111 research outputs found
Enhanced Fusion-Evaporation Cross Sections in Neutron-Rich Sn on Ni
Evaporation residue cross sections have been measured with neutron-rich
radioactive Sn beams on Ni in the vicinity of the Coulomb
barrier. The average beam intensity was 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 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
Ar+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
Thermal bremsstrahlung probing the thermodynamical state of multifragmenting systems
Inclusive and exclusive hard-photon (E 30 MeV) production in five
different heavy-ion reactions (Ar+Au, Ag, Ni,
C at 60{\it A} MeV and Xe+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. 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
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
Recent direct reaction experimental studies with radioactive tin beams
Direct reaction techniques are powerful tools to study the single-particle
nature of nuclei. Performing direct reactions on short-lived nuclei requires
radioactive ion beams produced either via fragmentation or the Isotope
Separation OnLine (ISOL) method. Some of the most interesting regions to study
with direct reactions are close to the magic numbers where changes in shell
structure can be tracked. These changes can impact the final abundances of
explosive nucleosynthesis. The structure of the chain of tin isotopes is
strongly influenced by the Z=50 proton shell closure, as well as the neutron
shell closures lying in the neutron-rich, N=82, and neutron-deficient, N=50,
regions. Here we present two examples of direct reactions on exotic tin
isotopes. The first uses a one-neutron transfer reaction and a low-energy
reaccelerated ISOL beam to study states in 131Sn from across the N=82 shell
closure. The second example utilizes a one-neutron knockout reaction on
fragmentation beams of neutron-deficient 106,108Sn. In both cases, measurements
of gamma rays in coincidence with charged particles proved to be invaluable.Comment: 11 pages, 5 figures, Zakopane Conference on Nuclear Physics "Extremes
of the Nuclear Landscape", Zakopane, Poland, August 31 - September 7, 201
Precision measurement of Zn electron-capture decays with the KDK coincidence setup
Zn is a common calibration source, moreover used as a radioactive
tracer in medical and biological studies. In many cases, -spectroscopy
is a preferred method of Zn standardization, which relies directly on
the branching ratio of via electron capture (EC*). We measure the relative
intensity of this branch to that proceeding directly to the ground state
(EC) using a novel coincidence technique, finding
. Re-evaluating the decay
scheme of Zn by adopting the commonly evaluated branching ratio of
we obtain , and
I_\text{EC^0} = (48.50 \pm 0.06) \%. The associated 1115 keV gamma intensity
agrees with the previously reported NNDC value, and is now accessible with a
factor of ~2 increase in precision. Our re-evaluation removes reliance on the
deduction of this gamma intensity from numerous measurements, some of which
disagree and depend directly on total activity determination. The KDK
experimental technique provides a new avenue for verification or updates to the
decay scheme of Zn, and is applicable to other isotopes.Comment: Uses similar methodology to the 40K measurement by the KDK
Collaboration (Stukel et al PRL 2023, arXiv:2211.10319; Hariasz et al PRC
2023, arXiv:2211.10343), as such there may be some similarity in figures and
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