Bulk Explosives Detection using Nuclear Resonance Absorption Technique

Summary form only given. The nuclear resonance absorption (NRA) of gamma rays at 9.17 MeV by nitrogen atoms with a significant cross section (~2b) but a rather narrow width of 122 eV is a well studied nuclear phenomenon. The substantial resonance attenuation of the gamma rays was shown to be an effective indicator of high concentration of nitrogen in an object under interrogation. The source of the 9.17 MeV gamma rays is from the radiative capture of 1.75-MeV protons by a ¹³C target, which results in the creation of ¹⁴N in an excited state. Gamma rays of 9.17 MeV are released during the de-excitation process. Analyses of the transmission profile of the 9.17 MeV gamma rays by tomographic techniques will result in the determination of nitrogen concentration, which is a strong signature of high explosives. The success of this method depends on the production of high current proton beams (>1 mA) with small energy spread (<2 keV) and small emittance (<15 pimm-mrad), advanced detector technology, and state-of-the-art tomographic reconstruction algorithms to achieve the desirable throughput rate with acceptable reliability. We will report on a collaboration with several Russian institutions (VNIITF, JINR, BINP, and IFI) to develop a high-current and compact (several meters in circumference) proton cyclotron with a storage ring incorporated with an energy recovery and electron cooling capabilities, which has potential to satisfy the stringent proton beam requirements for practical application of the NRA technique for explosives detection. We will present a conceptual design of the compact proton storage ring system and an estimate of electron cooling time for the proton beam. Preliminary optimization of the production of resonant gamma rays with respect to the proton energy spread will also be presented