Review of Livermore-Led Neutron Capture Studies Using DANCE Page: 4 of 6
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International Conference on Nuclear Data for Science and Technology 2007
The 157,160Gd materials were very pure, while the 1'54Gd
targets were less pure. However the 1' 4Gd isotopes are
significantly enriched above the natural abundance. We also
made and measured a natGd target. A summary of the target
materials is given in Table 1. In each case, the gadolinium
material was electroplated onto 0.5 mil beryllium foils.
The 242mAm material was made by irradiation of 24 Am in the
Idaho National Laboratory's reactor. Samples were recently
purified and electroplated onto 0.5 mil beryllium foils. The
total target mass for our initial measurement was about 47 [ug
Table 1. Isotopic compositions, in percent, of the five Gd targets.
The 157'160Gd materials are very pure.
Isotope natGd 12Gd 14Gd "5Gd 160Gd
152Gd 0.20 42.49 0.05 <0.01 <0.01
4Gd 2.18 4.38 67.34 <0.01 0.02
155Gd 14.80 15.93 21.11 0.09 0.22
156Gd 20.46 13.91 5.65 0.09 0.37
157Gd 15.65 7.82 2.24 99.7 0.27
158Gd 24.84 9.56 2.32 0.12 0.92
160Gd 21.87 5.91 1.29 <0.01 98.2
3 Data Analysis and Experimental Results
The 94'95Mo(n,y) reactions were studied for neutron energies
from thermal to 16 keV. The primary motivation for these
measurements was to test an enhancement observed in the
low energy behavior of the photon strength function in
98Mo by the Oslo Cyclotron group.3
Gamma-ray distribution and average y cascade multiplicities
were measured following resonant neutron capture. These
spectra were compared with simulations, which were
performed with DICEBOX4 and GEANT4. The DICEBOX
output was the input for GEANT4. Models of the photon
strength function with an Oslo-type enhancement below 1
MeV were unable to reproduce experimental spectra.
However, good agreement was found between DANCE
spectra and simulations that postulate a low-lying resonance
in the photon strength function; this is intermediate in
strength between the KMF model and an Oslo-type photon
New spin assignments were made for resonances in the
,96Mo excited nuclei. Assignments were made using the
multiplicity of the y-ray cascades and the y-ray spectral
shape. In the 96Mo compound nucleus, 56 new resonances
were observed. Seventeen resonances were given a new spin
assignment, and 22 resonances were given a tentative spin
assignment. For the 95Mo compound nucleus, 39 resonances
were observed, and 21 resonances were given a parity
With the new resonance information, the resonance spacing
can be improved. The new spacing, Do, is 82 eV, a change of
more than 20% from 105 + 10 eV in the Reference Input
Parameter Library. The change in resonance spacing results
in a cross-section change of as much as 40%.
The 1si,1s3Eu(n,y) reactions were studied because there was a
large (30-40%) difference between the existing data sets.57
The historical data is shown in Fig. 1. All measurements
shown in Fig. 1 were made with C6D6 detectors. The
evaluated cross-section set is currently an average of these
Fig. 1. Three measurements of 151Eu(n,y) taken in 1977, 1979, and
1987. These measurements have a 30-40% difference between
New 1si,1s3Eu measurements were made using the DANCE
array. The instrumental y-ray multiplicity of the detector
array was utilized for the background subtraction, using the
observation that events from the neutron capture of the
isiis3Eu targets are dominantly of multiplicity 3 and 4, while
events due to background are of low multiplicity." Results
suggest that we should reduce the evaluated cross section for
incident neutrons above 1 keV. The entire neutron energy
range is shown in Fig. 2, and the energy range from 0.1 keV
to 100 keV is shown in Fig. 3.
For 151Eu, the cross section was normalized to the well-
known doublet at 0.3 - 0.4 eV measured by Widder, et al.9
Similarly, the 1s3Eu cross section (not shown) was
normalized to the values determined by Widder. In Figs. 2
and 3, we also include data by Best, et al.,10 which appears to
agree with the Kononov data.
o Yzamoto 79
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Parker, W; Sheets, S; Agvaanluvsan, U; Becker, J; Becvar, F; Bredeweg, T et al. Review of Livermore-Led Neutron Capture Studies Using DANCE, article, May 11, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc880800/m1/4/: accessed November 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.