Search Results (4 total)

Invariant transverse-velocity spectra of intermediate-mass fragments were measured with the 4π multidetector system INDRA for collisions of ¹⁹⁷Au on ¹⁹⁷Au at incident energies between 40 and 150 MeV per nucleon. Their scaling properties as a function of incident energy and atomic number Z are used to distinguish and characterize the emissions in (i) peripheral collisions at the projectile and target rapidities, and in (ii) central and (iii) peripheral collisions near midrapidity. The importance of dynamical effects is evident in all three cases and their origin is discussed.

Results of fission fragment mass-energy distributions of the compound ²²⁶Th nucleus formed in the sub-barrier fusion reaction ¹⁸O+²⁰⁸Pb at an energy of ¹⁸O ions E_lab=78 MeV are reported. The reaction has been studied twice using two different accelerators, and both sets of experimental data agree quite well. Performed analysis of the experimental data with the use of a new multicomponent method has shown that alongside the well-known modes, i.e., the symmetric (S) and two asymmetric modes standard-one and standard-two, a high-energy mode standard-three has manifested itself. The last named mode appears due to the influence of the close-to-sphere neutron shell with N≈50 in the light fission fragment group. Theoretical calculations of the prescission shapes of the fissioning nuclei ^224,226Th confirm this conclusion.

Isotopically resolved intermediate-mass fragments and light charged particles have been detected from the reactions ⁴⁰Ar and ⁴⁰Ca with ⁵⁸Fe and ⁵⁸Ni at E_beam=33 and 45 MeV/nucleon. There is an angular dependence to the isotopic ratios. A moving source analysis shows that fragments emitted at Θ_lab=40° can be attributed primarily to a composite source while the fragments emitted at backward angles are primarily from a targetlike source. The results are compared to predictions of QMD, BUU, and GEMINI. QMD generally reproduces the charge distribution and energy spectra and has partial success with the isobaric ratios when the system is chemically equilibrated. All of the models have difficulty reproducing the isotopic ratios when the system is not chemically equilibrated.

We modify the method of Albergo et al. for determining the temperature of an excited nucleus from double ratios of isotope yields and present a statistical model which accounts for the population and decay of excited states of the emitted fragments. Nuclear temperatures are extracted using experimental ratios of isotopic yields of fragments from helium through carbon for the reactions ⁴⁰Ca + ⁵⁸Ni, ⁴⁰Ar + ⁵⁸Ni, ⁴⁰Ca + ⁵⁸Fe, and ⁴⁰Ar + ⁵⁸Fe at 33 MeV/nucleon projectile energy. Using the model we obtain consistent values for the temperature from various isotope combinations within the experimental error when accounting for the population and decay of the excited fragments.