First on-line results for As and F beams from HRIBF target/ion sources

The first on-line tests of the ion sources to provide radioactive ion beams of 69/7OAs and 17>18F for the Holifield Radioactive Ion Beam Facility have been performed using the UNISOR facility at HRIBF. For 70As the measured efficiency is 0.8+ 0.3% with a hold-up time of 3.6 ± 0.3 hours as measured with ^As at a target temperature of 1270°C. For 17F the efficiency for A117F is 0.0024 + 0.0008% with a hold-up time of 16.4 + 0.8 m as measured with A118F at a target temperature of 1470°C

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

Electromagnetic properties of the 21+ state in 134Te: Influence of core excitation on single-particle orbits beyond 132Sn

The g factor and B(E2) of the first excited 2+ state have been measured following Coulomb excitation of the neutron-rich semimagic nuclide 134Te (two protons outside 132Sn) produced as a radioactive beam. The precision achieved matches related g-factor m

Segmented YSO scintillation detectors as a new β-implant detection tool for decay spectroscopy in fragmentation facilities

A newly developed segmented YSO scintillator detector was implemented for the first time at the RI-beam Factory at RIKEN Nishina Center as an implantation-decay counter. The results from the experiment demonstrate that the detector is a viable alternative to conventional silicon-strip detectors with its good timing resolution and high detection efficiency for β particles. A Position-Sensitive Photo-Multiplier Tube (PSPMT) is coupled with a 48 × 48 segmented YSO crystal. To demonstrate its capabilities, a known short-lived isomer in Ni and the β decay of Co were measured by implanting those ions into the YSO detector. The half-lives and γ-rays observed in this work are consistent with the known values. The β-ray detection efficiency is more than 80 % for the decay of Co.The present experiment was carried out at the RI Beam Factory operated by RIKEN Nishina Center, RIKEN and CNS, University of Tokyo. This research was supported in part by the Offce of Nuclear Physics, U.S. Department of Energy under Award No. DE-FG02-96ER40983 (UTK)

S-wave scattering lengths for the Be 7 +p system from an R-matrix analysis

The astrophysical S factor for the radiative proton capture reaction on Be7 (S17) at low energies is affected by the s-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the Be7+p system in the center-of-mass energy range 0.474-2.740 MeV and center-of-mass angular range 70-150. A radioactive Be7 beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH2)n target. Scattered ions were detected in the segmented Silicon Detector Array. Using an R-matrix analysis of ORNL and Louvain-la-Neuve cross-section data, the s-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34-1.33+1.11 and -3.18-0.50+0.55 fm, respectively. The uncertainty in the s-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in S17 at zero energy. The level structure of B8 is discussed based upon the results from this work. Evidence for the existence of 0+ and 2+ levels in B8 at 1.9 and 2.21 MeV, respectively, is observed

A statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy

Multifragment emission following Xe+Au collisions at 30, 40, 50 and 60 AMeV has been studied with multidetector systems covering nearly 4-pi in solid angle. The correlations of both the intermediate mass fragment and light charged particle multiplicities with the transverse energy are explored. A comparison is made with results from a similar system, Xe+Bi at 28 AMeV. The experimental trends are compared to statistical model predictions.Comment: 7 pages, submitted to Phys. Rev.

First on-line results for As and F beams from HRIBF target/ion sources

The first on-line tests of the ion sources to provide radioactive ion beams of {sup 69,70}As and {sup 17,18}F for the Holifield Radioactive Ion Beam Facility (HRIBF) have been performed using the UNISOR facility at HRIBF. The target/ion source is an electron beam plasma (EBP) source similar to the ISOLDE design. The measured efficiencies for {sup 69}As and {sup 70}AS were 0.5 {+-} 0.2% and 0.8 {+-} 0.3%, respectively. The arsenic hold-up time in the tested target ion source was 3.6 {+-} 0.3 hours as measured with {sup 72}As at a target temperature of 1300 {degrees}C. The measured efficiencies for {sup 17}F and {sup 18}F were 0.0052 {+-} 0.0008% and 0.06 {+-} 0.02%, respectively. The source hold-up time for fluorine was measured with Al{sup 18}F since 88% of the observed radioactive fluorine was found in this molecule. The Al{sup 18}F hold-up time was 16.4 {+-} 0.8 minutes at a target temperature of 1470 {degrees}C

Neutron-rich isotope production using the uranium carbide multi-foil SPES target prototype

In the framework of the R&D program for the SPES (Selective Production of Exotic Species) project of the Istituto Nazionale di Fisica Nucleare (INFN), production yields of neutron-rich isotopes have been measured at the Holifield Radioactive Ion Beam Facility (HRIBF, Oak Ridge National Laboratory, USA). This experiment makes use of the multi-foil SPES target prototype composed of 7 uranium carbide discs, with excess of graphite (ratio C/U = 4 . 77 isotopes of medium mass (between 72 and 141amu), produced via proton-induced fission of uranium using a 40MeV proton beam, have been collected and analyzed for the target heated at 2000 ° C target temperature

A new look at reaction mechanisms with 4. pi. charged-particle and neutron multiplicity measurements

We have studied the excitation of target-like fragments produced in the reactions of 331.9 MeV /sup 28/Si + /sup 181/Ta. The light charged particles and intermediate mass fragments were detected in a small, highly segmented 4..pi.. phoswich detector system placed inside the spin spectrometer, a 4..pi.. NaI array which served as a neutron and ..gamma..-ray detector. All target emissions indicate that excitation ceases to increase with decreasing projectile-like fragment energy, as it should if the primary reaction is binary. Non-equilibrium neutron, proton and ..cap alpha..-particle emission and projectile fragmentation conspire and limit the conversion of kinetic energy into target excitation. This effect is more pronounced for PLF away from the injection point and for the largest kinetic energy losses. 8 refs., 10 figs

Fragment excitation energies at freeze-out in 84^{84}Kr+93^{93}Nb collisions at 45 MeV/nucleon

International audienceThe emission of light charged particles and intermediate-mass fragments (IMF’s) from central collisions of 45 MeV/nucleon 84Kr with 93Nb has been studied. Violent collisions have been selected using the total collected charge condition. The analysis of the primary IMF excitation energies has been performed for four bins of the detected IMF charge (2<ZIMF<20). We find evidence that (a) the mean excitation energy per nucleon for these fragments is independent of fragment charge and approximately equal to 2.5 MeV, (b) the primary fragments at freeze-out preserve the entrance channel (combined system) N/Z ratio, and (c) the freeze-out volume itself is far from spherical