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Title: Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission

Abstract

In this study, the NPDGamma collaboration is performing a measurement of the very small parity-violating asymmetry in the angular distribution of the 2.2 MeV γ-rays from the capture of polarized cold neutrons on protons (A γ). The estimated size of A γ is 5×10 -8, and the measured asymmetry is proportional to the neutron polarization upon capture. Since the interaction of polarized neutrons with one of the two hydrogen molecular states (orthohydrogen) can lead to neutron spin-flip scattering, it is essential that the hydrogen in the target is mostly in the molecular state that will not depolarize the neutrons (≥99.8% parahydrogen). For that purpose, in the first stage of the NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE), we operated a 16-l liquid hydrogen target, which was filled in two different occasions. The parahydrogen fraction in the target was accurately determined in situ by relative neutron transmission measurements. The result of these measurements indicate that the fraction of parahydrogen in equilibrium was 0.9998±0.0002 in the first data taking run and 0.9956±0.0002 in the second. We describe the parahydrogen monitor system, relevant aspects of the hydrogen target, and the procedure to determine the fraction of parahydrogen in the target.more » In addition, assuming thermal equilibrium of the target, we extract the scattering cross-section for neutrons on parahydrogen.« less

Authors:
 [1]
  1. Arizona State Univ., Tempe, AZ (United States).et al
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1265347
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
Additional Journal Information:
Journal Volume: 659; Journal Issue: 1; Journal ID: ISSN 0168-9002
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Barro´ n-Palos, L. Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission. United States: N. p., 2011. Web. doi:10.1016/j.nima.2011.07.051.
Barro´ n-Palos, L. Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission. United States. https://doi.org/10.1016/j.nima.2011.07.051
Barro´ n-Palos, L. Sat . "Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission". United States. https://doi.org/10.1016/j.nima.2011.07.051.
@article{osti_1265347,
title = {Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission},
author = {Barro´ n-Palos, L.},
abstractNote = {In this study, the NPDGamma collaboration is performing a measurement of the very small parity-violating asymmetry in the angular distribution of the 2.2 MeV γ-rays from the capture of polarized cold neutrons on protons (Aγ). The estimated size of Aγ is 5×10-8, and the measured asymmetry is proportional to the neutron polarization upon capture. Since the interaction of polarized neutrons with one of the two hydrogen molecular states (orthohydrogen) can lead to neutron spin-flip scattering, it is essential that the hydrogen in the target is mostly in the molecular state that will not depolarize the neutrons (≥99.8% parahydrogen). For that purpose, in the first stage of the NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE), we operated a 16-l liquid hydrogen target, which was filled in two different occasions. The parahydrogen fraction in the target was accurately determined in situ by relative neutron transmission measurements. The result of these measurements indicate that the fraction of parahydrogen in equilibrium was 0.9998±0.0002 in the first data taking run and 0.9956±0.0002 in the second. We describe the parahydrogen monitor system, relevant aspects of the hydrogen target, and the procedure to determine the fraction of parahydrogen in the target. In addition, assuming thermal equilibrium of the target, we extract the scattering cross-section for neutrons on parahydrogen.},
doi = {10.1016/j.nima.2011.07.051},
url = {https://www.osti.gov/biblio/1265347}, journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
issn = {0168-9002},
number = 1,
volume = 659,
place = {United States},
year = {2011},
month = {1}
}