Particle spectra from reversed kinematics: Powerful probes of hot rotating nuclei

Abstract

Inclusive 1H/4He emission has been studied for three reactions in "reversed kinematics", 4~ (8.5MeV/u)+~2C. The 4He spectra include the heretofore unobserved region of low c.m. energies in the direction of the heavy reactant. A test of forward-backward symmetry is made for the hot-spot, moving source model; the data do not support the model. Effective emission barriers for 4He evaporation are found to be within ~10~ of the corresponding fusion barriers, while for ~H evaporation the emission barriers are more than 25 ~o lower. It is possible that deformations predicted by the rotating liquid drop model can account for the 4He evaporation spectra, but substantial change in the standard evaporation treatment is required to explain the spectra for ~H.

Charged-particle evaporation from hot composite nuclei: Evidence over a broadZrange for distortions from cold nuclear profiles

“…Using very heavy-ion beams in reversed kinematics [35], the large center-of-mass velocities served as a booster which greatly increased the particle energies in the forward hemisphere. This feature, together with the use of relatively-low-threshold detector systems, often permitted recording the particle spectra down to very low c.m.…”

“…Hence it is apparent that both the energy spectra and the angular distributions are needed in the search for a consistent interpretation of the roles of shape, temperature, and spin. Particle evaporation spectra and angular distributions of especially good quality can be obtained for reactions carried out in reversed kinematics [35]. For incident energies of E/ A - 8.5 MeV or lower, full momentum transfer and energy equilibration generally provide the dominant path to composite-nucleus formation.…”

Decay of the compound nucleus179Au formed in the cold fusion reaction90Zr+89Y

“…4 MeV from the isochron cyclotron at Bonn. Employing elastic and inelastic scattering from a mixed C-and Au-target one obtains several discrete lines of known energy covering a range comparable to the energy range in the present fusion experiment.…”

“…In several papers [4,[6][7][8] in which proton emission as well as e-particle emission of hot nuclei was measured simultaneously and interpreted with the computer code GANES [-11], nuclear shapes with axis ratios of 1.7 [4] to 2.5 [8] had to be assumed in order to explain the e-particle data. Even much higher deformations (axis ratio up to 3.0 and more) were necessary to describe the proton spectra at the same time.…”

Fission accompanied by alpha particle emission in the12C(85MeV)+232Th reaction

“…Subsequently, the spectra obtained for the C target were multiplied by the ratio described above and then subtracted from the spectra obtained for the Th target at each angle. In this procedure we assumed, on the basis of experimental results of [19,20], that the energy spectra and the angular distributions of alpha particles emitted in the 12C+ 160 and 12C+ 14N reactions do not differ significantly from that obtained in the 12C + 12C reaction. According to our estimates, about 20% of alpha particles were emitted from impurities at 20 ~ Figure 2 shows an example of the alpha spectra used for such corrections at 20 ~ and 120~ the contribution from light element impurities at backward angles is very small.…”