653 research outputs found
Destruction of the cosmic γ-ray emitter 26Al in massive stars: Study of the key 26Al (n,α) reaction
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
Long range absorption in the scattering of 6He on 208Pb and 197Au at 27 MeV
Quasi-elastic scattering of 6He at E_lab=27 MeV from 197Au has been measured
in the angular range of 6-72 degrees in the laboratory system employing LEDA
and LAMP detection systems. These data, along with previously analysed data of
6He + 208Pb at the same energy, are analyzed using Optical Model calculations.
The role of Coulomb dipole polarizability has been investigated. Large
imaginary diffuseness parameters are required to fit the data. This result is
an evidence for long range absorption mechanisms in 6He induced reactions.Comment: 10 pages, 10 figures, minor corrections. To appear in Nucl. Phys.
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
Neutron-induced background by an alpha-beam incident on a deuterium gas target and its implications for the study of the 2H(alpha,gamma)6Li reaction at LUNA
The production of the stable isotope Li-6 in standard Big Bang
nucleosynthesis has recently attracted much interest. Recent observations in
metal-poor stars suggest that a cosmological Li-6 plateau may exist. If true,
this plateau would come in addition to the well-known Spite plateau of Li-7
abundances and would point to a predominantly primordial origin of Li-6,
contrary to the results of standard Big Bang nucleosynthesis calculations.
Therefore, the nuclear physics underlying Big Bang Li-6 production must be
revisited. The main production channel for Li-6 in the Big Bang is the
2H(alpha,gamma)6Li reaction. The present work reports on neutron-induced
effects in a high-purity germanium detector that were encountered in a new
study of this reaction. In the experiment, an {\alpha}-beam from the
underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium
gas target are used. A low neutron flux is induced by energetic deuterons from
elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the
ultra-low laboratory neutron background at LUNA, the effect of this weak flux
of 2-3 MeV neutrons on well-shielded high-purity germanium detectors has been
studied in detail. Data have been taken at 280 and 400 keV alpha-beam energy
and for comparison also using an americium-beryllium neutron source.Comment: Submitted to EPJA; 13 pages, 8 figure
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
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