43 research outputs found
Reaction rate for two--neutron capture by He
Recent investigations suggest that the neutrino--heated hot bubble between
the nascent neutron star and the overlying stellar mantle of a type--II
supernova may be the site of the r--process. In the preceding --process
building up the elements to , the He(2n,)He--
and He(,n)Be--reactions bridging the instability gap at
and could be of relevance. We suggest a mechanism for
He(2n,)He and calculate the reaction rate within the
+n+n approach. The value obtained is about a factor 1.6 smaller than
the one obtained recently in the simpler direct--capture model, but is at least
three order of magnitude enhanced compared to the previously adopted value. Our
calculation confirms the result of the direct--capture calculation that under
representative conditions in the --process the reaction path proceeding
through He is negligible compared to He(n,)Be.Comment: 13 pages, 4 postscript figures, to appear in "Zeitschrift f. Physik
A", changed internet address and filename, the uuencoded postscript file
including the figures is available at
ftp://is1.kph.tuwien.ac.at/pub/ohu/twoneutron.u
Nuclear Level Density and the Determination of Thermonuclear Rates for Astrophysics
The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. We discuss the model mostly employed for
such calculations: the statistical model (Hauser-Feshbach). Special emphasis is
put on the uncertainties arising from nuclear level density descriptions and an
improved global description is presented. Furthermore, criteria for the
applicability of the statistical model are investigated and a "map" for the
applicability of the model to reactions of stable and unstable nuclei with
neutral and charged particles is given.Comment: REVTeX paper + 7 B/W figures + 2 color figures; PRC, in press. Also
available at http://quasar.physik.unibas.ch/preps.htm
New filovirus disease classification and nomenclature
Filoviruses, the members of the family Filoviridae, are
currently classified into one proposed and five established
genera (Supplementary Table 1). Of the twelve
described filoviruses, six have been identified as aetiological
agents of naturally occurring human disease
outbreaks