I. Diószegi

Quasifission reactions as a probe of nuclear viscosity

Fission fragment mass and angular distributions were measured from the ^{64}Ni+^{197}Au reaction at 418 MeV and 383 MeV incident energy. A detailed data analysis was performed, using the one-body dissipation theory implemented in the code HICOL. The effect of the window and the wall friction on the experimental observables was investigated. Friction stronger than one-body was also considered. The mass and angular distributions were consistent with one-body dissipation. An evaporation code DIFHEAT coupled to HICOL was developed in order to predict reaction time scales required to describe available data on pre-scission neutron multiplicities. The multiplicity data were again consistent with one-body dissipation. The cross-sections for touch, capture and quasi-fission were also obtained.

An electron-positron pair spectrometer for high energy decays of nuclei

A highly segmented phoswich array of plastic scintillators has been constructed for measurements of (e+, e−) pairs emitted in high energy electromagnetic transitions in nuclei. Electron (positron) energies of 2–30 MeV can be measured by each individual element, with a total transition energy resolution of δEE = 13% for a 20 MeV transition. The array covers 29% of 4π and its efficiency is 1.6% for a 6 MeV E0 internal pair decay, and 1.1% for an 18 MeV E1 transition. These efficiency values include cuts which reduce background and optimize energy resolution. Experimental results are compared with GEANT simulations demonstrating the detectors ability to determine transition multipolarities.

Nuclear viscosity of hot rotating 240Cf

In a detailed investigation of giant dipole resonance (GDR) γ-ray yield from 240Cf populated in the 32S + 208Pb reaction, the absolute γ-ray/fission multiplicities are extracted over a wide range of excitation energy and angular momentum. The enhanced yield of GDR decay γ rays has been analyzed within the framework of a modified statistical model containing the nuclear viscosity as a free parameter. The extracted nuclear dissipation coefficient is found to be independent of the temperature. Large constant dissipation during the saddle-to-scission path provides good fits to the γ-ray spectra.

The High Energy Photons From Very Symmetric Reactions: The Giant Dipole Resonance In 179Au Nucleus

High‐energy γ rays emitted in the symmetric reaction 90Zr + 89Y have been measured at the Argonne National Laboratory using the LEPPEX array coupled to the Fragment Mass Analyzer (FMA). The high‐energy γ‐ray spectra emitted by the giant dipole resonance built on excited states and associated with the evaporation of 0, 1 and 2 nucleons have been measured. The statistical model analysis indicates that the radiative‐fusion process, namely the 0 particle emission channel, can be well described as a compound nucleus decay channel. In addition, the analysis of the high‐energy γ‐ray spectra associated with the different evaporation channels provides the first evidence that shell effects still play a role in determining the nuclear shapes of 179Au in the temperature interval 0.5–1 MeV.