JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
19. Measurement of Resonance Parameters of 155,156,157,158,160 Gd by using pulsed
neutrons with energy ranges from 10 eV to 1 keV
Yeong-Rok Kang*, Tae-Ik Ro
Department of Physics, Dong-A University, Busan 604-714, Korea
Email: tiro@donga.ac.kr
Guinyun Kim, Manwoo Lee
Department of Physics, Kyungpook National University, Daegu 702-701, Korea
Y. Danon, M.J Rapp, D. Williams
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute
Troy, New York 12180-3590
G. Leinweber, D.P Barry, R.C. Block
Bechtel Marine Propulsion Corporation, Knolls Atomic Power Laboratory
P.O. Box 1072, Schenectady, New York 12301-1072
We explored neutron interactions with Gadolinium isotopes in the energy region from 10 eV to 1 keV
at the electron linear accelerator facility at the Rensselaer Polytechnic Institute (RPI). The neutron capture
measurements were made at a flight path of 25 m with a 16-segment sodium iodide multiplicity detector by
using the time-of-flight technique. Five high-purity gadolinium isotopes ( 155 Gd, 156 Gd, 157 Gd, 158 Gd, and 160 Gd)
and two natural gadolinium samples were used for the neutron capture measurement. Resonance parameters for
155,156,157,158,160
Gd were obtained by using the multilevel R-matrix Bayesian code SAMMY. The samples are
placed in the center of a cylindrical 16-segment thallium activated sodium iodide NaI(Tl) detector. Each NaI(Tl)
piece is pie shaped and optically separated from each other. All of the NaI(Tl) pieces are housed within an
aluminum can with photomultipliers attached to each pie shaped segment. Many new resonances of the
epithermal region are proposed, and other resonances previously identified in the literature have been revised.
The poor match of the ENDF/B-VII.0 parameters to the current data is significant, and substantial improvement
to the understanding of gadolinium cross sections is presented, particularly above 180.4 eV where the ENDF/B-
VII.0 resolved region for 155 Gd ends. As a result, fitting data above 180.4 eV was performed without initial
estimates for resonance locations and widths as a challenging task. Also new fitting result of 157 Gd above
306.4eV of the upper limit of ENDF/B-VII.0 was presented.
1. Introduction
The neutron capture cross-sections of gadolinium (Gd) isotopes are important in the design of reactors, as
well as in nuclear-reaction and astrophysical studies. Since the major portion of the natural Gd capture crosssections
is due to 155 Gd and 157 Gd, an accurate knowledge of the cross-sections for those isotopes is also of
importance to calculate the reactor characteristics when Gd is used as a burnable poison in light water reactors.
The purpose of the present work was to measure the neutron capture cross-sections and to determine resonance
parameters for Gd isotopes that are an improvement over the current gadolinium evaluations. In addition, the
data are important for examining the availability of Gd as a control material for fast reactors. 1
In the region from 1.0 to 300.0 eV, most of the resonances occur in 155 Gd and 157 Gd. In these two isotopes,