L. Heilbronn

Fragment production in 14N+C, Ni, Ho reactions at 35 MeV/nucleon

Abstract Inclusive fragment production from the collisions of 35 MeV/Nucleon 14 N with carbon, nickel, and holmium targets has been measured in the angular range of 7–23°. The energy spectra of many of the isotopes of Li, Be, B, C and N were determined. In an energy/nucleon representation the spectra at a given angle are similar for all fragments and all targets. The spectra contain contributions mainly from two components, quasielastic and deep inelastic, whose development can be followed as the fragment angle changes. The quasielastic structure, a broad peak, is most pronounced at high fragment energies and at the smaller angles. The deep-inelastic component falls off with fragment energy and becomes dominant at the large angles. The spectra for fragments with 6 ⩽ A ⩽ 12 were decomposed into these two components. The shape of the quasielastic component is consistent with a two-step model in which an early fragmentation is followed by a subsequent mass pick-up from the participant zone. The maxima and the average energies of the quasielastic distributions and the logarithm of the energy integrated quasielastic yields for the different light isotopes depend approximately linearly on angle for all three targets. The relative isotope yields indicate a slight dependence on the neutron/proton ratio of the target for the quasielastic component and a more pronounced one for the deep-inelastic component.

Excitation of discrete particle-unbound states in heavy-ion collisions

Abstract Neutron spectra in coincidence with fragments have been observed in 14 N- 165 Ho collisions at 490 MeV. Contributions to the spectra from excited light fragments are very pronounced when the fragments detector and the neutron detector are in colinear geomwtry. Relative velocity spectra then reveal that neutron decay of a single, well-known excited state dominates. In inclusive spectra of neutrons or protons these effects are still present and may not be disregarded.

Temperatures determined from neutron emission in nucleus-nucleus collisions

Abstract Most neutron spectra from 14N+165Ho collisions at 35 MeV/nucleon are described by two moving thermal sources, one at a temperature of ≈2.5 MeV and the other of ≈8 MeV. Resonances in gragment-neutron relative velocity spectra are used to determine a temperature from the relative populations of excited states of 13C nuclei. There is a discrepancy with the equilibrium assumption in that the fitted value, ≈1 MeV, does not match that of either thermal source.

Analysis of projectile fragmentation in intermediate-energy heavy-ion collisions

Abstract An analytical form is given for the entire energy range of quasielastic fragment spectra produced in intermediate-energy heavy-ion collisions. The fit parameters are related to physical quantities such as the probability of direct fragmentation versus damped fragmentation and the momentum width of the direct fragmentation peak. The formulation is applied to fragment spectra at 10° from the 14N+165Ho reaction at E/A = 35 MeV. It is suggested that Coulomb deflection and impact-parameter selection have a decisive effect on fragment spectra produced in peripheral collisions. The smaller the Z/A of the detected fragment at a given angle, the smaller the impact parameter of the reaction.

Production rates of excited fragment isotopes from the36Ar+Ag reaction at 35 MeV/nucleon

Previous studies showed that the binding energy plays a systematic and important role in the production of ground-state fragments in intermediate energy, heavy ion reactions. The production rates were measured as a function of fragment kinetic energy at angles of 15°, 30°, 45° and 60° for excited fragments of7Li,8Li,11Be and12B. Using a thermal model the total production of neutron unbound excited states was determined, and it was found that their production rates correspond to the previous systematic behaviour using the binding energies corrected by the excitation energies.