Enhanced Fusion-Evaporation Cross Sections in Neutron-Rich 132^{132}Sn on 64^{64}Ni

Evaporation residue cross sections have been measured with neutron-rich radioactive $^{132}$Sn beams on $^{64}$Ni in the vicinity of the Coulomb barrier. The average beam intensity was $2\times 10^{4}$ particles per second and the smallest cross section measured was less than 5 mb. Large subbarrier fusion enhancement was observed. Coupled-channels calculations taking into account inelastic excitation and neutron transfer underpredict the measured cross sections below the barrier.Comment: 4 pages including 1 table and 3 figure

Photonuclear fission with quasimonoenergetic electron beams from laser wakefields

Recent advancements in laser wakefield accelerators have resulted in the generation of low divergence, hundred MeV, quasimonoenergetic electron beams. The bremsstrahlung produced by these highly energetic electrons in heavy converters includes a large number of MeV γγ rays that have been utilized to induce photofission in natural uranium. Analysis of the measured delayed γγ emission demonstrates production of greater than 3×1053×105 fission events per joule of laser energy, which is more than an order of magnitude greater than that previously achieved. Monte Carlo simulations model the generated bremsstrahlung spectrum and compare photofission yields as a function of target depth and incident electron energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87815/2/231107_1.pd

Evidence for Thermal Equilibration in Multifragmentation Reactions probed with Bremsstrahlung Photons

The production of nuclear bremsstrahlung photons (E$_{\gamma}>$ 30 MeV) has been studied in inclusive and exclusive measurements in four heavy-ion reactions at 60{\it A} MeV. The measured photon spectra, angular distributions and multiplicities indicate that a significant part of the hard-photons are emitted in secondary nucleon-nucleon collisions from a thermally equilibrated system. The observation of the thermal component in multi-fragment $^{36}$Ar+$^{197}$Au reactions suggests that the breakup of the thermalized source produced in this system occurs on a rather long time-scale.Comment: Revised version, accepted for publication in Physical Review Letters. 4 pages, 4 fig

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

Thermal bremsstrahlung probing the thermodynamical state of multifragmenting systems

Inclusive and exclusive hard-photon (E$_\gamma >$ 30 MeV) production in five different heavy-ion reactions ($^{36}$Ar+$^{197}$Au, $^{107}$Ag, $^{58}$Ni, $^{12}$C at 60{\it A} MeV and $^{129}$Xe+$^{120}$Sn at 50{\it A} MeV) has been studied coupling the TAPS photon spectrometer with several charged-particle multidetectors covering more than 80% of 4$\pi$. The measured spectra, slope parameters and source velocities as well as their target-dependence, confirm the existence of thermal bremsstrahlung emission from secondary nucleon-nucleon collisions that accounts for roughly 20% of the total hard-photon yield. The thermal slopes are a direct measure of the temperature of the excited nuclear systems produced during the reaction.Comment: 4 pages, 3 figures, Proceedings CRIS 2000, 3rd Catania Relativistic Ion Studies, "Phase Transitions in Strong Interactions: Status and Perspectives", Acicastello, Italy, May 22-26, 2000 (to be published in Nuc. Phys. A

Hadronic Excitation of the Giant Dipole Resonance in 208-Pb and 40-Ca at E_p = 200 MeV

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Calibration of Plastic Phoswich Detectors for Charged Particle Detection

The response of an array of plastic phoswich detectors to ions of $1\le Z\le 18$ has been measured from $E/A$=12 to 72 MeV. The detector response has been parameterized by a three parameter fit which includes both quenching and high energy delta-ray effects. The fits have a mean variation of $\le 4\%$ with respect to the data.Comment: 17 pages, 5 figure

Reactions of a Be-10 beam on proton and deuteron targets

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus Be-11 has been examined through the 10Be(d,p) reaction in inverse kinematics at equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of Be-10 on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of Be-10 on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in Be-11 were analyzed using the Finite Range ADiabatic Wave Approximation (FR-ADWA). Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4) respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor.Comment: 16 Pages, 10 figure