced heavy-ion reactions

Abstract Charged pions have been measured at 70° in coincidence with projectile-like fragments in 12 C + 12 C, 12 C + 116 Sn and 12 C + 124 Sn reactions at 85A MeV. Neither the π + emission nor the π − /π + ratio exhibit differences for 124 Sn and 116 Sn targets outside those expected from the isospin difference. Inconsistencies in the target mass dependence of the pion yield disappear if a correction for reabsorption is included. After this correction, we observe a strong, ~ A 1.1 , mass dependence. The projectile breakup is significantly stronger for pion-producing collisions than for the average collision indicating a much stronger abundance of central collisions.

Neutron-proton interferometry in 30A MeV40Ar+197Au collisions

Abstract Neutron-proton correlation functions in 30A MeV 40 Ar + 197 Au , 12 C , CH 2 reactions have been measured. In contrast to the nn and pp correlations, which exhibit the shape expected from quantum symmetrization effects and nuclear+Coulomb (pp) final-state interaction, the np function shows much less correlation strength. This may be due to Coulomb repulsion on the proton and/or to a larger effective spin than expected. Selecting high energy nucleons strengthens both the np and pp correlations.

Maximum breakup of symmetric and asymmetric heavy ion reactions between 5A and 2100A MeV

The maximum breakup of 16O + 107Ag and 84Kr + 107Ag collisions at energies from 5A to 2100A MeV has been investigated. Comparisons between data and calculations within a fusion + evaporation model at low energies and fusion + hadrochemical fireball decay model at higher energies show that phenomena like pre-equilibrium emission, compression and collective flow must be considered. At (34 ± 2)A MeV we observe the cease of the compound evaporation process and the onset of multifragmentation for the highest multiplicity 16O + 107Ag collisions.

A compact range telescope for K+ measurements

Abstract We present range telescopes for measurements of low energy K + mesons together with first in-beam results. The hardware trigger, based on the observation of the μ + from the K + → μ + + ν μ decay channel, is designed for subthreshold hadron-nucleus and heavy ion reactions, where the kaon fraction of the total number of charged particles is ⪡ 10 −4 . The geometrical efficiency is ∼15% and the total efficiency ∼4% for K + registration in the present version of the detector.

Experimental isotopic effects in comparison to statistical prescriptions for fragment production in 32A MeV and 14A MeV 14N + 112,124Sn reactions

Results on isotopic effects in the production of light fragments in reactions of 14A and 32A MeV 14N ions with 112Sn and 124Sn are presented. The data are discussed in the frameworks of classical Weisskopf evaporation and an alternative Fermi gas prescription. The source isospin dependence of the production rates is consistent only with the latter prescription. It is emphasized that similar data from p-nucleus reactions and from projectile-like fragments in 40Ar induced reactions behave in the same way.