There is an increased use of improvised explosive devices (IED), especially for human targets. One of the substances used in these devices is ammonium nitrate. Since this IED substance also contains elements – hydrogen (H), carbon (C), nitrogen (N), oxygen (O). The elemental density (of H, C, O, and N) and elemental density ratio (C/O, N/O, H/N etc) can be used to differentiate it from other substances. Neutrons based techniques are one of the methods for non-destructive these elemental characterization.
For our experiments we are using two sealed neutron tubes. First tubes can produce 108 (maximum) D-T neutrons in ~0.8 μs pulse and 100 (maximum) pulses can be generated per second. Second tube can produce (maximum) 1010 D-T neutrons/s. The neutron output can be pulsed. Pulses of 1.5 μs duration and pulse repetition rate of 10 Hz to 10 kHz can be obtained.
D-T neutrons pulses are impinged on ammonium nitrate samples (0.5 to 1.5 kg) and resultant gamma rays (prompt and due to activation) are recorded using sodium iodide (NaI) and bismuth germanium orthosilicate (BGO) scintillation detectors. To facilitate recording of high count rate a 2 GS/s high speed digitizer with large on board memory and high transfer rate has been used (instead of conventional multi channel analyzer). Preliminary results and analysis will be presented at the conference.
To further refine the technique we are also developing a D-T neutron generator with associated particle detection facility. For this system we have already developed a penning ion source and a 140 kV battery operated SMPS.