Rapid interrogation of special nuclear materials by combining scattering and transmission nuclear resonance fluorescence spectroscopy

The smuggling of special nuclear materials(SNMs)across national borders is becoming a serious threat to nuclear nonproliferation.This paper presents a feasibility study on the rapid interrogation of concealed SNMs by combining scattering and transmission nuclear resonance fluorescence(s NRF and t NRF)spectroscopy.In s NRF spectroscopy,SNMs such as^(235,238)U are excited by a wide-band photon beam of appropriate energy and exhibit unique NRF signatures.Monte Carlo simulations show that one-dimensional scans can realize isotopic identification of concealed^(235,238)U when the detector array used for interrogation has sufficiently high energy resolution.The simulated isotopic ratio^(235U/238)U is in good agreement with the theoretical value when the SNMs are enclosed in relatively thin iron.This interrogation is followed by t NRF spectroscopy using a narrow-band photon beam with the goal of obtaining tomographic images of the concealed SNMs.The reconstructed image clearly reveals the position of the isotope^(235)U inside an iron rod.It is shown that the interrogation time of s NRF and t NRF spectroscopy is one order of magnitude lower than that when only t NRF spectroscopy is used and results in a missed-detection rate of 10^(-3).The proposed method can also be applied for isotopic imaging of other SNMs such as^(239,240)Pu and^(237)Np.