Universität zu Köln

Ophoven, Niklas ORCID: 0000-0002-6772-9555 (2024). Gamma rays induced by interactions of fission neutrons measured with the FaNGaS instrument. PhD thesis, Universität zu Köln.

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Abstract

Prompt Gamma Neutron Activation Analysis (PGNAA) using slow neutrons enables the non-destructive chemical element analysis of small samples. For large samples the Prompt Gamma Analysis based on Inelastic Neutron Scattering (PGAINS) compliments PGNAA due to the higher penetration power of fast neutrons. In this work, the PGAINS technique was studied with the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument installed at Hein Maier-Leibnitz Zentrum (MLZ) in Garching. Previously measured γ-ray spectra were analysed to extract fast-neutron spectrum-averaged γ-ray production cross sections for all identified prompt γ-lines arising from the interaction of fast neutrons with the elements carbon (C), oxygen (O), chlorine (Cl), calcium (Ca), lanthanum (La), praseodymium (Pr), cerium (Ce), neodymium (Nd), samarium (Sm), terbium (Tb) and dysprosium (Dy). Additionally, relative intensities were compared to the work of Demidov et al. from 1978 and the elemental detection limits were estimated. Numerical Monte Carlo simulations were performed to optimize FaNGaS for the irradiation of large samples. In order to reduce the flux of scattered neutrons and emitted γs reaching the detector crystal, a filter material must be placed into the collimator opening of the spectrometer. Therefore, the neutron and γ beam attenuation characteristics of different filters were investigated numerically and complemented by simple analytical models. Furthermore, an analytical model was developed to estimate neutron self-shielding and γ-ray self-absorption in large rectangular-shaped samples of unknown composition. In the frame of this work, a total of 779 different fast-neutron-induced prompt γ-lines were evaluated. Compared to the work of Demidov et al., the measurements resulted in 272 additional lines and identification of another 92 lines unreported in any nuclear data library adds decisive value to nuclear spectroscopy. Borated polyethylene with 20 weight percent boron oxide is proposed as filter material and the developed analytical model allows to estimate neutron self-shielding and γ-ray self-absorption in large samples with uncertainties of 2 and 1%, respectively.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Ophoven, Niklas nophoven@smail.uni-koeln.de orcid.org/0000-0002-6772-9555 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-731199
Date:	2024
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > Forschungszentrum Jülich
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Gamma ray UNSPECIFIED Fast neutron UNSPECIFIED Cross section UNSPECIFIED Inelastic scattering UNSPECIFIED
Date of oral exam:	11 June 2024
Referee:	Name Academic Title Jolie, Jan Prof. Dr. Zilges, Andreas Prof. Dr. Strub, Erik PD Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/73119