Systematic error in the precision measurement of the mean wavelength of a nearly monochromatic neutron beam due to geometric errors

Published

December 3, 2009

Author(s)

Kevin J. Coakley, Maynard S. Dewey, Andrew T. Yue, Alexander Laptev

Abstract

Many experiments at neutron scattering facilities require nearly monochromatic neutron beams. In such experiments, one must accurately measure the mean wavelength of the beam. We seek to reduce the systematic uncertainty of this measurement to approximately 0.1 percent. This work is mainly motivated by an effort to improve the measurement of the neutron lifetime determined from data collected in a 2003 in-beam experiment performed at NIST. More specifically, we seek to reduce systematic uncertainty by calibrating the neutron detector used in this lifetime experiment. This calibration requires simultaneous measurement of the responses of both the neutron detector used in the lifetime experiment and an absolute black neutron detector to a highly collimated nearly monochromatic beam of cold neutrons, as well as a separate measurement of the mean wavelength of the neutron beam. The calibration uncertainty will depend on the uncertainty of the measured efficiency of the black neutron detector and the uncertainty of the measured mean wavelength. The mean wavelength of the beam is measured by Bragg diffracting the beam from a nearly perfect silicon analyzer crystal. Given the rocking curve data and knowledge of the directions of the rocking axis and normal to the scattering planes in the silicon crystal, one determines the mean wavelength of the beam. In practice, the direction of the rocking axis and the normal to the silicon scattering planes are not known exactly. Based on Monte Carlo simulation studies, we quantify systematic uncertainties in the mean wavelength measurement due to these geometric errors. Both theoretical and empirical results are presented and compared.

Proceedings Title

Proceedings of the International Workshop on Particle Physics with Slow Neutrons, May 29-31, 2008. Institut Laue Langevin, Grenoble, France.

Volume

A 611

Conference Dates

May 29-31, 2008

Conference Location

Grenoble

Pub Type

Conferences

Keywords

Lifetimes, Neutron physics, Neutron scattering, Nuclear tests of fundamental interactions and symmetries, Properties of protons and neutrons, Probability theory, stochastic processes, and statistics.

Citation

Coakley, K. , Dewey, M. , Yue, A. and Laptev, A. (2009), Systematic error in the precision measurement of the mean wavelength of a nearly monochromatic neutron beam due to geometric errors, Proceedings of the International Workshop on Particle Physics with Slow Neutrons, May 29-31, 2008. Institut Laue Langevin, Grenoble, France. , Grenoble, -1 (Accessed October 7, 2025)