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Title: Measuring Neutron Spectrum at MIT Research Reactor Utilizing He-3 Bonner Cylinder Approach with an Unfolding Analysis

Abstract

The Ricochet experiment seeks to measure Coherent (neutral-current) Elastic Neutrino-Nucleus Scattering using dark-matter-style detectors with sub-keV thresholds placed near a neutrino source, such as the MIT (research) Reactor (MITR), which operates at 5.5 MW generating approximately 2.2e18 neutrinos/second at the core. Currently, Ricochet is characterizing the backgrounds at MITR, the main component of which comes in the form of neutrons emitted from the core simultaneous with the neutrino signal. To characterize this background, we wrapped a Bonner cylinder around a He-3 thermal neutron detector, whose data was then unfolded to produce a neutron energy spectrum across several orders of magnitude. We discuss the resulting spectrum and its implications for deploying Ricochet in the future at the MITR site as well as the feasibility of reducing this background level via the addition of polyethylene shielding around the detector setup.

Authors:
 [1]; ORCiD logo [2];  [3];  [4];  [1];  [5];  [1];  [5];  [1];  [1];  [1]
  1. MIT
  2. Chicago U., KICP
  3. Lyon, IPN
  4. Northwestern U.
  5. Wisconsin U., Madison
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1407124
Report Number(s):
arXiv:1710.00802; FERMILAB-PUB-17-441-AE
1628106
DOE Contract Number:
AC02-07CH11359
Resource Type:
Journal Article
Resource Relation:
Journal Name: JINST
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Leder, A., Anderson, A. J., Billard, J., Figueroa-Feliciano, E., Formaggio, J. A., Hasselkus, C., Newman, E., Palladino, K., Phuthi, M., Winslow, L., and Zhang, L. Measuring Neutron Spectrum at MIT Research Reactor Utilizing He-3 Bonner Cylinder Approach with an Unfolding Analysis. United States: N. p., 2017. Web.
Leder, A., Anderson, A. J., Billard, J., Figueroa-Feliciano, E., Formaggio, J. A., Hasselkus, C., Newman, E., Palladino, K., Phuthi, M., Winslow, L., & Zhang, L. Measuring Neutron Spectrum at MIT Research Reactor Utilizing He-3 Bonner Cylinder Approach with an Unfolding Analysis. United States.
Leder, A., Anderson, A. J., Billard, J., Figueroa-Feliciano, E., Formaggio, J. A., Hasselkus, C., Newman, E., Palladino, K., Phuthi, M., Winslow, L., and Zhang, L. 2017. "Measuring Neutron Spectrum at MIT Research Reactor Utilizing He-3 Bonner Cylinder Approach with an Unfolding Analysis". United States. doi:. https://www.osti.gov/servlets/purl/1407124.
@article{osti_1407124,
title = {Measuring Neutron Spectrum at MIT Research Reactor Utilizing He-3 Bonner Cylinder Approach with an Unfolding Analysis},
author = {Leder, A. and Anderson, A. J. and Billard, J. and Figueroa-Feliciano, E. and Formaggio, J. A. and Hasselkus, C. and Newman, E. and Palladino, K. and Phuthi, M. and Winslow, L. and Zhang, L.},
abstractNote = {The Ricochet experiment seeks to measure Coherent (neutral-current) Elastic Neutrino-Nucleus Scattering using dark-matter-style detectors with sub-keV thresholds placed near a neutrino source, such as the MIT (research) Reactor (MITR), which operates at 5.5 MW generating approximately 2.2e18 neutrinos/second at the core. Currently, Ricochet is characterizing the backgrounds at MITR, the main component of which comes in the form of neutrons emitted from the core simultaneous with the neutrino signal. To characterize this background, we wrapped a Bonner cylinder around a He-3 thermal neutron detector, whose data was then unfolded to produce a neutron energy spectrum across several orders of magnitude. We discuss the resulting spectrum and its implications for deploying Ricochet in the future at the MITR site as well as the feasibility of reducing this background level via the addition of polyethylene shielding around the detector setup.},
doi = {},
journal = {JINST},
number = ,
volume = ,
place = {United States},
year = 2017,
month =
}
  • The use of detectors moderated by Bonner spheres of different diameters is a relatively easy and inexpensive method of measuring the energy spectrum of neutron emission sources. Because the number of counts for each sphere diameter can be obtained by integration of the spectrum multiplied by a two-dimensional kernel, the spectrum is obtained from measurement data by means of a deconvolution or unfolding algorithm. Algorithms capable of solving this ill-posed inverse problem are based on iteration, requiring an initial spectrum estimate, extensive computation, and considerable experience on the part of the user. This paper presents a noniterative algorithm based onmore » spectrum models with undetermined parameters. It computes the set of parameters that minimizes the error between the actual Bonner counts measured and those predicted by integration of the resulting spectrum. Examples based on ideal data show that to avoid large spectrum errors caused by small measurement errors, the number of parameters involved must be small, much less than the number of sphere diameters employed. This restriction limits resolution in the spectrum, but the limitation is believed to be inherent in the physical characteristics of the Bonner system, not a defect of the algorithm. The method appears effective, fast, and easy to use.« less
  • In this work a neutron spectrum unfolding code, based on artificial intelligence technology is presented. The code called ''Neutron Spectrometry and Dosimetry with Artificial Neural Networks and two Bonner spheres'', (NSDann2BS), was designed in a graphical user interface under the LabVIEW programming environment. The main features of this code are to use an embedded artificial neural network architecture optimized with the ''Robust design of artificial neural networks methodology'' and to use two Bonner spheres as the only piece of information. In order to build the code here presented, once the net topology was optimized and properly trained, knowledge stored atmore » synaptic weights was extracted and using a graphical framework build on the LabVIEW programming environment, the NSDann2BS code was designed. This code is friendly, intuitive and easy to use for the end user. The code is freely available upon request to authors. To demonstrate the use of the neural net embedded in the NSDann2BS code, the rate counts of {sup 252}Cf, {sup 241}AmBe and {sup 239}PuBe neutron sources measured with a Bonner spheres system.« less
  • Determining the energy-dependent dose equivalent for neutrons is a difficult problem. The slowing-down process that neutrons undergo in moderating detectors destroys their incident energy information, causing the detector response to be a complicated function of energy. The improvement of neutron dosimetry requires experimental determination of neutron energy spectra in irradiation environments. Bonner spheres, which consist of a thermal-neutron scintillator and several polyethylene moderating spheres, are commonly used as a field neutron Spectrometer. A computer code must be used in tandem with the Bonner spheres to produce some approximate neutron spectrum from the sphere data by a technique known as spectralmore » unfolding. The unfolding technique requires at least one of several available Bonner sphere response matrices. The choice of response matrix may strongly affect the end-product spectrum. This paper describes the comparison of the several response matrices currently available.« less
  • Although the energy spectra of neutron radiation cannot be measured directly, knowledge of the neutron spectrum in the workplace is necessary for predictions of personnel radiation doses and shielding design. Bonner spheres consist of a central detector over which polyethylene moderating spheres are placed, permitting measurement of the counting rate for various combinations of the central detector and several moderators. The process of approximating neutron spectra from Bonner sphere count-rate data is known as spectral unfolding and requires knowledge of the energy response of each detector-moderator combination (i.e., a response function). The unfolding process may be sensitive to small changesmore » because the response functions are usually ill conditioned making an accurate set of response functions vital to the unfolding process. Previous response function calculations have been limited to a one-dimensional model of the detector-moderator combination and to binned cross-section sets, already averaged over some representative energy spectrum. Of these available response matrices, UTA4 and SAN4 perform the best in unfolding tests. This paper focuses on the relative performance differences between previously published response functions and those we have calculated by modeling Bonner spheres in three dimensions with the Monte Carlo code MCNP4A.« less
  • A reactor noise approach has been successfully performed at the IPEN/MB-01 research reactor facility in order to determine experimentally the effective delayed neutron parameters {beta}i and {lambda}i in a six-group model and the point kinetic equations. The theory/experiment comparison shows that for the abundances the JENDL3.3 presents the best performance while for the decay constants the revised version of ENDF/B-VI.8 shows the best agreement. As a by-product and a consistency check, the {beta}eff parameter was obtained without the need of the Diven factor and the power normalization and it is in excellent agreement with independent measurements. Also, the {beta}eff resultmore » is independent on the nuclear data library used in the fitting procedure. The reflector effect appears to be important only for frequencies larger than {beta}eff/{lambda}, and the results for the kinetic parameters are almost the same as for the non-reflected case.« less