Search Results (6 total)

Evaporation residues (ER) of Z=34–42 were measured in coincidence with emitted protons, deuterons, tritons, and α particles for the reaction ⁸⁴Kr+²⁷Al at a ⁸⁴Kr bombarding energy of 1260 MeV. Our study demonstrates the presence of a strong preequilibrium component in the reaction yield. The assumption of a forward center-of-mass angular distribution for the emission of energetic protons and α, following full momentum transfer, gives the best description of the observed experimental data. This description differs substantially from the one provided by prevailing models of incomplete fusion.

The proton-unbound nucleus ¹¹N has been studied via kinematic reconstruction of the emitted proton in coincidence with the residual ¹⁰C daughter nucleus. Resonances in ¹¹N were populated by using a 40 MeV/nucleon radioactive beam of ¹²N to induce the reaction ⁹Be(¹²N,¹¹N), followed by the proton decay of ¹¹N. The decay energy spectrum was constructed from the energies and separation angle of the ¹⁰C and the proton. In addition to protons from the known 1/2^- state, at 2.24 MeV above the proton decay threshold, another peak is seen near 1.45 MeV. This peak could potentially be due to the predicted 1/2⁺ ground state and/or due to the decay of the 3/2^- state to the first excited state of ¹⁰C

The excitation energy of the primary products from the reaction ⁵⁶Fe on ¹⁶⁵Ho at 672 MeV was determined by the kinematic coincidence technique. The fraction of the total excitation energy of the system stored in the projectilelike fragment was found to decrease with increasing energy loss. However, thermal equilibrium is not reached, even at the highest energy damping. A small correlation between excitation energy partition and reaction exit channel was observed. Monte Carlo simulations of the present experiment confirmed that some of this correlation is due to the finite resolution of the measured parameters. © 1996 The American Physical Society.

The charge and mass of the projectile-like fragments produced in the 15-MeV per nucleon ⁴⁰Ca+²⁰⁹Bi reaction were determined for products detected near the grazing angle. Neutron number-charge (N-Z) distributions were generated as a function of the total kinetic energy loss and parametrized by their centroids, variances, and correlation coefficients. Although the initial system is very asymmetric, after the interaction, a drift of the charge and mass centroids toward further asymmetry is observed. The production of projectile-like fragments is consistent with a tendency of the projectile-like fragments to retain the projectile neutron-to-proton ratio 〈N〉/〈Z〉≃1. The correlation coefficient remains well below 1.0 for the entire range of total kinetic energy lost. Predictions of two nucleon exchange models, Randrup’s and Tassan-Got’s, are compared to the experimental results. The models are not able to reproduce the evolution of the experimental distributions, especially the fact that the variances reach a maximum and then decrease as function of the energy loss. This behavior supports the hypothesis that some form of projectile-like fragmentation or cluster emission is perturbing the product distribution from that expected from a damped mechanism.

The charge and mass of the projectilelike fragments produced in the 12-MeV/nucleon ⁵⁶Fe+¹⁶⁵Ho reaction were measured at a laboratory scattering angle of 16°. The mass and charge distributions of the projectilelike fragments were generated as a function of total kinetic energy loss (TKEL), and characterized by their neutron and proton centroids and variances, and correlation factors. A weak drift of the system towards mass asymmetry, opposite to the direction which minimizes the potential energy of the composite system, was observed. The increase in the variances with energy loss is consistent with a nucleon exchange mechanism as a means for energy dissipation. Predictions of two nucleon exchange models, Randrup’s and Tassan-Got’s models, are compared to the experimental results of the 672-MeV ⁵⁶Fe+¹⁶⁵Ho reaction and to other Fe-induced reactions. The proton and neutron centroids were found to be generally better reproduced by Tassan-Got’s model than by Randrup’s model. The variances and correlation factor are well reproduced for asymmetric systems by both models.

Projectilelike fragments were detected and characterized in terms of A, Z, and energy for the reactions ³⁷Cl on ⁴⁰Ca and ²⁰⁹Bi at E=7.3 MeV/nucleon, and ³⁵Cl on ²⁰⁹Bi at E=15 MeV/nucleon, at angles close to the grazing angle. Mass and charge distributions were generated in the N-Z plane as a function of energy loss, and parametrized in terms of their centroids, variances, and coefficients of correlation. The results are compared to the predictions of two current models based on a stochastic nucleon exchange mechanism. The drifts of the charge and mass centroids for the system ³⁷Cl on ⁴⁰Ca are consistent with a process of mass and charge equilibration mediated by nucleon exchange between the two partners, followed by evaporation. The asymmetric systems show a strong drift toward larger asymmetry, with the production of neutron-rich nuclei. It is concluded that this is the result of a net transfer of protons from the light to the heavy partner, and a net flow of neutrons in the opposite direction. Model predictions fail to reproduce in detail the evolution of the centroids for asymmetric systems. The variances for all systems increase with energy loss, as would be expected from a nucleon exchange mechanism. However, the variances for the reaction ³⁷Cl on ⁴⁰Ca are higher than those expected from that mechanism, and the variances for the reaction ³⁵Cl on ²⁰⁹Bi start decreasing after about 100 MeV of energy loss. The coefficients of correlation indicate that the transfer of nucleons between projectile and target is correlated, as expected from Q-value constraints to the valley of β stability.