Correlations between projectilelike and targetlike fragments in the reaction+2744-MeV/nucleon

Abstract

Correlations between projectilelike and targetlike fragments have been measured in the reaction 27 Al + 44-MeV/nucleon 40 Ar. These correlations can be consistently interpreted in the framework of an abrasion model including dissipation. However, they can also be described by a binary process in which, before decaying sequentially by particle emission, projectile and target share an approximately equal amount of excitation energy with no significant mass transfer.PACS numbers: 25.70.Np For projectiles of intermediate energies (20 to 100 MeV/nucleon), peripheral collisions between heavy ions have recently been subjected to extensive studies, 1 " 4 motivated by a possible rapid change 5 in the reaction mechanism as the projectile velocity becomes comparable to the velocity of the nucleons inside the nucleus. Such a transition is suggested by a rapid broadening of the projectilelike-fragment (PLF) momentum distributions 6 between 20-and 40-MeV/nucleon projectile energy. This increase in momentum width is expected in a transition from transfer to abrasion, due to the opening of the phase space made available to the nucleons removed from the projectile. 7,8 Very schematically, for projectile energies smaller than --20 MeV/nucleon, most of these fragments are considered as the remnants of an incomplete fusion process in which only part of the projectile fuses with the target, 9 wheres for energies greater than 200 MeV/nucleon, they are thought to be produced by a fast removal (abrasion) of the nucleons in the region of overlap between projectile and target. 10 Thus, it would be interesting to determine over which energy range the transition between those two processes occurs. However, the other PLF properties (angular distributions, isotopic ratios, energy damping) evolve smoothly from the low-energy regime to relativistic energies, showing hardly any evidence of a change in the reaction process. Thus, PLF properties alone do not appear as a sensitive probe of the reaction mechanism. A better signature could be the amount of linear momentum imparted to the target since in the hypothesis of massive transfer, the nucleons removed from the projectile are captured by the target to which they communicate their linear momentum, whereas in the case of abrasion, only a small fraction of this momentum is imparted to the target through friction forces. Thus, the onset of abrasion should manifest itself by a sharp drop in the linear momentum imparted to the targetlike fragments (TLF's).To better determine the underlying reaction mechanism in the expected transition energy region, we have measured the mass, angular, and velocity correlations between PLF's and TLF's in the reactions induced by 1760-MeV 40 Ar on 27 A1, for which there already exist extensive inclusive data on PLF's. {x The experiment was performed using a 44-MeV/ nucleon 40 Ar beam at the Grand Accelerateur National d'lons Lourds facility. In order to reduce energy and angular straggling of the TLF's the self-supported 27 A1 target was only 100 jug/cm 2 thick. ...

The ablation stage in the fast abrasion model

“…6 where the A/Z ratio of the primary fragments, which was assumed to be equal to the A/Z ratio of the projectile, is indicated by the dashed line. As shown in [8], this correlation is well reproduced by a fast abrasion model. For masses ./I~F below 30, the agreement between the calculation and the data is excellent.…”

“…Some indication has been obtained through various experiments, that may give indirect estimates [4][5][6][7][8]. Some indication has been obtained through various experiments, that may give indirect estimates [4][5][6][7][8].…”

Properties of projectile-fragments in the 40Ar+27Al reaction at 44 A MeV. Comparison with a multisequential decay model

“…For the same reaction, it has been shown previously [3] that PLF-TLF coincidence data could be interpreted as the result of a two-step process: a binary collision between the projectile and the target with a very small net exchange of nucleons leading to primary excited projectile and target nuclei which then decay by particle emission. Within this hypothesis, it was shown that the projectile and target primary fragments share an amount of excitation energy which evolves from equal sharing for peripheral collisions to sharing in the mass ratio (equal temperature) for more central collisions.…”

“…They de-excite by emission of light particles and/or fragments with velocity close to those of the projectile and of the target respectively. Later, a coincidence experiment [3] between projectile-like and target-like (TLF) fragments using the same reaction ( 40 Ar+ 27 Al reaction at 44 A.MeV) showed a strong correlation between PLFs in the forward direction and TLFs detected in a wide angular range up to 90 • . Both a three-body abrasion-ablation mechanism (low excitation energy in the primary PLFs and TLFs) or a simple two-body mechanism like the so-called "deep inelastic" collisions (high excitation energy in the primary projectile and target nuclei) were able to account rather well for the experimental results.…”

Correlation functions of light charged particles from projectile-like fragment source in and 77 MeV 40Ar + 27Al collisions

“…In particular, this is true for the reverse kinematics reaction Ar + Al, investigated by several authors [8][9][10][11][12][13][14][15][16][17][18]. In this paper, we aim to study light charged particle (LCP) emission from the PLF, in E/A = 44 and 77 MeV 40 Ar + 27 Al collisions.…”