Schematic description of the GNT technology Calculated bremsstrahlung X-ray spectra for various electron beam energies X-ray intensity distributions for various electron beam energies GNT technology system block diagram 2.2 2.3 HESCO Mini-Linatron system components 2.4 Overview of VARITRON unit 2.5a VARITRON schematic: top-view 2.5b VARITRON schematic: side-view Block diagram of field-deployed GNT system 2.6 2.7 VARITRON beam analysis assembly 2.8 2.9 VARITRON control console 2.10 GNT detection system Internal view of VARITRON unit Upgraded VARITRON beam analysis assembly Deployed, tripod-mounted GNT detector 2.1 1 2.12 GNT detector assembly schematic 2.13 Graphical representation of a detection channel response 3.1 3.2 3 4 5 9 11 14 15 24 29 VARITRON performance curves (peak bending magnet current vs injection current) for various magnetron currents Peak bending magnet current versus electron beam kinetic energy 35 iv 3.3 4.1 4.2 4.3 4.4 5.1 5.2 5.3 Measured energy-dependent electron distribution profiles and corresponding integrated responses for several operational conditions Prompt neutron signatures for beryllium, heavy water, and depleted uranium Delayed neutron signatures for beryllium, heavy water, and depleted uranium Prompt neutron signature for combined beryllium and heavy water target with and without depleted uranium Delayed neutron signatures for combined beryllium and heavy water target with and without depleted uranium Nominal testing configuration in ISU test cell Graphical MDL representation Various testing configurations 36 44 48 * Current-Sensitive; t Double D i f f e r e n t i a t i o n C i r c u i t

A photonuclear interrogation method was experimentally assessed for the detection of shielded nuclear materials. Proof-of-Concept assessment was performed at the Los Alamos National Laboratory (LANL) TA-18 facility and used the INEEL VARITRON electron accelerator. Experiments were performed to assess and characterize the delayed neutron emission responses for different nuclear materials with various shield configurations using three "nominal" electron beam energies; 8-, 10-, and 11-MeV. With the exception of highly enriched uranium (HEU), the nuclear materials assessed represent material types commonly encountered in commerce. The specific nuclear materials studied include a solid 4.8-kg HEU sphere, a 5-kg multiple -object, depleted uranium (DU) [uranium with about 0.2% enrichment with U-235] target, and two 11-kg thorium disks. The shield materials selected include polyethylene, boratedpolyethylene, and lead. Experimental results, supported with numerical predictions, have shown that the photonuclear interrogation technique is quite capable of detecting shielded nuclear material via the direct measurement of the photofission-induced delayed neutron emissions. To identify or discriminate between nuclear material types (i.e., depleted uranium, HEU, and thorium), a ratio of delayed neutron counts at two different beam energies is utilized. This latter method, referred to as the dual-beam energy ratio Figure-

No abstract

A photonuclear interrogation method was experimentally assessed for the detection of shielded nuclear materials. Proof-of-Concept assessment was performed at the Los Alamos National Laboratory (LANL) TA-18 facility and used the INEEL VARITRON electron accelerator. Experiments were performed to assess and characterize the delayed neutron emission responses for different nuclear materials with various shield configurations using three "nominal" electron beam energies; 8-, 10-, and 11-MeV. With the exception of highly enriched uranium (HEU), the nuclear materials assessed represent material types commonly encountered in commerce. The specific nuclear materials studied include a solid 4.8-kg HEU sphere, a 5-kg multiple -object, depleted uranium (DU) [uranium with about 0.2% enrichment with U-235] target, and two 11-kg thorium disks. The shield materials selected include polyethylene, boratedpolyethylene, and lead. Experimental results, supported with numerical predictions, have shown that the photonuclear interrogation technique is quite capable of detecting shielded nuclear material via the direct measurement of the photofission-induced delayed neutron emissions. To identify or discriminate between nuclear material types (i.e., depleted uranium, HEU, and thorium), a ratio of delayed neutron counts at two different beam energies is utilized. This latter method, referred to as the dual-beam energy ratio Figure-

No abstract