The Statistics of Emission and Detection of Neutrons and Photons
Licentiatavhandling, 2008

One particular purpose of nuclear safeguards, in addition to accounting for known materials, is the detection, identifying and quantifying unknown material, to prevent accidental and clandestine transports and uses of nuclear materials. This can be achieved in a non-destructive way through the various physical and statistical properties of particle emission and detection from such materials. This thesis addresses some fundamental aspects of nuclear materials and the way they can be detected and quantified by such methods. Factorial moments or multiplicities have long been used within the safeguard area. These are low order moments of the underlying number distributions of emission and detection. One objective of the present work was to determine the full probability distribution and its dependence on the sample mass and the detection process. Derivation and analysis of the full probability distribution and its dependence on the above factors constitutes the first part of the thesis. Another possibility of identifying unknown samples lies in the information in the "fingerprints" (pulse shape distribution) left by a detected neutron or photon. A study of the statistical properties of the interaction of the incoming radiation (neutrons and photons) with the detectors constitutes the second part of the thesis. The interaction between fast neutrons and organic scintillation detectors is derived, and compared to Monte Carlo simulations. An experimental approach is also addressed in which cross correlation measurements were made using liquid scintillation detectors. First the dependence of the pulse height distribution on the energy and collision number of an incoming neutron was derived analytically and compared to numerical simulations. Then an algorithm was elaborated which can discriminate neutron pulses from photon pulses. The resulting cross correlation graphs are analyzed and discussed whether they can be used in applications to distinguish possible sample signatures to identify unknown nuclear materials.

multiplicities

nuclear safeguards

Number distribution

scintillation detectors

light pulse distribution

fissile material

cross correlations

Nuclear Engineering seminar room, 3rd floor Soliden
Opponent: Dr. S. B. Degweker

Författare

Andreas Enqvist

Chalmers, Teknisk fysik, Nukleär teknik

Monte Carlo and analytical models of neutron detection with organic scintillation detectors

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,; Vol. 582(2007)p. 629-637

Artikel i vetenskaplig tidskrift

The number distribution of neutrons and gamma photons generated in a multiplying sample

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,; Vol. 566(2006)p. 598-608

Artikel i vetenskaplig tidskrift

The Number Distribution and Factorial Moments of Neutrons and Gamma Photons Generated in a Multiplying Sample

JNMM, Journal of the Institute of Nuclear Materials Management,; Vol. XXXV(2006)p. 29 - 35

Artikel i vetenskaplig tidskrift

Measurement and simulation of neutron/gamma-ray cross-correlation functions from spontaneous fission

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,; Vol. 595(2008)p. 426-430

Artikel i vetenskaplig tidskrift

The Detection Statistics of Neutrons and Photons Emitted from a Fissile Sample.

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,; Vol. 607(2009)p. 451-457

Artikel i vetenskaplig tidskrift

Ämneskategorier

Subatomär fysik

Övrig annan teknik

CTH-NT - Chalmers University of Technology, Nuclear Engineering: 214

Nuclear Engineering seminar room, 3rd floor Soliden

Opponent: Dr. S. B. Degweker