Elastic and inelastic scattering of 1.5-MeV neutrons by the even-A isotopes of zirconium and molybdenum Page: 1,087
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VOLUME 10, NUMBER 3
Elastic and inelastic scattering of 1.5-MeV neutrons by the even-A isotopes of zirconium
F. D. McDaniel,t J. D. Brandenberger, G. P. Glasgow, and H. G. Leighton,
Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506
(Received 31 January 1974)
Differential elastic and inelastic cross sections were measured for 1.5-MeV neutrons scattered by the
even-A isotopes of zirconium and molybdenum. The scattering samples were enriched isotopes of 90Zr,
92Zr, 94Zr, 92MO, 94MO, 96Mo, and 'OMo. The cross sections were measured using a dynamically biased
neutron time-of-flight spectrometer. The differential cross sections have root-mean-square relative and
normalization uncertainties of 2 to 3.5% and 7 to 7.5%, respectively, for elastic scattering, and 6 to
13% and 9 to 15%, respectively, for inelastic scattering. Isotopes with similar level structures have
almost identical elastic angular distributions. The entire set of data was theoretically fitted using the
optical-statistical model with resonance-width-fluctuation corrections. The calculated elastic differential
cross section was assumed to be an incoherent sum of shape-elastic and compound-elastic scattering. At
the minima in the angular distributions the cross sections were dominated by compound-elastic
NUCLEAR REACTIONS 90,92,94Zr, 92'94,96,t100Mo(n, n), (n n'), En=1.5 MeV;
measured o(0); deduced optical model parameters. Isotopically enriched
samples, neutron time of flight, dynamic bias, compound-elastic scattering,
level width fluctuations.
An extensive study of neutron elastic and inelas-
tic scattering in the mass A = 90 region is in prog-
ress at this laboratory.1-12 Data have been taken
over a period of several years to study neutron
scattering and scattering mechanisms in the inci-
dent neutron energy range of 1.5 to 8.6 MeV. The
study encompasses five even-A isotopes of Mo and
three even-A isotopes of Zr, Mo with A = 92 to
100 and Zr with A = 90 to 94. The entire set of
cross sections, both elastic and inelastic, is now
in the process of being analyzed with a consistent
set of optical model parameters. This paper re-
ports the study of elastic and inelastic scattering
of 1.5 MeV neutrons by seven nuclei in the mass
region A = 90 to 100: 9Zr, 92Zr, 9Zr, 92Mo, "Mo,
96Mo, Mo. A lower limit of 1.5 MeV was chosen
for the study because Lambropoulos et al.13 have
made an extensive set of cross section measure-
ments for the Mo isotopes and for natural molyb-
denum from 0.1 to 1.5 MeV.13, 14
11. EXPERIMENTAL APPARATUS
The neutron differential cross sections were
measured using a dynamically biased neutron time-
of-flight (TOF) spectrometer.15-17 The dynamically
biased neutron TOF spectrometer was developed
at the University of Kentucky as a means for re-
ducing the high backgrounds typically associated
with neutron scattering experiments.
The University of Kentucky Model CN Van de
Graaff accelerator was used to produce mono-
energetic neutrons using the T(p, n)3He reaction.
For the TOF experiments the accelerator beam
was terminally pulsed at 2.0 MHz and had a pulse
width of less than 10 nsec. The beam pulse width
was further shortened to less than 1.0 nsec by a
Mobley beam pulse compression system.l20 The
beam, collimated by a 0.48 cm aperture, was
passed through a 0.000 36 cm Mo foil into a tritium
gas cell. The cylindrical gas cell was made of
thin walled stainless steel 0.8 cm in diameter and
3.0 cm in length and was lined with tantalum 0.025
cm thick. The tritium gas pressure was main-
tained at a pressure of 1.0 atm. The proton energy
loss in passing through the Mo foil and the 3.0 cm
of 3H gas was 231 keV and 83 keV, respectively.
The neutron energy produced at 00 at the center
of the gas cell was 1.5 MeV. The total spread in
neutron energy was 84 keV.
The experimental arrangement is shown in Fig.
1. The massive detector shield, mounted on a
goniometer, is used to reduce the room-scattered
background, the neutrons striking the detector
directly from the source, and other accelerator
associated backgrounds. Two neutron detectors
were used in these measurements since the ex-
periments for Mo and Zr were done at different
times because of the limited availability of the iso-
topically enriched samples. Both detectors were
NE 218 liquid organic scintillators, 10.0 cm in
PHYSICAL REVIEW C
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McDaniel, Floyd Del. (Floyd Delbert), 1942-; Brandenberger, J. D.; Leighton, H. G. & Glasgow, G. P. Elastic and inelastic scattering of 1.5-MeV neutrons by the even-A isotopes of zirconium and molybdenum, article, September 1974; [College Park, Maryland]. (digital.library.unt.edu/ark:/67531/metadc146595/m1/1/: accessed December 16, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.