Synthesis of new neutron-rich heavy nuclei: An experimentalist's view

I attempt to experimentally evaluate the prospects of synthesizing new neutron- rich superheavy nuclei. I consider three possible synthetic paths to neutron- rich superheavy nuclei: (a) the use of neutron-rich radioactive beams. (b) the use of damped collisions and (c) the use of multi-nucleon transfer reactions. I consider the prospects of synthesizing new n-rich isotopes of Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB and SPIRAL2. For the damped collision path, I present the results of a study of a surrogate reaction, 160Gd + 186W. These data indicate the formation of Au (trans-target) fragments and the depletion of yields of target-like fragments by fission and fragment emission. The data are compared to predictions of Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of a study of the 136Xe + 208Pb reaction are discussed. I consider the possibility of multi-nucleon transfer reactions with radioactive beams

Surface Morphology and Phase Stability of Titanium Foils Irradiated by 136 MeV 136Xe

A stack of titanium foils was irradiated with 136 MeV 136Xe to study microstructure damage and phase stability of titanium upon irradiation. X- ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and atomic force microscopy were used to study the resulting microstructure damage and phase stability of titanium. We observed the phase transfor- mation of polycrystalline titanium from alpha-Ti (hexagonally closed packed (hcp)) to face centered cubic (fcc) after irradiation with 2.2 x 1015 ions/cm2. Irradiation of Ti with 1.8 x 1014-2.2 x 1015 ions/cm2 resulted in the forma- tion of voids, hillocks, dislocation loops, dislocation lines, as well as polygonal ridge networks

Heavy Residue Formation in 20 MeV/nucleon 197Au + 90Zr collisions

The yields and velocity distributions of heavy residues and fission fragments from the reaction of 20 MeV/nucleon 197Au + 90Zr have been measured using the MSU A1200 fragment separator. A bimodal distribution of residues is observed, with one group, resulting from peripheral collisions, having fragment mass numbers A=160-200, while the other group, resulting from ``hard'' collisions, has A=120-160. This latter group of residues can be distinguished from fission fragments by their lower velocities. A model combining deep-inelastic transfer and incomplete fusion for the primary interaction stage and a statistical evaporation code for the deexcitation stage has been used to describe the properties of the product distributions.Comment: 19 pages, 6 figures, preprint submitted to Nucl. Phys.

Measurement of the Survival Probabilities for Hot Fusion Reactions

We have studied the fission-neutron emission competition in highly excited $^{274}$Hs (Z=108) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments ($^{26}$Mg + $^{248}$Cm and $^{25}$Mg + $^{248}$Cm) were used to identify the properties of first chance fission of $^{274}$Hs. A Harding-Farley analysis of the fission neutrons emitted in the $^{25,26}$Mg + $^{248}$Cm was performed to identify the pre- and post-scission components of the neutron multiplicities in each system. ($\Gamma$$_{n}$/$\Gamma$$_{t}$) for the first chance fission of $^{274}$Hs (E$^{\ast}$ = 63 MeV) is 0.89 $\pm$ 0.13, i.e., $\sim$ 90 $$ of the highly excited nuclei survive.The high value of that survival probability is due to dissipative effects during de-excitation. A proper description of the survival probabilities of excited superheavy nuclei formed in hot fusion reactions requires consideration of both dynamic and static (shell-related) effects

Neutron-rich rare isotope production from projectile fission of heavy beams in the energy range of 20 MeV/nucleon

We investigate the possibilities of producing neutron-rich nuclides in projectile fission of heavy beams in the energy range of 20 MeV/nucleon expected from low-energy facilities. We report our efforts to theoretically describe the reaction mechanism of projectile fission following a multinucleon transfer collision at this energy range. Our calculations are mainly based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The deexcitation/fission of the hot heavy projectile fragments is performed with the Statistical Mul- tifragmentation Model (SMM). We compared our model calculations with our previous experimental projectile-fission data of 238U (20 MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall reasonable agreement. Our study suggests that projectile fission following periph- eral heavy-ion collisions at this energy range offers an effective route to access very neutron-rich rare isotopes toward and beyond the astrophysical r-process path

Fusion of radioactive 132^{132}Sn with 64^{64}Ni

Evaporation residue and fission cross sections of radioactive $^{132}$Sn on $^{64}$Ni were measured near the Coulomb barrier. A large sub-barrier fusion enhancement was observed. Coupled-channel calculations including inelastic excitation of the projectile and target, and neutron transfer are in good agreement with the measured fusion excitation function. When the change in nuclear size and shift in barrier height are accounted for, there is no extra fusion enhancement in $^{132}$Sn+$^{64}$Ni with respect to stable Sn+$^{64}$Ni. A systematic comparison of evaporation residue cross sections for the fusion of even $^{112-124}$Sn and $^{132}$Sn with $^{64}$Ni is presented.Comment: 9 pages, 11 figure