2,549 research outputs found
Dynamical approach to heavy-ion induced fission using actinide target nuclei at energies around the Coulomb barrier
In order to describe heavy-ion fusion reactions around the Coulomb barrier
with an actinide target nucleus, we propose a model which combines the
coupled-channels approach and a fluctuation-dissipation model for dynamical
calculations. This model takes into account couplings to the collective states
of the interacting nuclei in the penetration of the Coulomb barrier and the
subsequent dynamical evolution of a nuclear shape from the contact
configuration. In the fluctuation-dissipation model with a Langevin equation,
the effect of nuclear orientation at the initial impact on the prolately
deformed target nucleus is considered. Fusion-fission, quasi-fission and deep
quasi-fission are separated as different Langevin trajectories on the potential
energy surface. Using this model, we analyze the experimental data for the mass
distribution of fission fragments (MDFF) in the reactions of
S+U and Si+U at several incident energies
around the Coulomb barrier. We find that the time scale in the quasi-fission as
well as the deformation of fission fragments at the scission point are
different between the Si+U and S+U systems,
causing different mass asymmetries of the quasi-fission.Comment: 11 figure
Coupling transport and biodegradation of VOCs in surface and subsurface soils.
Volatile organic chemicals present at Superfund sites preferentially partition into the soil gas and may be available for microbial degradation. A simple mass transfer model for biodegradation for volatile substrates has been developed for the aerobic decomposition of aromatic and aliphatic hydrocarbons. The mass transfer analysis calculates diffusive fluxes from soil gas through water and membrane films and into the cell. This model predicts an extreme sensitivity of potential biodegradation rates to the air-water partition coefficients of the compounds. Aromatic hydrocarbons are removed rapidly while the aliphatic hydrocarbons are much slower by orders of magnitude. Furthermore, oxygen transfer is likely to limit aromatic hydrocarbon degradation rates. The model presents results that cast doubt on the practicality of using methane or propane for the co-metabolic destruction of trichloroethylene in a gas phase bioreactor. Toluene as a primary substrate has better mass transfer characteristics to achieve more efficient trichloroethylene degradation. Hence, in sites where these contaminants coexist, bioremediation could be improved
Isospin symmetry breaking in an algebraic pairing Sp(4) model
An exactly solvable sp(4) algebraic approach extends beyond the traditional
isospin conserving nuclear interaction to bring forward effects of isospin
symmetry breaking and isospin mixing resulting from a two-body nuclear
interaction that includes proton-neutron (pn) and like-particle isovector
pairing correlations plus significant isoscalar pn interactions. The model
yields an estimate for the extent to which isobaric analog 0+ states in light
and medium mass nuclei may mix with one another and reveals possible, but still
extremely weak, non-analog beta-decay transitions.Comment: 8 pages, 2 figure
Ground state magnetic dipole moment of 35K
The ground state magnetic moment of 35K has been measured using the technique
of nuclear magnetic resonance on beta-emitting nuclei. The short-lived 35K
nuclei were produced following the reaction of a 36Ar primary beam of energy
150 MeV/nucleon incident on a Be target. The spin polarization of the 35K
nuclei produced at 2 degrees relative to the normal primary beam axis was
confirmed. Together with the mirror nucleus 35S, the measurement represents the
heaviest T = 3/2 mirror pair for which the spin expectation value has been
obtained. A linear behavior of gp vs. gn has been demonstrated for the T = 3/2
known mirror moments and the slope and intercept are consistent with the
previous analysis of T = 1/2 mirror pairs.Comment: 14 pages, 5 figure
Rotational Bands and Electromagnetic Transitions of some even-even Neodymium Nuclei in J-Projected Hartree-Fock Model
Rotational structures of even-even Nd nuclei are studied with the
self-consistent deformed Hartree-Fock (HF) and angular momentum (J) projection
model. Spectra of ground band, recently observed , and a few
more excited, positive and negative parity bands have been studied upto high
spin values. Apart from these detailed electromagnetic properties (like E2, M1
matrix elements) of all the bands have been obtained. There is substantial
agreement between our model calculations and available experimental data.
Predictions are made about the band structures and electromagnetic properties
of these nuclei. Some 4-qasiparticle K-isomeric bands and their electromagnetic
properties are predicted.Comment: 20 page
Electric Dipole Moments of Neutron-Odd Nuclei
The electric dipole moments (EDMs) of neutron-odd nuclei with even protons
are systematically evaluated. We first derive the relation between the EDM and
the magnetic moment operators by making use of the core polarization scheme.
This relation enables us to calculate the EDM of neutron-odd nuclei without any
free parameters. From this calculation, one may find the best atomic system
suitable for future EDM experiments.Comment: 4 page
Coherent photonuclear reactions for isotope transmutation
Coherent photonuclear isotope transmutation (CPIT) produces exclusively
radioactive isotopes (RIs) by coherent photonuclear reactions via E1 giant
resonances. Photons to be used are medium energy photons produced by laser
photons backscattered off GeV electrons. The cross sections are as large as 0.2
- 0.6 b, being independent of individual nuclides. A large fraction of photons
is effectively used for the photonuclear reactions, while the scattered GeV
electrons remain in the storage ring to be re-used. CPIT with medium energy
photons provides specific/desired RIs with the high rate and the high density
for nuclear science, molecular biology and for nuclear medicines.Comment: 8 pages, 2 figure
Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th
Evidence for the existence of a superheavy nucleus with atomic mass number
A=292 and abundance (1-10)x10^(-12) relative to 232Th has been found in a study
of natural Th using inductively coupled plasma-sector field mass spectrometry.
The measured mass matches the predictions [1,2] for the mass of an isotope with
atomic number Z=122 or a nearby element. Its estimated half-life of t1/2 >=
10^8 y suggests that a long-lived isomeric state exists in this isotope. The
possibility that it might belong to a new class of long-lived high spin super-
and hyperdeformed isomeric states is discussed.[3-6]Comment: 14 pages, 5 figure
Perceptions of vulnerability to a future outbreak: a study of horse managers affected by the first Australian equine influenza outbreak
Background A growing body of work shows the benefits of applying social cognitive behavioural theory to investigate infection control and biosecurity practices. Protection motivation theory has been used to predict protective health behaviours. The theory outlines that a perception of a lack of vulnerability to a disease contributes to a reduced threat appraisal, which results in poorer motivation, and is linked to poorer compliance with advised health protective behaviours. This study, conducted following the first-ever outbreak of equine influenza in Australia in 2007, identified factors associated with horse managers’ perceived vulnerability to a future equine influenza outbreak. Results Of the 200 respondents, 31.9% perceived themselves to be very vulnerable, 36.6% vulnerable and 31.4% not vulnerable to a future outbreak of equine influenza. Multivariable logistic regression modelling revealed that managers involved in horse racing and those on rural horse premises perceived themselves to have low levels of vulnerability. Managers of horse premises that experienced infection in their horses in 2007 and those seeking infection control information from specific sources reported increased levels of perceived vulnerability to a future outbreak. Conclusion Different groups across the horse industry perceived differing levels of vulnerability to a future outbreak. Increased vulnerability contributes to favourable infection control behaviour and hence these findings are important for understanding uptake of recommended infection control measures. Future biosecurity communication strategies should be delivered through information sources suitable for the horse racing and rural sectors. Keywords: Equine influenza Perceived vulnerability Protection motivation theory Infection control Biosecurity Emergency animal diseaseThe Rural Industries Research and Development Corporation (RIRDC) funded this researc
The beta-decay of 22Al
In an experiment performed at the LISE3 facility of GANIL, we studied the
decay of 22Al produced by the fragmentation of a 36Ar primary beam. A
beta-decay half-life of 91.1 +- 0.5 ms was measured. The beta-delayed one- and
two-proton emission as well as beta-alpha and beta-delayed gamma decays were
measured and allowed us to establish a partial decay scheme for this nucleus.
New levels were determined in the daughter nucleus 22Mg. The comparison with
model calculations strongly favours a spin-parity of 4+ for the ground state of
22Al
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