L. Beaulieu

Fission transient times from fission probabilities of neighboring isotopes

Abstract We present a new and straightforward method to estimate the fission transient time by utilizing the cumulative fission probabilities of neighboring isotopes. The fission probabilities were determined as the ratio of the measured fission cross sections to the Bass Model fusion cross sections. For five neighboring 185–189 Os compound nuclei produced in 3 He/ 4 He-induced reactions on separated isotope W targets, the transient time τ D is estimated to be −21 seconds for excitation energies less than 150xa0MeV, and the most likely value of τ D is ≈10×10 −21 seconds.

Statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy

Multifragment emission following {sup 129}Xe+{sup 197}Au collisions at 30A, 40A, 50A, and 60A MeV has been studied with multidetector systems covering nearly 4{pi} in solid angle. The correlations of both the intermediate mass fragment and light charged particle multiplicities with the transverse energy are explored. A comparison is made with results from a similar system {sup 136}Xe+{sup 209}Bi at 28A MeV. The experimental trends are compared to statistical model predictions. {copyright} {ital 1999} {ital The American Physical Society}

Statistical exploration of fragmentation phase space and source sizes in nuclear multifragmentation

Abstract The multiplicity distributions for individual fragment Z values in nuclear multifragmentation are characterized by their maximum value m Z . A strong indication of statistical coverage of fragmentation phase space is inferred from the dependence m Z = Z 0 / Z , where Z 0 is the source size. The source sizes coincide with those extracted from the analysis of fixed multiplicity charge distributions.

Precise shell effects and barriers from fission probabilities of neighboring isotopes

Fission excitation functions have been measured and analyzed for a chain of neighboring compound nuclei, from 207Po to 212Po. We present a new analysis which provides an accurate description of the fission barriers and ground state shell effects. Estimates of the fusion cross section are also obtained. The improved accuracy achieved in this analysis may lead to a future detailed exploration of the saddle mass surface.

Exploring alternative (p, n) and (d, n) reactions for BNCT

We report on the yields and energy spectra of neutrons emitted in several deuteron-induced reactions at low energy. The main features of these reactions are presented and discussed with regards to their potential use as sources of epithermal neutron beams for Boron Neutron Capture Therapy (BNCT). Among the studied reactions, the 13C(d,n)14N presents features potentially interesting for a compact accelerator-based neutron source for BNCT.

The Role of Statistics and Thermodynamics in Nuclear Multifragmentation

The natural limit of binomial reducibility in nuclear multifragmentation is observed in excitation functions for intermediate mass fragments (IMF) of a given element Z. The multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots constructed from the average multiplicity of each element. Emission barriers are extracted from the slopes of the Arrhenius plots and their possible origin is discussed.

Interpreting multiplicity-gated fragment distributions from heavy-ion collisions

In recent years, multifragmentation of nuclear systems has been extensively studied, and many efforts have been made to clarify the underlying physics. However, no clear consensus exists on the mechanism for multifragmentation. Is the emission of intermediate mass fragments (IMF: 3 {le} Z {le} 20) a dynamical process (brought on by the occurrence of instabilities of one form or another) or a statistical process (i.e. the decay probabilities are proportional to a suitably defined exit channel phase space)? Historically the charge (mass) distribution has played and still plays a very important role in characterizing multifragmentation. Since this subject`s inception, the near power-law shape of the charge and mass distributions was considered an indication of criticality for the hot nuclear fluid produced in light ion and heavy ion collisions. Here, the authors have studied different aspects of the charge distributions. The implications of the experimental evidence presented here are potentially far reaching. On the one hand, the thermal features observed in the n-fragment emission probabilities for the {sup 36}Ar + {sup 197}Au reaction extend consistently to the charge distributions and strengthen the hypothesis of the important role of phase space in describing multifragmentation. On the other hand, they have investigated charge correlation functions of multi-fragment decays to search for the enhanced production of nearly equal-sized fragments predicted in several theoretical works.