Speaker
Hisham Nassar
(Hebrew University, Jerusalem, Israel 91904)
Description
The 44Ti(t1/2= 59 y) nuclide is considered an important signature of
core-collapse supernova (SN) nucleosynthesis and has recently been
observed as live radioactivity by gamma-ray astronomy from the Cas A
SN remnant. We investigated in the laboratory the major 44Ti production
reaction, 40Ca(alpha,gamma)44Ti (Ecm ~0.6-1.2 MeV/u), by off-line
counting of 44Ti nuclei using accelerator mass spectrometry [1]. The
observed yield is significantly higher than inferred from previous
prompt-gamma spectroscopy experiments. The present data strongly
support the BRUSLIB statistical model [2] which incorporates a
microscopic model of nuclear level densities and of the gamma-ray
strength function, and a global alpha-nucleus optical-model potential.
Comparison of the data with the statistical model confirms the strong
suppression in yield expected for (alpha,gamma) reactions on
self-conjugate (N=Z) nuclei. The derived astrophysical rate of the
40Ca(alpha,gamma)44Ti reaction is a factor 5-10 higher than calculated
in current models. We will present results of stellar calculations in
spherical hydrodynamics, as those described in [3] but using this
reaction rate, showing an increase of the calculated SN 44Ti yield by
a factor ~2 over current estimates. An increase by a factor of ~2 in
44Ti is found also in the calculated fall back material. The yields
calculated by multi-dimensional SN explosion calculations proposed to
explain the observed 44Ti yield of Cas A, in which parts of deeper
layers can be ejected while some of the outer layers fall back, are
expected to be enhanced in 44Ti as well. This work was supported in
part by the US- DOE, Office of Nuclear Physics, under Contract
No. W-31-109-ENG-38, the DOE Program for Scientific Discovery through
Advanced Computing (SciDAC; DE-FC02-01ER41176), by DOE contract
W-7405-ENG-36 to the Los Alamos National Laboratory, and by the
USA-Israel Binational Science Foundation (BSF).
[1] H. Nassar et al., Phys. Rev. Lett., to be published.
[2] M.Arnould and S.Goriely, Nucl. Phys. A, to be published.
[3] T.Rauscher et al., Astrophys. J., 576, 323 (2002).
Authors
Hisham Nassar
(Hebrew University, Jerusalem, Israel 91904)
Prof.
Michael Paul
(Hebrew University, Jerusalem, Israel 91904)
Co-authors
Dr
Alexander Heger
(Los Alamos National Laboratory, NM 87545, USA)
Mr
Avishai Ofan
(Hebrew University, Jerusalem, Israel 91904)
Dr
Guy Savard
(Argonne National Laboratory, Illinois 60439)
Dr
K. Ernst Rehm
(Argonne National Laboratory, Illinois 60439)
Prof.
Michael Hass
(Weizmann Institute, Rehovot, Israel 76100)
Dr
Richard Pardo
(Argonne National Laboratory, Illinois 60439)
Dr
Richard Vondrasek
(Argonne National Laboratory, Illinois 60439)
Dr
Robert V.F. Janssens
(Argonne National Laboratory, Illinois 60439)
Prof.
Stephane Goriely
(Universite Libre de Bruxelles, 1050 Brussels, Belgium)
Dr
Yoav Kashiv
(Hebrew University, Jerusalem, Israel 91904)
