Program - Brookhaven National Laboratory

to librarian covariances. The energy range ∼100-200 keV is also extremely important in the description
of fast neutron systems (e.g. for fast Generation-IV reactors). The MACS of the different elements can
be measured directly by activation providing a maxwellian neutron spectrum at the sample position. Beer
and Käppeler [1] is considered the classical work in this field, they showed the possibility to produce a
quasi maxwellian neutron spectra at kT=25 keV by the Li-7(p,n) reaction at proton energy near-threshold.
Then the MACS at the reference temperature (30 keV) can be obtained by a correction of the spectrum
and an extrapolation from 25 to 30 keV. Mastinu et al [2] proposed a new method for producing maxwellian
neutron spectra at different temperatures [3], in particular a very accurate maxwellian spectrum at kT=30
keV can be achieved. While the classical method uses monochromatic proton energy, the key point of the
Mastinu et al method is to shape the proton beam to a particular distribution near-threshold the Li-7(p,n)
reaction by means of an energy degrader that can be made of different material and thicknesses. The
Mastinu et al method is used to measure by activation the MACS of the Tm169(n,g) reaction at kT=30
keV using Au-197(n,g) as a reference. The available experimental data for this reaction is rather limited
and there is only one available data for the MACS at kT=30 keV obtained by the TOF technique [4]. The
method will be explained and the results will be shown. Around 13% of the solar abundance of Thulium is
made by the slow neutron capture process. Astrophysical implications will be discussed for nucleosynthesis
in stars driven by s-process.
[1] H. Beer and F. Käppeler, Phys. Rev. C 21, 534 (1980). [2] P. F. Mastinu, G. Martin-Hernandez,
and J. Praena, A method to obtain a Maxwell-Boltzmann neutron spectrum at kT=30 keV for nuclear
astrophysics studies, Nucl. Inst. and Met. in Phys. Res. A 601, 333 (2009). [3] J. Praena et al, Medida de
secciòn eficaz estelar Ta(n,g) en el CNA, XXXIII Reuniòn Bienal de la Real Sociedad Española de Fisica
207, ISBN: 978-84-86116-40-8. [4] R. Macklin, Nucl. Sci. Eng. 82, 143 (1982).
LB 6 5:15 PM
Beta Decay in The Region Of Neutron-Deficient 69,70,71 Kr
A.M. Rogers, C.J. Lister, J.A. Clark, S.M. Fischer, E.A. McCutchan, G. Savard, D. Seweryniak
Physics Division, Argonne National Laboratory, Argonne, IL 60439 USA
A.M. Rogers
Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA
J. Giovinazzo, B. Blank, G. Canchel
Centre d’Etudes Nucleaires de Bordeaux-Gradignan, Universite Bordeaux 1, UMR 5797 CNRS/IN2P3,
Chemin du Solarium, BP 120, F-33175, Gardignan Cedex, France
G. de France, S. Grevy, F. de Oliveira Santos, I. Stefan, J.-C. Thomas
GANIL CEA/DSM-CNRS/IN2P3, Boulevard Henri Becquerel, BP55027, 14076 CEAN Cedex 5, France
Proton-rich nuclei beyond the N = Z line play a key role in our understanding of astrophysics, weakinteraction
physics, and nuclear structure. The decay of 69 Kr (Tz = −3/2) is of particular interest as
it populates states in the proton-unbound nucleus 69 Br, critical to the rapid proton-capture (rp) process
thought to power type I x-ray bursts. During the astrophysical rp process, 2p-capture reactions through
69 Br can bypass the “waiting-point” nucleus 68 Se [1]. The bypass-reaction rate depends strongly on the
proton-capture Q value. A β-decay experiment was conducted at GANIL which utilized implant-β-proton
and β-γ correlations to study nuclear structure and decay properties primarily related to the β decays of
69,70,71 Kr. Neutron-deficient isotopes ranging from Zn to Kr were implanted into a Si-DSSD detector located
at the focal plane of the LISE spectrometer in which spatially and temporally correlated implantation and
decay events were studied. Gamma rays were detected in surrounding EXOGAM high-purity germanium
clover detectors. We measured β-decay half lives for 69,70,71 Kr of 27(3) ms, 40(6) ms, and 92(9) ms,
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