Special nuclear material detection with a mobile multi-detector system D. Cester a , G. Nebbia b , L. Stevanato a,b , G Viesti a,b,n , F. Neri c , S. Petrucci c , S. Selmi c , C. Tintori c , P. Peerani d , A. Tomanin d a Dipartimento di Fisica, Universit  a di Padova, Via Marzolo 8, I-35131 Padova, Italy b INFN Sezione di Padova, Via Marzolo 8, I-35131 Padova, Italy c CAEN S.p.A., Via Vetraia 11, I-55049 Viareggio (LU), Italy d European Commission EC–JRC–ITU, I-21027 Ispra, Italy article info Article history: Received 16 August 2011 Received in revised form 7 October 2011 Accepted 12 October 2011 Available online 20 October 2011 Keywords: Special nuclear material Mobile detection system Digital signal processing Neutron and gamma ray measurements Neutron induced reactions abstract The detection of special nuclear material has been studied with a mobile inspection system used both as a high sensitivity passive neutron/gamma spectroscopic tool and as an active inspection device using tagged neutrons. The detection of plutonium samples seems to be possible with passive interrogation, even for small samples, thanks to the yield of gamma ray and neutrons. Moreover the gamma ray spectrum shows clear signatures related to 239 Pu. The passive detection of uranium is much more difficult because of the low neutron yield and of the easiness of shielding the gamma ray yield of highly enriched U samples. However, we show that active interrogation with tagged neutrons is able to provide signatures for the discrimination of uranium against other heavy metals. & 2011 Elsevier B.V. All rights reserved. 1. Introduction The SLIMPORT project [1], financed by the Italian Ministry for the Economic Development (MISE), is dedicated to the development of an integrated toolbox forming a complete security system to monitor the flow of persons and merchandise in harbors. In this framework, a mobile inspection station (called SMANDRA, the Italian acronym stands for Sistema Mobile per Analisi Non Distruttive e RAdio- metriche) has been developed. The system is conceived as an instrument to perform non-destructive analysis, usable in conjunc- tion with the present monitoring devices such as radiation portal monitors, x-ray scanners and others. The aim of the system is to detect and identify sources of ionizing radiation or dangerous and/or illegal materials inside volumes tagged as ‘‘suspect’’ by conventional X-ray scanners. The system is made of two parts: a. A passive unit including gamma ray and neutron detectors. The unit hosts batteries, power supplies, front-end electronics and CPU. b. An active unit including a portable sealed neutron generator used to produce tagged neutron beams. The first unit can be used in a standalone mode as a high efficiency spectroscopic radiometer for the detection and identi- fication of ionizing radiation such as gamma rays, fast and thermal neutrons produced by radioactive sources or Special Nuclear Material (SNM). It can be used as well as a detector package connected to the second unit for active interrogation of voxels inside a load using the Tagged Neutron Inspection System (TNIS) technique [2]. The application of the SMANDRA multi-detector system to the detection of SNM is described in this paper. Laboratory results are reported for passive as well as for active interrogations of SNM. 2. The SMANDRA system A complete description of the SMANDRA system is presented in Ref. [3], here we report only the relevant parameters of the system. The dual use of SMANDRA (active and passive interrogations) sets stringent requirements: (a) low background, high efficiency detec- tors for gamma and neutrons, (b) capability of discriminating the two components of the radiation in the passive mode and (c) high count rate capability to operate in coincidence with the associated particle counter hosted in the neutron generator. Photon spectroscopy is performed using a high resolution 2 00  2 00 BrilLanCe TM 380 LaBr(Ce) detector and a high efficiency large volume 5 00  5 00 NaI(Tl) scintillator. The LaBr(Ce) detector offers the ultimate energy resolution for scintillators but suffers Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2011.10.011 n Corresponding author at: Dipartimento di Fisica, Universit  a di Padova, Via Marzolo 8, I-35131 Padova, Italy. Tel./fax: þ39 8275933. E-mail address: viesti@pd.infn.it (G. Viesti). Nuclear Instruments and Methods in Physics Research A 663 (2012) 55–63