135 research outputs found
Muon-induced neutron production and detection with GEANT4 and FLUKA
We report on a comparison study of the Monte Carlo packages GEANT4 and FLUKA
for simulating neutron production by muons penetrating deep underground. GEANT4
is found to generate fewer neutrons at muon energies above ~100 GeV, by at most
a factor of 2 in some materials, which we attribute mainly to lower neutron
production in hadronic cascades. As a practical case study, the muon-induced
neutron background expected in a 250 kg liquid-xenon WIMP dark matter detector
was calculated and good agreement was found for the recoil event rates. The
detailed model of neutron elastic scattering in GEANT4 was also shown to
influence the nuclear recoil spectrum observed in the target, which is
presently a shortcoming of FLUKA. We conclude that both packages are suited for
this type of simulation, although further improvements are desirable in both
cases.Comment: (23 pages, 14 figures) To appear in Nucl. Instrum. Meth. A v2:
Changes to format only; v3: Corrected typo in front matter; v4: Looked up
additional experimental data for comparison with simulation
Single-photon emission via Raman scattering from the levels with partially resolved hyperfine structure
The probability of emission of a single photon via Raman scattering of laser
pulse on the three-level - type atom in microcavity is studied. The
duration of the pulse is considered to be short enough, so that the hyperfine
structure of the upper level remains totally unresolved, while that of the
lower level is totally resolved. The coherent laser pulse is assumed to be in
resonance with the transition between one hyperfine structure component of the
lower atomic level and all hyperfine structure components of the upper level,
while the quantized cavity field is assumed to be in resonance with the
transition between the other hyperfine structure component of the lower level
and all components of the upper one. The dependence of the photon emission
probability on the mutual orientation of polarization vectors of the cavity
mode and of the coherent laser pulse is analyzed. Particularly, the case is
investigated, when the total electronic angular momentum of the lower atomic
level equals 1/2, which is true for the ground states of alkali atoms employed
in the experiments on deterministic single photon emission. It is shown, that
in this case the probability of photon emission equals zero for collinear
polarizations of the photon and of the laser pulse, and the probability obtains
its maximum value, when the angle between their polarizations equals 60
degrees.Comment: 5 pages, 3 figure
Isovector soft dipole mode in 6Be
By using the 1H(6Li,6Be)n charge-exchange reaction, continuum states in 6Be
were populated up to E_t=16 MeV, E_t being the 6Be energy above its three-body
decay threshold. In kinematically complete measurements performed by detecting
alpha+p+p coincidences, an E_t spectrum of high statistics was obtained,
containing approximately ~5x10^6 events. The spectrum provides detailed
correlation information about the well-known 0^+ ground state of 6Be at
E_t=1.37 MeV and its 2^+ state at E_t=3.05 MeV. Moreover, a broad structure
extending from 4 to 16 MeV was observed. It contains negative parity states
populated by Delta L=1 angular momentum transfer without other significant
contributions. This structure can be interpreted as a novel phenomenon, i.e.
the isovector soft dipole mode associated with the 6Li ground state. The
population of this mode in the charge-exchange reaction is a dominant
phenomenon for this reaction, being responsible for about 60% of the cross
section obtained in the measured energy range.Comment: 8 pages, 7 figure
Accurate spline solutions of the Dirac equation with parity-nonconserving potential
The complete system of the B-spline solutions for the Dirac equation with the
parity-nonconserving (PNC) weak interaction effective potential is obtained.
This system can be used for the accurate evaluation of the radiative
corrections to the PNC amplitudes in the multicharged ions and neutral atoms.
The use of the scaling procedure allows for the evaluation of the PNC matrix
elements with relative accuracy .Comment: 7 page
Combined effect of coherent Z exchange and the hyperfine interaction in atomic PNC
The nuclear spin-dependent parity nonconserving (PNC) interaction arising
from a combination of the hyperfine interaction and the coherent,
spin-independent, PNC interaction from Z exchange is evaluated using many-body
perturbation theory. For the 6s-7s transition in 133Cs, we obtain a result that
is about 40% smaller than that found previously by Bouchiat and Piketty [Phys.
Lett. B 269, 195 (1991)]. Applying this result to 133Cs, leads to an increase
in the experimental value of nuclear anapole moment and exacerbates differences
between constraints on PNC meson coupling constants obtained from the Cs
anapole moment and those obtained from other nuclear parity violating
experiments. Nuclear spin-dependent PNC dipole matrix elements, including
contributions from the combined weak-hyperfine interaction, are also given for
the 7s-8s transition in 211Fr and for transitions between ground-state
hyperfine levels in K, Rb, Cs, Ba+, Au, Tl, Fr, and Ra+.Comment: Revtex4 preprint 19 pages 4 table
Calculation of nuclear spin-dependent parity-nonconserving amplitude for (7s,F=4) --> (7s,F=5) transition in Fr
Many-body calculation of nuclear spin-dependent parity-nonconserving
amplitude for (7s,F=4) --> (7s,F=5) transition between hyperfine sublevels of
the ground state of Fr is carried out. The final result is <7s,F=5
||d_PNC|| 7s,F=4> = -0.49 10^{-10} i kappa a.u., where kappa is the
dimensionless coupling constant. This is approximately an order of magnitude
larger than similar amplitude in Cs. The dominant contribution to kappa is
associated with the anapole moment of the nucleus.Comment: 4 pages, submitted to Phys.Rev.
Simulation of neutrons produced by high-energy muons underground
This article describes the Monte Carlo simulation used to interpret the
measurement of the muon-induced neutron flux in the Boulby Underground
Laboratory (North Yorkshire, UK), recently performed using a large scintillator
veto deployed around the ZEPLIN-II WIMP detector. Version 8.2 of the GEANT4
toolkit was used after relevant benchmarking and validation of neutron
production models. In the direct comparison between Monte Carlo and
experimental data, we find that the simulation produces a 1.8 times higher
neutron rate, which we interpret as over-production in lead by GEANT4. The
dominance of this material in neutron production allows us to estimate the
absolute neutron yield in lead as (1.31 +/- 0.06) x 10^(-3)
neutrons/muon/(g/cm^2) for a mean muon energy of 260 GeV. Simulated nuclear
recoils due to muon-induced neutrons in the ZEPLIN-II target volume (~1 year
exposure) showed that, although a small rate of events is expected from this
source of background in the energy range of interest for dark matter searches,
no event survives an anti-coincidence cut with the veto.Comment: 13 Pages, 11 Figures, 3 Tables. To appear in Astroparticle Physics.
Version 2 has minor corrections and clarifications. Figures 1 and 3 now
include neutron yields obtained with FLUKA-200
QED Effects in Heavy Few-Electron Ions
Accurate calculations of the binding energies, the hyperfine splitting, the
bound-electron g-factor, and the parity nonconservation effects in heavy
few-electron ions are considered. The calculations include the relativistic,
quantum electrodynamic (QED), electron-correlation, and nuclear effects. The
theoretical results are compared with available experimental data. A special
attention is focused on tests of QED in a strong Coulomb field.Comment: 28 pages, 6 tables, 5 figure
GABRIELA : a new detector array for gamma-ray and conversion electron spectroscopy of transfermium elements
With the aid of the Geant4 Monte Carlo simulation package a new detection
system has been designed for the focal plane of the recoil separator VASSILISSA
situated at the Flerov Laboratory of Nuclear Reactions, JINR, Dubna. GABRIELA
(Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyser
VASSILISSA) has been optimised to detect the arrival of reaction products and
their subsequent radioactive decays involving the emission of alpha- and
beta-particles, fission fragments, gamma- and X-rays, and conversion electrons.
The new detector system is described and the results of the first commissioning
experiments are presented.Comment: 24 pages, Submitted to NIM
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