Program - Brookhaven National Laboratory

ND 4 11:40 AM
New Beta-Delayed Neutron Measurements in the Light-Mass Fission Group
J. Agramunt, A. Algora, C. Domingo, B. Rubio, J.L. Tain, E. Valencia, Instituto de Física Corpuscular,
CSIC-Univ. Valencia, Valencia, Spain. M.B. Gomez Hornillos, R. Caballero, F. Calvino, G. Cortes, A.
Riego, Universitat Politécnica de Catalunya, Barcelona, Spain. A. Garcia, D. Cano-Ott, T. Martinez,
CIEMAT, Madrid, Spain. P.J. Mason, Z. Podolyak, University of Surrey, Guilford, UK. J. Rissanen, J.
Aysto, T. Eronen, A. Jokinen, A. Kankainen, I. Moore, H. Penttilä, University of Jyväskylä, Jyväskyä,
Finland.
The phenomenon of beta-delayed neutron emission is of fundamental importance in the operation and
control of power reactors. Although quantitatively small, the delayed neutron fraction modulates effectively
the changes of reactor power to sudden changes of the reactivity. The total number of delayed neutrons
per fission νd can be obtained from summation calculations based on fission yields Y and neutron emission
probabilities Pn. An improvement of the accuracy of such calculations requires an improvement in the
knowledge of both experimental quantities [1]. In particular for Gen IV reactors with a high content
on minor actinides the fission product distribution could be quite different from conventional reactors. A
sensitivity study was performed at both thermal and fast neutron energies and for major an minor actinides
to determine which fission products contributing significantly to νd should be revisited experimentally in
view of the current uncertainties. Following this study a measurement of Pn values has been carried out at
the chemically insensitive IGISOL mass separator installed at the University of Jyväskylä (JYFL) with the
BELEN 4π neutron counter [2]. Furthermore aiming at an improved accuracy of the measurements, the
JYFLTRAP Penning trap was coupled to the separator in order to produce isotopically pure radioactive
beams of the species under study. In this first measurement the selection of nuclei was further constrained
by their interest in astrophysics and nuclear structure studies. During the astrophysical rapid (r) neutron
capture process an initial distribution of very neutron rich isotopes is produced in a very short time,
which afterwards decay back to stability. This initial abundance distribution is altered by the delayed
neutron emission process, which shifts the β-decay flow to lower masses and provides an additional source
of neutrons for late captures. The nuclei finally selected are relatively close to the r-process path and
above 78 Ni, influencing the first r-abundance peak. The measured Pn will provide also information about
the fraction of the β-strength distribution Sβ lying above the neutron separation energy Sn which can be
compared with theoretical calculations. The preliminary results of the analysis of this experiment together
with the implications will be presented.
Corresponding author: J. L. Tain
[1] A. D’Angelo, Prog. Nucl. Ener. 41 (2002) 5. [2] M.B. Gomez-Hornillos et al., J. Phys. Conf. Ser. 312
(2011) 052008
Session NE Benchmark and Testing
Thursday March 7, 2013
Room: Central Park West at 10:30 AM
NE 1 10:30 AM
TENDL-2012 Processing, Verification and Validation Steps
Jean-Christophe Sublet
UK Atomic Energy Authority, Culham Science Centre, Abingdon OX14 3DB, United Kingdom
197