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Nondestructive Assay Method of Hidden Explosive with Laser Compton Scattering Gamma-raysApr. 29, 2009We have proposed a nondestructive assay method for measuring chemical compound such as explosive hidden by heavy shields such as iron plates with a thickness of several centimeters. There are many types of explosives, of which compositions are different. Since most explosives include nitrogen and oxygen, we can detect and assign them with measuring both the nitrogen and oxygen at the same time. We have proposed yet a method for measuring an isotope hidden by heavy shields by using nuclear resonance fluorescence (NRF) with an energy tunable laser Compton scattering (LCS) gamma-ray source [1,2]. The NRF gamma-ray energies depend on the nuclear species. With detection of different several key elements, we can detect and assign a shielded explosive (see Fig. 1). A proof-of-principle experiment was carried out with detection of a chemical compound of melamine, C3H6N6, hidden behind heavy shields [3]. The experiment was carried out at a LCS gamma-ray source of an electron storage ring TERAS in the National Institute of Advanced Industrial Science and Technology. The maximum energy of the gamma-rays was approximately 5.0 MeV (see Fig. 2). The weight of the melamine is 35 g. We measure an abundance ratio, 12C/14N, of the melamine shielded by 15-mm-thick iron and 4-mm-thick lead plates with a High-Purity Germanium semi-conductor detector (see Fig. 3). The observed ratio (12C/14N)exp = 0.39 ±0.12 is consistent with (C/N)melamine = 0.5. The present result suggests that our proposed method enables us to detect an explosive hidden in cargo or container at harbors. [1] R. Hajima et al., Journal of Nuclear Science and Technology, 45, 441 (2008). [2] N. Kikuzawa et al., Applied Physics Express 2 036502 (2009). [3] T. Hayakawa et al., Review of Scientific Instrument 80, 045110 (2009).  Fig. 1 Schematic view of nondestructive assay method. Individual Nuclei have excited states with difference excitation energies.  Fig. 2 Energy Spectrum of Induced laser Compton scattering gamma-rays. The maximum energy is about 5 MeV, which is higher than excitation energies of key excited states of 12C and 14N.  Fig. 3 Observed Nuclear Resonance fluorescence gamma-rays. The gamma-rays emitted from 12C and 14N are clearly observed. The gamma-ray of 208Pb is originated from a lead plate located in front of the melamine. |
