M.A. McMahan

Bio: M.A. McMahan is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Nuclear reaction & Nuclear fusion. The author has an hindex of 7, co-authored 9 publications receiving 577 citations.

Compound-Nucleus Decay along the Mass-Asymmetry Coordinate and the Role of the Businaro-Gallone Point

Abstract: Fragments with atomic numbers covering the entire range of the mass-asymmetry coordinate ($Z=1$ to $Z=\frac{{Z}_{\mathrm{CN}}}{2}$) were observed from the decay of compound nuclei (CN) produced in reactions of 74- and 84-MeV/nucleon $^{74}\mathrm{Ge}$, $^{93}\mathrm{Nb}$, and $^{139}\mathrm{La}$ with $^{9}\mathrm{Be}$ and $^{12}\mathrm{C}$ The evolution of the charge distribution with increasing mass of the compound nucleus ($A=83 \mathrm{to} 151$) reflects the topological change in the potential-energy surface associated with crossing the Businaro-Gallone point

Characterization of hot compound nuclei from binary decay into complex fragments.

Abstract: The emission of complex particles at intermediate energies has been characterized through the reverse-kinematics reactions 25- and 30-MeV/u $^{93}\mathrm{Nb}$ + $^{9}\mathrm{Be}$, $^{27}\mathrm{Al}$. Complex particles observed in binary decays from very hot incomplete-fusion intermediates are shown to originate from compound-nucleus decay, by means of kinetic energies, angular distributions, and absolute yields. The process of complex-particle emission provides a method, applicable throughout the Periodic Table, for studying compound nuclei with temperatures and excitation energies near the expected limit of their existence.

Probing the nuclear liquid-gas phase transition.

Abstract: Fragment distributions resulting from $\mathrm{Au}+\mathrm{Au}$ collisions at an incident energy of $E/A\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}600\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$ are studied. From the measured fragment and neutron distributions the mass and the excitation energy of the decaying prefragments were determined. A temperature scale was derived from observed yield ratios of He and Li isotopes. The relation between this isotope temperature and the excitation energy of the system exhibits a behavior which is expected for a phase transition. The nuclear vapor regime takes over at an excitation energy of 10 MeV per nucleon, a temperature of 5 MeV, and may be characterized by a density of 0.15--0.3 normal nuclear density.

Statistical decay of very hot nuclei-the production of large clusters

Abstract: Heavy ion collisions are the only tools that enable us to reach compressions of nuclear matter up to a factor of about three. Theories of the collision dynamics that are necessary in order to extract the equation of state for nuclear matter are discussed. The main part of the review is devoted to the statistical decay of equilibrised very hot nuclei. A new mathematical method, microcanonical Metropolis sampling, which allows the explicit calculation of microcanonical observables directly out of the microcanonical partition sum with high statistics, is presented. Thermodynamics of finite nuclei can thus be established from the first principles. This is important as nuclei subjected to long-range Coulomb forces do not allow extrapolation to the thermodynamic limit. This peculiarity has interesting consequences for the phase transitions and the critical behaviour of nuclei. It is also related to the property of nuclei to break into large clusters at high excitation.