Program - Brookhaven National Laboratory

a lower nuclear temperature than the light one. As a result the excitation energy is transferred from
the light to the heavy fragment, resulting in higher neutron emission. Up to date, the correct neutron
emission model is still under debate. It is a crucial link in our understanding of the fission process as
well as for established evaluated data files. Therefore, it is of importance to study the impact on fission
observables, when applying either of the two neutron evaporation models. In this work we investigated the
consequences of the two different models on the fission-fragment distributions from the reaction 234 U(n, f).
The measurements were performed by means of a double Frisch-grid ionization-chamber at the MONNET
neutron source of the Joint Research Centre IRMM. We found that the choice of neutron-emission correction
has a strong impact on the mass and energy distributions. The effect of neutron correction seems to affect
mainly the post-neutron distribution, therefore, motivating new experiments dedicated to the measurement
of prompt-fission neutrons in coincidence with fragment properties.
[1] A.A. Naqvi, F. Käppeler, F. Dickmann and R. Müller, Phys. Rev. C 34 (1986) 218-225. [2] R. Müller,
A.A. Naqvi, F. Käppeler, F. Dickmann, Phys. Rev. C 29 (1984) 885-905. [3] K.-H. Schmidt and B. Jurado,
Phys. Rev. Lett. 104, 212501 (2010). [4] K.-H. Schmidt and B. Jurado, Phys. Rev. C 83:061601 (2011).
[5] C. Manailescu, A. Tudora, F.-J. Hambsch, C. Morariu and S. Oberstedt. Nucl. Phys. A867 1 (2011)
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DF 4 4:40 PM
Measurements of Neutron Cross Sections for Chromium, Yttrium and Terbium at 197 MeV
H. Suzuki, Kyoto University Research Reactor Institute. S. Sekimoto, Kyoto University Research Reactor
Institute. H. Yashima, Kyoto University Research Reactor Institute. K. Ninomiya, Graduate School of
Science, Osaka University. Y. Kasamatsu, Graduate School of Science, Osaka University. T. Shima,
Research Center for Nuclear Physics, Osaka University. N. Takahashi, Graduate School of Science, Osaka
University. A. Shinohara, Research Center for Nuclear Physics, Osaka University. H. Matsumura, High
Energy Accelerator Research Organization. M. Hagiwara, High Energy Accelerator Research Organization.
K. Nishiizumi, Space Sciences Laboratory, University of California, Berkeley. M. W. Caffee, Department
of Physics, Purdue University. S. Shibata, Kyoto University Research Reactor Institute.
Neutron-induced reaction cross sections are essential to cosmochemists aiming to decipher the cosmic-ray
irradiation history. These cross section data also serve as a comprehensive nuclear database for estimating
residual radioactivities in accelerator facilities. Neutron cross sections in the energy range above 100 MeV
have scarcely been measured experimentally; exceptions are for the target materials C, Cu, Pb, Bi and a
few others. In many instances the neutron cross section is based on the corresponding proton cross section,
the assumption being that above 100 MeV they are similar. Cross sections also can be calculated from
physic-based codes. In this work, we measured reaction cross sections of radionuclides produced through
nuclear spallation reactions from Cr, Y and Tb induced by neutrons at 197 MeV; our experiments are the
first to report these cross sections. The irradiations were carried out using neutrons produced through
Li-7 (p,n) reaction at N0 beam line in the Research Center for Nuclear Physics (RCNP), Osaka University.
To estimate quasi-monoenergetic neutron induced cross sections, the target stacks of Cr, Y and Tb were
irradiated on the two angles of 0 and 25 degrees for the axis of the primary proton beam. The yields of
the spallation products were measured by gamma-ray spectrometry. Neutron cross sections were estimated
by subtracting the yields produced in the samples placed on 25 degree from those of 0 degree to correct
the contribution of the low energy tail in the neutron spectrum. The results obtained in this work will be
compared to the cross section data for the same target materials with 287 and 386 MeV neutrons in our
previous work. We will also compare neutron cross sections obtained to those from calculation codes.
Corresponding author: S. Sekimoto
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