Program - Brookhaven National Laboratory

Facility (HRIBF) at Oak Ridge National Laboratory. Total absorption spectroscopy of fission products is
important for the verification and development of nuclear structure models, as well as for the determination
of decay heat released by radioactive nuclei during nuclear fuel cycle. The MTAS detector array consists of
19 NaI(Tl) hexagonal shape detectors, each one is 21 inches long and about 8 inches maximum diameter.
MTAS is mounted on a movable cart allowing to adjust the height. The entire MTAS array is surrounded by
over 12,000 pounds of lead and paraffin shielding. This heavy shielding consists of three individual movable
segments. MTAS efficiency for full energy deposition of a single gamma ray approaches nearly 93% around
300 keV and it is about 68% for a 5 MeV gamma-transition. The energy resolution of individual MTAS
modules is below 6% at 1.33 MeV and about 7% to 8% at 0.66 MeV. Auxiliary detectors include two
segmented 1-mm-thick silicon strip detectors placed inside the MTAS array around the tape transporting
collected activities. These Si-counters cover over 80% of the solid angle for beta-energy loss detection
and help to center the radioactive samples inside MTAS. The energy resolution for 976 keV electrons is
about 2.5% (∼25 keV) and the low energy threshold for electrons is less then 50 keV. The on-line MTAS
commissioning run was performed in January 2012 at the mass separator on-line to the HRIBF Tandem
accelerator. Over twenty decays of fission products have been studied using MTAS including seven decays
defined as having the highest priority for decay heat analysis in nuclear reactor by the assessment of OECD
Nuclear Energy Agency. Selected results will be presented at this meeting [1]. *This work was supported
by the U.S. Department of Energy Office of Nuclear Physics.
[1] M. Karny et al., “First results from the Modular Total Absorption Spectrometer at the HRIBF (ORNL,
Oak Ridge),” ND2013 Proceedings.
HF 3 4:20 PM
Measurements of the (n, 2n) Reaction Cross Section of 181 Ta from 8 MeV to 14.5 MeV
C. Bhatia, W. Tornow
TUNL,Duke University,Durham, North Carolina 27708, USA
M.E. Gooden
TUNL, North Carolina State University, Raleigh, North Carolina 27695, USA
A. Tonchev
Lawrence Livermore National Laboratory, Livermore, California 94550, USA
Nuclear data are the backbone of nuclear technology. They are useful in many areas such as design and
modeling of nuclear energy systems,radiation safety, activation techniques, and interdisciplinary areas like
production of radioisotopes for medical and industrial applications, space applications, radiation damage
studies, environmental monitoring, etc. In addition, precise nuclear data, particularly cross-section measurements
are playing an important role in fundamental research, to test different statistical-model codes
and to provide insight into the reaction mechanisms in different energy regimes. 180 Ta is a subject of
extensive study in nuclear physics. It is a natural isomeric target, and therefore of great interest for nuclear
astrophysics as well. Furthermore, the 181 Ta(n, 2n) 180 Ta reaction was used as witness foils (chemical
tracers) in underground tests of nuclear devices to assess their performance and very recently, also for diagnostic
purposes at NIF (National Ignition Facility). The cross section of the reactions 181 Ta(n, 2n) 180 Ta
was measured from 8 to 14.5 MeV in small energy steps to resolve inconsistencies in the existing database.
For the first time the cross section of the (n, 2n) reaction on 181 Ta was measured for neutron energies
near threshold. Mono-energetic neutron beams were produced via the 2 H(d, n) 3 He reaction, known for
its high neutron yield in the energy region of the present measurements. The induced γ-ray activity of
180 Ta was measured with high-resolution HPGe detectors. The acquired γ-ray spectra, from the off-line
measurements of the activated samples, were analyzed to identify the reaction products and to determine
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