378 research outputs found
On the β-detection efficiency of a combined Si and plastic stack detector for DESPEC
A Geant4 simulation has been carried out in order to determine the B-detection efficiency of a rare isotope
beam implantation setup, for decay spectroscopy experiments, comprising a number of Double Sided Silicon
Strip Detectors (DSSSDs) and two plastic scintillation detectors placed upstream and downstream. The
absolute efficiency for the emitted B-particle detection from radioactive fragments implanted in the DSSSDs
using fast-timing plastic-scintillator detector, is calculated. The detection efficiency of the setup has been
studied with two different distances between the Si layers and plastics. The requirement for the thickness of
the Si detector layers and its implication on the B-detection effciency has been investigated for 1 mm and
300 um thickness of Si layers. The combined efficiency of DSSSD and plastic detectors were also simulated
for two different thicknesses of the DSSSD
Measurement of the 18Ne(a,p_0)21Na reaction cross section in the burning energy region for X-ray bursts
The 18Ne(a,p)21Na reaction provides one of the main HCNO-breakout routes into
the rp-process in X-ray bursts. The 18Ne(a,p_0)21Na reaction cross section has
been determined for the first time in the Gamow energy region for peak
temperatures T=2GK by measuring its time-reversal reaction 21Na(p,a)18Ne in
inverse kinematics. The astrophysical rate for ground-state to ground-state
transitions was found to be a factor of 2 lower than Hauser-Feshbach
theoretical predictions. Our reduced rate will affect the physical conditions
under which breakout from the HCNO cycles occurs via the 18Ne(a,p)21Na
reaction.Comment: 5 pages, 3 figures, accepted for publication on Physical Review
Letter
Tensor analyzing powers for Li7 breakup
Differential cross sections and T20 and 20TT analyzing powers have been measured for 70 MeV Li7 breakup into the particle plus triton channel, on a Sn120 target. Measurements were made for both continuum breakup and sequential breakup via the 4.63 MeV state in Li7. The T20 data for the continuum breakup do not agree with a semiclassical Coulomb model, indicating that the breakup at small angles does not proceed solely via a Coulomb force. The data generally show a somewhat better agreement with continuum discretized coupled channels calculations, indicating the importance of the nuclear force and channel coupling in the reaction mechanism. © 1995 The American Physical Society
Coulomb excitation of 73Ga
The B(E2; Ii -> If) values for transitions in 71Ga and 73Ga were deduced from
a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using
post-accelerated beams of 71,73Ga at the REX-ISOLDE on-line isotope mass
separator facility. The emitted gamma rays were detected by the
MINIBALL-detector array and B(E2; Ii->If) values were obtained from the yields
normalized to the known strength of the 2+ -> 0+ transition in the 120Sn
target. The comparison of these new results with the data of less neutron-rich
gallium isotopes shows a shift of the E2 collectivity towards lower excitation
energy when adding neutrons beyond N = 40. This supports conclusions from
previous studies of the gallium isotopes which indicated a structural change in
this isotopical chain between N = 40 and N = 42. Combined with recent
measurements from collinear laser spectroscopy showing a 1/2- spin and parity
for the ground state, the extracted results revealed evidence for a 1/2-; 3/2-
doublet near the ground state in 73 31Ga42 differing by at most 0.8 keV in
energy
Coulomb excitation of Ni at safe energies
The value in Ni has been measured using Coulomb
excitation at safe energies. The Ni radioactive beam was
post-accelerated at the ISOLDE facility (CERN) to 2.9 MeV/u. The emitted
rays were detected by the MINIBALL detector array. A kinematic
particle reconstruction was performed in order to increase the measured c.m.
angular range of the excitation cross section. The obtained value of
2.8 10 efm is in good agreement with the value
measured at intermediate energy Coulomb excitation, confirming the low
transition probability.Comment: 4 pages, 5 figure
The Single-Particle Structure of Neutron-Rich Nuclei of Astrophysical Interest at the Ornl Hribf
The rapid nuetron-capture process (r process) produces roughly half of the
elements heavier than iron. The path and abundances produced are uncertain,
however, because of the lack of nuclear strucure information on important
neutron-rich nuclei. We are studying nuclei on or near the r-process path via
single-nucleon transfer reactions on neutron-rich radioactive beams at ORNL's
Holifield Radioactive Ion Beam Facility (HRIBF). Owing to the difficulties in
studying these reactions in inverse kinematics, a variety of experimental
approaches are being developed. We present the experimental methods and initial
results.Comment: Proceedings of the Third International Conference on Fission and
Properties of Neutron-Rich Nucle
Prototyping of DSSDs for Particle Tracking and Spectroscopy within the EXL Project at Fair
Prototype double-sided silicon strip detectors (DSSD) of 300 m thickness produced at PTI St. Petersburg (Russia) were tested for the use as position sensitive, and E detectors for tracking and particle identification in the EXL (EXotic nuclei studied in Light-ion induced reactions at the NESR storage ring) setup at the FAIR (Facility for Antiproton and Ion Research) project at GSI. We describe the characteristics of detectors with and strips, respectively. The response of these detectors for Am particles injected either from the p or n side was examined. The test measurements were performed partially at GSI and the University of Edinburgh. A first in-beam test with a proton beam of 50 MeV with the latter two DSSDs and two 6.5 mm thick Si(Li) detectors was also done at KVI Groningen, the Netherlands. The results reveal good spectroscopic properties of these detectors
Resonances in 19Ne with relevance to the astrophysically important 18F(p,{\alpha})15O reaction
The most intense gamma-ray line observable from novae is likely to be from
positron annihilation associated with the decay of 18F. The uncertainty in the
destruction rate of this nucleus through the 18F(p,{\alpha})15O reaction
presents a limit to interpretation of any future observed gamma-ray flux.
Direct measurements of the cross section of both this reaction and the
18F(p,p)18F reaction have been performed between center of mass energies of 0.5
and 1.9 MeV. Simultaneous fits to both data sets with the R-Matrix formalism
reveal several resonances, with the inferred parameters of populated states in
19Ne in general agreement with previous measurements. Of particular interest,
extra strength has been observed above ECM \sim1.3 MeV in the 18F(p,p)18F
reaction and between 1.3-1.7 MeV in the 18F(p,{\alpha})15O reaction. This is
well described by a broad 1/2+ state, consistent with both a recent theoretical
prediction and an inelastic scattering measurement. The astrophysical
implications of a broad sub-threshold partner to this state are discussed.Comment: 7 pages, 4 figures, 2 table
Indirect study of 19Ne states near the 18F+p threshold
The early E < 511 keV gamma-ray emission from novae depends critically on the
18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O
reaction is still largely uncertain due to the unknown strengths of low-lying
proton resonances near the 18F+p threshold which play an important role in the
nova temperature regime. We report here our last results concerning the study
of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that
these two low-lying resonances cannot be neglected. These results are then used
to perform a careful study of the remaining uncertainties associated to the
18F(p,a)15O and 18F(p,g)19Ne reaction rates.Comment: 18 pages, 8 figures. Accepted in Nuclear Physics
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