Parity violation in 232Th neutron resonances above 250 eV

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
J E. Lynch, Gettysburg College
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 EI Sharapov et al, Parity violation in 232Th neutron resonances above 250 eV, Physical Review C, 61, 025501, doi: 10.1103/PhysRevC.61.025501.


The analysis of parity nonconservation (PNC) measurements performed on 232Th by the TRIPLE Collaboration has been extended to include the neutron energy range of 250 to 1900 eV. Below 250 eV all ten statistically significant parity violations have the same sign. However, at higher energies PNC effects of both signs were observed in the transmission of longitudinally polarized neutrons through a thick thorium target. Although the limited experimental energy resolution precluded analysis in terms of the longitudinal asymmetry, parity violations were observed and the cross section differences for positive and negative neutron helicities were obtained. For comparison, a similar analysis was performed on the data below 250 eV, for which longitudinal asymmetries were obtained previously. For energies below 250 eV, the p-wave neutron strength functions for the J=1/2 and J=3/2 states were extracted: S1/21=(1.68±0.61)×10-4 and S3/21=(0.75±0.18)×10-4. The data provide constraints on the properties of local doorway states proposed to explain the PNC sign effect in thorium.