Nuclear Orbiting At Low Energy Nuclear Collisions

Physics Letters B, 1989

The cross sections for the multiple breakup of 160, a4N and ~zC projectiles scattered by a Au target were measured with an array of 34 detectors. The excitation spectrum of the primary projectile-like nucleus was reconstructed from the measured positions and kinetic energies of the individual fragments. Calculations of the yields based on a sequence of binary decays are presented. The study of the breakup of a projectile into its component fragments generally has been based either on the inclusive detection of a single fragment or on two-particle coincidence measurements [ 1 ]. These types of experiments can reveal much about the breakup process when the two-body exit channels are dominant [2,3]. However, when a larger number of projectile fragments is produced in a nuclear reaction, exclusive measurements are necessary to determine the extent of multiple dissociation. Such information is important in understanding the dynamics responsible for projectile excitation in a peripheral collision, and for addressing the question of prompt versus sequential decay [4-6]. In this Letter we report exclusive measurements of the breakup of light projectiles into as many as five charged particles. Because we are able to detect beam velocity fragments with high efficiency, it is possible, under the assump

… Journal of Modern …, 2010

The mixing of the quasifission component to the fissionlike cross section causes ambiguity in the quantitative estimation of the complete fusion cross section from the observed angular and mass distributions of the binary products. We show that the partial cross section of quasifission component of binary fragments covers the whole range of the angular momentum values leading to capture. The calculated angular momentum distributions for the compound nucleus and dinuclear system going to quasifission may overlap: competition between complete fusion and quasifission takes place at all values of initial orbital angular momentum. Quasifission components formed at large angular momentum of the dinuclear system can show isotropic angular distribution and their mass distribution can be in mass symmetric region similar to the characteristics of fusionfission components. As result the unintentional inclusion of the quasifission contribution into the fusion-fission fragment yields can lead to overestimation of the probability of the compound nucleus formation.

Nuclear Physics A, 1984

After a review of the various theoretical models which describe the fast nucleon emission in heavy-ion reactions at bombarding energies lower than 100 MeV/u, the Boltzmann equation is discussed as a tool for studying the reaction mechanisms in this energy range. The Boltzmann equation allows to analyze the balance between one-and two-body processes. A linearized version is derived to study the transport in nuclei of fast nucleon flows generated by the reaction dynamics. Results are presented showing that the high energy tails of the spectras can be interpreted without reference to statistical emissions from hot nuclear fragments. 1. INTRODUCTION Free nucleons are a quasi-permanent output of the heavy-ion collisions ; the least bound nucleons in nuclei have a binding energy of approximately 8 MeV, which is small when compared with the relative kinetic energy of the ions. Even at low energies, nucleon emission is then an open channel for the dissipation of the excitation energy, the linear and angular momenta of the interacting system. At very low bombarding energies (a few MeV per nucleon), it is generally accepted that the nucleon emission occurs statistically from either the emerging fragments or from the compound system (see refs. 1-4). At higher bombarding energies (typically higher than 8 MeV per incident nucleon), there are well established evidences for non-statistical neutron5-8 and proton'-I1 emissions. Due to their non-equilibrated character, these emissions have been thought to bear signatures of the processes from which they originate and, by the way, to provide probes of the reaction dynamics. This work will follow such a philosophy ; it will be specialized in reactions the bombarding energies of which do not exceed 100 MeV per nucleon. This energy range is presently under focus owing to the recent availability of experimental data12 ; it is interesting too from a theoretical point of view, since one expects to observe the transition between a regime where the reactions are mainly governed by the nuclear mean field and a regime where, the binding energies the nucleons becoming progressively negligible, the reactions are dominated the individual collisions.

Physics Letters B, 1987

Les corrélations angulaires entre fragments de fission pour le systëme a8 Ni + 232 Th à 20, 25 et 30 MeV/u montrent une persistance de la bosse correspondant aux grands transferts qui suggère que sa disparition pour le système 40 Ar + 232 Th à 44 MeV/u n'est pas due à une limitation en énergie d'excitation et que la taille et la vitesse du projectile ont aussi un rôle important. De grandes vitesses relatives sont observées pour les fragments de fission pour les grands transferts (~ 9,5 GeV/c) qui pourraient provenir d'un mécanisme de fission plus exotique des noyaux chauds.

Results from the asymmetric reactions 80 and 100 MeV/u La+ Care presented and compared to earlier work with the same system at 18 and 50 MeV/u. Fragment-fragment correlations, cross sections, and distributions in velocity space indicate the continued dominance of a quasi-binary decay mechanism with increased emission of light charged particles. The distributions in velocity also indicate a progression toward a "fireball" type of reaction mechanism. However, the angular distributions of the emitted fragments are incompatible with statistical production mechanisms that have successfully explained the lower energy results, and indicate the dynamical nature of the emission process. Dalitz plots of triple complex fragment coincidences are presented in order to investigate the nature of the multibody decays.

Nuclear Physics A, 1995

A 4~r mulfidetector array with a high efficiency has been used to detect the charged products from reactions induced by 36At on 2~kl at energies ranging from 55 to 95 MeV/u. Well-characterized events were selected and sorted as a function of the impact parameter. Fusion or full stopping events have a very small cross section. Dissipative binary collisions accompanied by pre-equilibrium (mid-rapidity) emission, and followed by de-excitation of the quasi-projectile and quasi-target, were found to dominate for all impact parameters. The mass of the quasi-projectile has been reconstructed from its products and found to be slightly below the projectile mass. Isotropic emission in its rest frame has been observed at all energies and impact parameters, indicating that equilibrated nuclei may have been formed. The excitation energy of the quasi-pro

Physical Review C, 2015

The dynamics of the reactions forming compound nuclei using loosely bound projectiles is analysed within the framework of dynamical cluster decay model (DCM) of Gupta and Collaborators. We have analysed different reactions with 7 Li, 9 Be and 7 Be as neutron rich and neutron deficient projectiles, respectively, on different targets at the three E lab values, forming compound nuclei within the mass region A∼ 30 − 200. The contributions of light particles LPs (A ≤ 4) cross sections σLP , energetically favoured intermediate mass fragments IMFs (5 ≤ A2 ≤ 20) cross sections σIMF as well as fusion-fission ff cross sections σ f f constitute the σ f us (=σLP +σIMF +σ f f) for these reactions. The contribution of the emitted LPs, IMFs and ff fragments is added for all the angular momentum upto the ℓmax value, for the resepctive reactions. Interestingly, we find that the ∆R emp , the only parameter of model and uniquely fixed to address the σ f us for all other reactions having same loosely bound projectile at the chosen incident energy. It may be noted that the dynamical collective mass motion of preformed LPs, IMFs and ff fragments or clusters through the modified interaction potential barrier are treated on parallel footing. We see that the values of modified interaction barrier heights ∆V emp B for such reactions are almost of the same amount specifically at the respective ℓmax values.

Nuclear Physics A, 1987

Recent experimental results on two-particle correlations measured in intermediate energy nucleus-nucleus collisions are reviewed. The emission and the sequential decay of particle unstable nuclei turn out to be an essential mechanism of the disintegration of nuclear systems. Consequences for single particle observables are discussed. In several experiments emission temperatures of about 5 MeV are found for sLi nuclei. These surprising observations are compared to fragment temperatures calculated with a statistical multifragmentation model. During the non-equilibrium initial stage of a nuclear reaction the individual degrees

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 1988

We report some results obtained during the study of the interaction of 960 MeV/nucleon 238U, 460 MeV/nucleon 238U, and 460 MeV/nucleon 139La ions with light target atoms. CR-39 ( a polycarbonate, having a composion of C12 , HI8 , 07 ) was used as the target as well as the detector. Experimental values of charge changing mean free path have been obtained and compared with those computed using geometrical overlap model. projectiles in the CR-39 plastic have also been measured. Binary fission is found to be the most common mode of interaction. However, some higher order fission events along with events having exceptionally high multiplicity (clusters, containing more than thirty small tracks) have also been observed for 960 MeV/nucleon 238U-ions near their Bragg peaks. The origin of these high multiplicity events could not be traced to a single isotopic source, such as the presence of a tiny speck of radioactive contamination.

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.