6,245 research outputs found
X-ray emission from the PSR B1259--63 system near apastron
The PSR B1259--63 system contains a 47 ms radio pulsar in a highly eccentric
binary with a Be-star companion. Strongly time variable X-ray emission was
reported from this system as the pulsar was near apastron in 1992-early 1993.
The variability was primarily deduced from an apparent non-detection of the
\psr system during a first pre-apastron \ros observation in February~1992. We
have re-analyzed the \ros observations of the \psr system. Contrary to the
results of a previous analysis, we find that the \psr system was detected by
\ros during the first off-axis February~1992 observation. The intensity of the
soft X-ray emission of the \psr system before and after the 1992 apastron
appears to vary at most by a factor . Our results sensibly constrain
theoretical models of X-ray emission from the \psr system.Comment: LATEX, Accepted for publ. in ApJ
Nuclei embedded in an electron gas
The properties of nuclei embedded in an electron gas are studied within the
relativistic mean-field approach. These studies are relevant for nuclear
properties in astrophysical environments such as neutron-star crusts and
supernova explosions. The electron gas is treated as a constant background in
the Wigner-Seitz cell approximation. We investigate the stability of nuclei
with respect to alpha and beta decay. Furthermore, the influence of the
electronic background on spontaneous fission of heavy and superheavy nuclei is
analyzed. We find that the presence of the electrons leads to stabilizing
effects for both decay and spontaneous fission for high electron
densities. Furthermore, the screening effect shifts the proton dripline to more
proton-rich nuclei, and the stability line with respect to beta decay is
shifted to more neutron-rich nuclei. Implications for the creation and survival
of very heavy nuclear systems are discussed.Comment: 35 pages, latex+ep
On the stability of Bose-Fermi mixtures
We consider the stability of a mixture of degenerate Bose and Fermi gases.
Even though the bosons effectively repel each other the mixture can still
collapse provided the Bose and Fermi gases attract each other strongly enough.
For a given number of atoms and the strengths of the interactions between them
we find the geometry of a maximally compact trap that supports the stable
mixture. We compare a simple analytical estimation for the critical axial
frequency of the trap with results based on the numerical solution of
hydrodynamic equations for Bose-Fermi mixture.Comment: 4 pages, 3 figure
Monte Carlo aided design of the inner muon veto detectors for the Double Chooz experiment
The Double Chooz neutrino experiment aims to measure the last unknown
neutrino mixing angle theta_13 using two identical detectors positioned at
sites both near and far from the reactor cores of the Chooz nuclear power
plant. To suppress correlated background induced by cosmic muons in the
detectors, they are protected by veto detector systems. One of these systems is
the inner muon veto. It is an active liquid scintillator based detector and
instrumented with encapsulated photomultiplier tubes. In this paper we describe
the Monte Carlo aided design process of the inner muon veto, that resulted in a
detector configuration with 78 PMTs yielding an efficiency of 99.978 +- 0.004%
for rejecting muon events and an efficiency of >98.98% for rejecting correlated
events induced by muons. A veto detector of this design is currently used at
the far detector site and will be built and incorporated as the muon
identification system at the near site of the Double Chooz experiment
Implications of new measurements of O-16 + p + C-12,13, N-14,15 for the abundances of C, N isotopes at the cosmic ray source
The fragmentation of a 225 MeV/n O-16 beam was investigated at the Bevalac. Preliminary cross sections for mass = 13, 14, 15 fragments are used to constrain the nuclear excitation functions employed in galactic propagation calculations. Comparison to cosmic ray isotonic data at low energies shows that in the cosmic ray source C-13/C approximately 2% and N-14/0=3-6%. No source abundance of N-15 is required with the current experimental results
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
first Autho
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