Excitation energy evolution and multi-particle correlations in heavy ion peripheral collisions at intermediate energies (original) (raw)
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On the projectile fragmentation in heavy-ion reactions at intermediate energies
Nucl. Phys. A 466 139, 1987
The two-body fragmentation of the projectile in the target field is described within a three-body dynamic model. Four types of reaction emerge: fusion at low energies and low impact parameters b, elastic and inelastic reactions at high b and two types of fragmentation in peripheral collisions. For high b the two projectile parts are emitted while for low 6 one fragment fuses with the target and only the other one can be detected. In the first case the part which has grazed the target has been strongly slackened and has a velocity of 0.7 V beam for small emission angles to 0.5 V beam for large angles. It might be a contribution to the relaxed fragment events detected at intermediate angles. In agreement with experimental data, the b2 window for this kind of fragmentation is very narrow for heavy quasi-projectiles and widens with decreasing masses. This model allows to reproduce semi-quantitatively the mass distribution of the quasi-projectiles, the position of the maximum in the one-and two-peak energy spectra and the relative importance of the two types of fragmentation.
Target proximity effect and dynamical projectile breakup at intermediate energies
Nuclear Physics A, 2004
Projectile binary breakup has been investigated in 58 Ni + 12 C, 24 Mg, 197 Au at 34.5 MeV/A and 58 Ni + 70 Zn at 40 MeV/A. The fragment angular distributions exhibit an anisotropic pattern showing that breakup is aligned with the direction of scattered quasi-projectile (QP). The correlation functions of the two heaviest fragments have been studied as a function of charge asymmetry. They suggest that the QP decays while still in close proximity of the target. The correlation between the charge and velocity of the two heavy fragments shows that the binary breakup of the QP might originate from an important deformation of the projectile by the target, and that the lighter of the colliding partners also contributes to the aligned emission pattern. E = 40 MeV/nucleon; measured fragments angular distributions, charge and velocity distributions, correlation functions; deduced quasi-projectile breakup mechanism, related features.
Exclusive multidetection and study of projectile breakup at 25 and 35A MeV in
Nuclear Physics A, 1996
The breakup of the projectile 24Mg, excited in peripheral collisions on a gold target, has been investigated at 25 and 35A MeV with a large scintillation-detector array allowing exclusive measurements. Absolute breakup cross sections were deduced and the projectile-like nucleus velocity and excitation energy have been reconstructed. The excitation energy partition between the projectile and the target is found to lay between the limits of equal excitation energy sharing and equal temperature with some evolution from one limit to the other. The statistical nature of the decay mechanism is inferred from global variables. Small-relative-angle analysis is applied to the six-alpha exit channel and the corresponding data were found to be consistent with a sequential evaporation decay mechanism, with some contribution from sequential fission at higher excitation energies. The time scale involved in the breakup of 24Mg projectiles into the 6a and the 5aHH channels has been investigated by examining distortions in the fragment velocity distributions due to the Coulomb field of the target. A decrease in the quasi-projectile lifetime is observed as the mean excitation energy increases from 3.4 to 4.5A MeV. PACS: 25.70-z; 25.70Lm Keywords: NUCLEAR REACTIONS 197Au(24Mg,X); Elab = 25A MeV; Ebb = 35A MeV; Measured multiple projectile breakup; Reconstructed excitation energy; Deduced time scale; Model calculations 0375-9474/96/$15.00
Reaction mechanisms in 3He projectile breakup at 52MeV on 12C, 28Si and 58Ni
Nuclear Physics A, 1984
Inclusive proton and deuteron spectra from 'He-induced reactions on "C, '?ji and '"Ni have been studied. Each spectrum contains a continuum part that may be separated into a broad bump, centred around beam velocity energies at forward angles, and an exponential tail. The properties of each of these components have been investigated as function of outgoing particle, detection angle and target mass. The centroid position of the bump and the bump width are found 10 be almost independent of target mass and detection angle. The total (energy-and angle-integrated) cross sections for the bump show a mass dependence almost proportional to A"' for both protons and deuterons. The total cross section for the exponential tail has a different mass dependence for protons and deuterons:
Bimodal Behavior of the Heaviest Fragment Distribution in Projectile Fragmentation
Physical Review Letters, 2009
The charge distribution of the heaviest fragment detected in the decay of quasi-projectiles produced in intermediate energy heavy-ion collisions has been observed to be bimodal. This feature is expected as a generic signal of phase transition in non-extensive systems. In this paper we present new analyses of experimental data from Au on Au collisions at 60, 80 and 100 MeV/nucleon showing that bimodality is largely independent of the data selection procedure, and of entrance channel effects. An estimate of the latent heat of the transition is extracted. PACS numbers: 05.70.Fh Phase transitions: general studies ; 25.70.-z Low and intermediate energy heavyion reactions ; 25.70.Pq Multifragment emission and correlations
Physical Review C, 1990
We have measured the target fragment production cross sections and angular distributions for the interaction of 16 MeV /nucleon 32 S, 32 MeV /nucleon 40 Ar and 44 MeV /nucleon 40 Ar with 197 Au. We have deduced the fragment isobaric yield distributions and moving frame angular distributions from these data. The fission cross sections decrease with increasing projectile energy and the heavy residue cross sections (which are much larger than previous counter measurements) increase. There is an 1 unusual change in the fragment isobaric yield distributions in the reactions induced by 32 MeV /N 40 Ar and 44 MeV /N 40 Ar. We have used the symmetry properties of the moving frame distributions to show the relative time scale of the reaction mechanisms involved. The fission fragments associated with the peripheral collision peak in the folding angle distribution originate in a normal, slow fission process in which statistical equillbrium has been established. At the two lowest projectile energies, the fission fragments associated with the central collision peak in the folding angle distribution originate in part in fast, non-equilibrium processes. At the highest projectile energies, there are no fission fragments associ"ated with high momentum transfer events. The intermediate mass fragments originate primarily in events in which statistical equilibrium has not been established.
Relaxed and quasi-projectile fragments in heavy-ion reactions
J. Phys. G 17 (1991) 1415, 1991
Analyses of experimental data point out the existence of two well separated velocity spectra for collisions of heavy ions at intermediate impact parameters, In particular the "Ar + I9'Au(35 MeV U-') and 'Ar + '"Ag(60 MeV U-') reactions are investigated. Within the hypthesis of a two-body fragmentation of the projectile in the target field, a three-body dynamic model is used. It allows us to associate the low velocity peak with the projectile part which has grazed the target and has been slowed down by the target field while the high velocity fragment corresponds to the outer remainder part which escapes almost freely. This model quantitatively reproduces the mean position of the energy spectra, the transferred linear momentum and the multiplicity of the detected light particles.
Physical Review C, 2003
Projectile-like fragments (PLF:15≤Z≤46) formed in peripheral and mid-peripheral collisions of 114 Cd projectiles with 92 Mo nuclei at E/A=50 MeV have been detected at very forward angles, 2.1 • ≤θ lab ≤4.2 • . Calorimetric analysis of the charged particles observed in coincidence with the PLF reveals that the excitation of the primary PLF is strongly related to its velocity damping. Furthermore, for a given VP LF * , its excitation is not related to its size, ZP LF * . For the largest velocity damping, the excitation energy attained is large, approximately commensurate with a system at the limiting temperature. PACS numbers: PACS number(s): 25.70.Mn
Breakup of highly excited 35 Cl projectiles on a gold target at 30 A MeV: An exclusive analysis
Projectile excitation and breakup have been studied in the reaction 35C1 + 197Au at 30A MeV. Differential cross sections and energy distributions were measured. The absolute cross sections of 98 different exit channels made of as many as 7 coincident charged fragments have been determined. Such exclusive measurements allow event-by-event reconstruction of the excited primary nuclei. By selecting specific exit channels, we studied the decay of hot nuclei over a wide range of excitation energy. The behaviour of the excited nuclei is consistent with a statistical description. The fragmentation mechanism was also investigated. Although the lowest excited channels are well reproduced by a standard sequential-binary-decay model, evidence is observed for an evolution with excitation energy of the time scale for particle emission. Model calculations have been performed which show that the lifetime of the excited chlorine projectile should decrease by a factor of 4 when the excitation energy increases from 2.3A to 4.3A MeV.