Faculty Research Publications (Physics)
http://hdl.handle.net/1957/13832
2015-04-27T14:26:52ZNeutron Capture by 94,96Zr and the Decays of 97Zr and 97Nb
http://hdl.handle.net/1957/55579
Neutron Capture by 94,96Zr and the Decays of 97Zr and 97Nb
Krane, K. S.
Cross sections for radiative neutron capture have been determined for ⁹⁴Zr and ⁹⁶Zr using the activation technique with samples of naturally occurring Zr metal. The sensitivity to the correction for epithermal neutrons in the determination of small thermal cross sections is discussed, particularly in view of the variation in the resonance integral at different sites in the reactor. Gamma-ray spectroscopic studies of the decays of ⁹⁷Zr and its daughter ⁹⁷Nb have been performed, leading to improved values of the energies and intensities of the emitted γ rays, and correspondingly improved values for the energy levels and β feedings of excited states populated in ⁹⁷Nb and ⁹⁷Mo.
This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/applied-radiation-and-isotopes/
2014-12-01T00:00:00ZComparing the spectral lag of short and long gamma-ray bursts and its relation with the luminosity
http://hdl.handle.net/1957/55559
Comparing the spectral lag of short and long gamma-ray bursts and its relation with the luminosity
Bernardini, M. G.; Ghirlanda, G.; Campana, S.; Lazzati, D.; et al.
We investigated the rest frame spectral lags of two complete samples of bright long (50)
and short (6) gamma-ray bursts (GRB) detected by Swift. We analysed the Swift/BAT
data through a discrete cross-correlation function (CCF) fitted with an asymmetric
Gaussian function to estimate the lag and the associated uncertainty. We find that
half of the long GRBs have a positive lag and half a lag consistent with zero. All short
GRBs have lags consistent with zero. The distributions of the spectral lags for short
and long GRBs have different average values. Limited by the small number of short
GRBs, we cannot exclude at more than 2 σ significance level that the two distributions
of lags are drawn from the same parent population. If we consider the entire sample
of long GRBs, we do not find evidence for a lag-luminosity correlation, rather the
lag-luminosity plane appears filled on the left hand side, thus suggesting that the lag-luminosity correlation could be a boundary. Short GRBs are consistent with the long
ones in the lag-luminosity plane.
This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Oxford University Press and can be found at: http://mnras.oxfordjournals.org/.
2015-01-11T00:00:00ZFormation and Properties of Astrophysical Carbonaceous Dust. I. Ab-initio Calculations of the Configuration and Binding Energies of Small Carbon Clusters
http://hdl.handle.net/1957/55360
Formation and Properties of Astrophysical Carbonaceous Dust. I. Ab-initio Calculations of the Configuration and Binding Energies of Small Carbon Clusters
Mauney, Christopher; Nardelli, Marco Buongiorno; Lazzati, Davide
The binding energies of n < 100 carbon clusters are calculated using the ab initio density functional theory code
Quantum Espresso. Carbon cluster geometries are determined using several levels of classical techniques and further
refined using density functional theory. The resulting energies are used to compute the work of cluster formation
and the nucleation rate in a saturated, hydrogen-poor carbon gas. Compared to classical calculations that adopt the
capillary approximation, we find that nucleation of carbon clusters is enhanced at low temperatures and depressed
at high temperatures. This difference is ascribed to the different behavior of the critical cluster size. We find that
the critical cluster size is at n = 27 or n = 8 for a broad range of temperatures and saturations, instead of being
a smooth function of such parameters. The results of our calculations can be used to follow carbonaceous cluster/grain formation, stability, and growth in hydrogen-poor environments, such as the inner layers of core-collapse
supernovae and supernova remnants.
This is the publisher’s final pdf. The article is copyrighted by the American Astronomical Society and published by the Institute of Physics Publishing. It can be found at: http://iopscience.iop.org/0004-637X.
2015-02-05T00:00:00ZPhotospheric emission from long duration gamma-ray bursts powered by variable engines
http://hdl.handle.net/1957/55238
Photospheric emission from long duration gamma-ray bursts powered by variable engines
López-Cámara, Diego; Morsony, Brian J.; Lazzati, Davide
We present the results of a set of numerical simulations of long-duration gamma-ray burst
jets aimed at studying the effect of a variable engine on the peak frequency of the photospheric
emission. Our simulations follow the propagation of the jet inside the progenitor star,
its break-out, and the subsequent expansion in the environment out to the photospheric radius.
A constant and two step-function models are considered for the engine luminosity. We show
that our synthetic light-curves follow a luminosity-peak frequency correlation analogous to
the Golenetskii correlation found in long-duration gamma-ray burst observations. Within the
parameter space explored, it appears that the central engine luminosity profile does not have
a significant effect on the location of a gamma-ray burst in the Luminosity-peak frequency
plane, bursts from different central engines being indistinguishable from each other.
This is an author's peer-reviewed final manuscript, as accepted by the publisher. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Oxford University Press on behalf of the Royal Astronomical Society. The published article can be found at: http://mnras.oxfordjournals.org/.
2014-08-11T00:00:00Z