Detection of radioactive isotopes by using laser Compton scattered g-ray beams R. Hajima a,Ã , N. Kikuzawa a , N. Nishimori a , T. Hayakawa b , T. Shizuma b , K. Kawase b , M. Kando b , E. Minehara c , H. Toyokawa d , H. Ohgaki e a Japan Atomic Energy Agency, Tokai, Ibaraki 319–1195, Japan b Japan Atomic Energy Agency, Kizugawa, Kyoto 619–0215, Japan c Japan Atomic Energy Agency, Tsuruga, Fukui 914–8585, Japan d National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305–0215, Japan e Kyoto University, Gokasho, Uji, Kyoto 611–0011, Japan article info Available online 21 May 2009 Keywords: Laser Compton scattering Nuclear resonance fluorescence g-ray Isotope detection abstract Non-destructive detection and assay of nuclear materials is one of the most critical issues for both the management of nuclear waste and the non-proliferation of nuclear materials. We use laser Compton scattered (LCS) g-ray beams and the nuclear resonance fluorescence (NRF) for the non-destructive detection of radioactive materials. Quasi-monochromatic and energy-tunable LCS g-ray beams help improve the signal-to-noise ratio during NRF measurements. We developed the conceptual design of a high-flux g-ray source with an energy-recovery linac, which produces a g-ray beam at the flux of 10 13 photons=s: In this paper, we discuss the execution of simulation studies using a Monte Carlo code, results of a proof-of-principle experiment for isotope detection, and the status of the development of LCS X-ray and g-ray facilities. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Non-destructive detection and assay of radioactive isotopes in various materials are essential for enabling nuclear power to emerge as a sustainable and secure source of primary energy. Next-generation nuclear power plants will be operated in the recycling mode, rather than in the once-through mode. Spent nuclear fuels are reprocessed and separated into major and minor actinides, recyclable fissile isotopes, and other fission products. Non-destructive detection of isotopes could enable the rapid and accurate assay of millions of tons of nuclear waste; it could also provide the guidance required to dramatically reduce the cost and improve the safety of waste storage and disposal. Detection of clandestine fissile material in cargo and packages is also indispensable for advanced safeguard and non-proliferation in the nuclear power systems. The use of laser Compton scattered (LCS) g-ray beams for the non-destructive detection of radioactive isotopes has been proposed [1,2]. This method of detection is based on nuclear resonance fluorescence (NRF), which provides a unique finger- print for each isotope of the nucleus of interest; this fingerprint is determined by the number of protons and neutrons as shown in Fig. 1 . A quasi-monochromatic and energy-tunable g-ray beam generated by Compton scattering is an ideal source for NRF measurements. A non-destructive detection system for identifying isotopes that uses a LCS g-ray source is shown in Fig. 2. The advantages of the proposed detection system over the existing systems are as follows: (1) non-destructive identification and assay of radioactive and stable isotopes in various targets is possible; (2) the quasi-monochromatic g-ray tuned at fluores- cence energy helps improve the signal-to-noise ratio in energy- resolved g-ray detection system by separating the fluorescence g-ray from the background noise, which is mostly generated through Compton scattering of the incident g-rays in the target; (3) detection of a variety of isotopes is practically possible by scanning the incident g-ray energy. The energy width of g-ray beams for the above application will be 1–10% depending on the number of isotopes to detect at once. Collimation of the g-ray beam by heavy-metal block can be used to obtain such energy spectrum with preserving a sharp decrease at high energies, which is essential for the good signal-to-noise ratio in the NRF measurement. In this paper, our research activities pertaining to the LCS g-ray/NRF system for isotope detection are discussed. 2. Proposal of a high-flux g-ray facility For non-destructive detection of radioactive isotopes on an industrial scale, we have designed a high-flux g-ray facility ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.05.063 Ã Corresponding author. E-mail address: hajima.ryoichi@jaea.go.jp (R. Hajima). Nuclear Instruments and Methods in Physics Research A 608 (2009) S57–S61