Parity Nonconservation in Neutron Resonances in 232Th,

Sharon L. Stephenson, Gettysburg College
J D. Bowman, Los Alamos National Laboratory
Bret E. Crawford, Gettysburg College
P P J. Delheij, TRIUMF
C M. Frankle, Los Alamos National Laboratory
M IInuma, Kyoto University
J N. Knudsen, Los Alamos National Laboratory
L Y. Lowie, North Carolina State University
A Masaike, Kyoto University
Y Matsuda, Kyoto University
G E. Mitchell, North Carolina State University
S I. Penttila, Los Alamos National Laboratory
H Postma, Delft University of Technology
N R. Roberson, Duke University
S J. Seestrom, Los Alamos National Laboratory
E I. Sharapov, Joint Institute for Nuclear Research
Y-F Yen, Los Alamos National Laboratory
V W. Yuan, Los Alamos National Laboratory

Copyright held by American Physical Society. First published as SL Stephenson et al, Parity nonconservation in neutron resonances in 232Th, Physical Review C, 58:2, 1236–1246, doi: 10.1103/PhysRevC.58.1236.


Parity nonconservation (PNC) was measured for 24 p-wave resonances from 8 to 300 eV in 232Th by measuring the helicity dependence of the total neutron cross section for epithermal neutrons with an improved experimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all positive, thus confirming the previously observed sign correlation. The data are fit to the sum of two terms, a constant asymmetry and a fluctuating asymmetry. With this ansatz the root-mean-square PNC matrix element M=1.12 meV, which corresponds to a weak spreading widthΓw=4.7×10-7 eV. For the neighboring nuclide 238U there is no constant offset, suggesting that the sign correlation is specific to 232Th.