Ph.d. degree
Hebrew University of Jerusalem, Israel, 2014

Michal Brandis

Supervisor: D.Vartsky, E. Friedman

Development of a Gamma-Ray Detector for Z-Selective Radiographic Imaging

Keywords:

• Search for radioactive and fissile materials
• Inspection with gamma rays
• Inspection with neutrons

Abstract:

Dual-Discrete Energy Gamma-Radiography (DDEGR) is a method for Special Nuclear Materials (SNM) detection. DDEGR utilizes 15.11 and 4.43 MeV gamma-rays produced in the 11B(d,n)12C reaction, in contrast to the conventional use of continuous Bremsstrahlung radiation.
The clean and well separated gamma-rays result in high contrast sensitivity, enabling detection of small quantities of SNM. The most important aspects of a DDEGR system were discussed, simulated, measured and demonstrated.
An experimental measurement of gamma-ray yields from the 11B(d,n)12C reaction showed that the yields from deuterons with 3—12 MeV energy are 2—20×1010 gamma/sr/mC 4.4 MeV gamma-rays and 2—5×109 gamma/sr/mC 15.1 MeV gamma-rays. The measured neutron yields show that the neutron energies extend to 15-23 MeV for the same deuteron energy range.
A simplified inspection system was simulated with GEANT4, showing that the effect of scattering on the signal measured in the detector is acceptable. Considering the reaction gamma yields, 1.8 mA deuteron current is required for separation of high-Z materials from medium- and low-Z materials and a 4.5 mA current is required for the additional capability of separating benign high-Z materials from SNM. The main part of the work was development of a detector suitable for a DDEGR system — Time Resolved Event Counting Optical Radiation (TRECOR) detector. TRECOR detector is a novel spectroscopic imaging detector for gamma-rays within the MeV energy range that uses an event counting image intensifier with gamma-rays for the first time.
Neutrons that accompany the gamma radiation enable to implement, in parallel, Fast Neutron Resonance Radiography (FNRR), a method for explosives detection. A second generation detector, TRECOR-II, is capable of detecting gamma-rays and neutrons in parallel, separating them to create particle-specific images and energy-specific images for each particle, thus enabling simultaneous implementation of the two detection methods.
A full DDEGR laboratory prototype was constructed using the specially-developed TRECOR-II detector and the 11B(d,n)12C nuclear reaction as a source. The separation of SNM from other materials including benign high-Z materials was demonstrated. The results of the simulations, calculations and experimental studies support the viability of the proposed DDEGR inspection method and constitute a proof-of-principle.