MODES_SNM Modular Detection System for Special Nuclear Material FP7-SEC G. Viesti Dipartimento di Fisica ed Astronomia Università di Padova

INTRODUCTION / 1 The detection and identification of radioactive sources and Special Nuclear Material (HEU and WGPu) is one of the higher priority task in the field of counter-CBRN programs. This task is certainly connected with the possibility of terrorist actions (RDD or nuclear weapons) but it has also important consequences on the public health in case of contaminated merchandises. The screening is performed normally with RADIATION PORTAL MONITORS that detect gamma ray by using high efficiency but low resolution plastic scintillator detectors (PVT) providing an alarm based on excess counts only. Similarly, 3 He based proportional counters have been used so far to detect neutrons. THE RPM represents the first level screening. In case of alarm, a second level inspection is operated by using portable systems providing gamma-ray spectroscopic information by using inorganic scintillators (NaI(Tl) or LaBr(Ce)) or even HPGe detectors. Today’s problems: 1) NORM discrimination (false alarm rate) 2) 3He crisis for the production of detectors 3) need to improve the neutron detection to search for SNM

INTRODUCTION / 2 Topic SEC Development of detection capabilities of difficult to detect radioactive sources and nuclear materials As underlined in the EU CBRN action plan, efficient and reliable detection of difficult-to-detect radioactive sources and nuclear materials, including masked and shielded sources, is still a challenge. The research project should look specially into solutions for the improvement of detection and enhancing the portability and mobility of detection solutions, which could among other be used also by emergency responders in the field or for the detection and location of a radiation source in large crowds. The solutions proposed should facilitate reliable and correct assessment of the detected signal for subsequent launching of appropriate response.  1) fast relocatable solution 2) end-user oriented 3) detection and localization of sources 4) improve the detection capability of “difficult sources” 5) identification of the source MODES_SNM PROJECT IS SUPPOSED TO MEET REQUIREMENTS AND EXPECTATIONS

BASIC FACTS / NEEDS Detection of radioactive sources: False gamma-ray alarms generated by NORM  Need of spectroscopic capability Detection of SNM: Pu isotopes are prolific fast neutron sources Specific gamma-ray signatures U samples: very low neutron emission Specific gamma-ray signatures  Need of spectroscopic capability Need of very good capability to distinguish weak fast neutron signal from background Masked sources: Spectroscopic capability Need of detecting neutrons in a very high gamma background Shielded sources: Need of very good capability to distinguish weak fast neutron signal from background Thermal neutron detection Pu HEU LEU

STATE-OF-THE-ART vs MODES_SNM THE NEUTRON CASE Origin of the terrestrial neutron background: spallation reaction induced by the cosmic ray particles (typically 20 counts/s per m 2 of detector,1/E dependence) State-of-the art: 3He-poly assembly good efficiency from thermal to 10 MeV MODES_SNM: fast neutron detector ( MeV) with efficiency centered in the SNM fast neutron spectrum. Terrestrial background is minimized thus enhancing the detection capability of weak fast neutron signal. Special thermal neutron detectors (without poly moderator). The measure of the fast/thermal neutron ratio will provide information about the presence of shield.

THE MODES_SNM FAST NEUTRON TECH High pressure fast neutron 4He scintillation detectors developed by ARKTIS (Zurich) Distinctive facts: 1)Good efficiency for fast neutrons and low efficiency for gamma rays 2)Neutron-gamma discrimination capability  It operates in a high gamma ray background  Possibility of energy windowing Optimization of the mechanical lay-out and the read-out of the gas scintillation cell to enhance portability New electronics front-end from CAEN

GAMMA RAY DETECTORS: Xenon high pressure scintillation cells (i.e. cells using the same basic technology of the ARKTIS fast neutron detectors). Xenon exhibits outstanding properties both as a scintillation and as an ionization medium and a high absorption for gamma rays. Consequently xenon is a very interesting material for gamma ray detection and spectroscopy. Good energy resolution with an efficiency exceeding 10% for gamma energies up to 1 MeV can be achieved with high-pressure xenon scintillation cells of modest dimensions (12 cm diameter at ~60 bar). FFrom: MODES_SNM GAMMA-RAY TECH

MODES_SNM THERMAL NEUTRON TECH THERMAL NEUTRON DETECTOR: gas cells with a suitable converter of the thermal neutrons in charged particles. The goal is to detect the charged particle products in a low pressure noble gas scintillation cell (the basic ARKTIS technology) to detect the charged particles (short range) but being insensitive to fast neutrons and gamma rays. 10 B 4 C lined detector

FRONT-END ELECTRONICS HV power supplies and fast-digitizers will be designed and produced by CAEN specifically for matching the MODES_SNM requirements: 1)optimized for the read-out of the ARKTIS high pressure scintillation detectors 2) on-board Digital Pulse Processing will determine on-line the relevant event parameters (i.e. type of particle, energy….) 3) low power consumption to provide sufficient battery life time and enhance the system portability

The MODES_SNM demonstrator The demonstrator will be a modular and scalable system divided into so- called system blocks. To enhance the mobility and flexibility, each system block weighs less than 25 kg, allowing it to be placed and removed into/onto vehicles. Block A consists of all system electronics including power supply and battery, signal processing electronics, analysis units, and the user interface. Blocks B consists of arrays of four detector modules per block, selected from the suite of gamma, fast neutron and thermal neutron radiation detector modules. Each Block A will serve several blocks type B The MODES_SNM prototype represents a type of instruments defined as PORTABLE RADIATION SCANNER by IAEA. In this context few types of operations are foreseen: 1)Mobile configuration: i.e. van mounted search 2)Stationary mode (i.e. pedestrian or road vehicle monitor even in connection with X-ray scanners) For each type of operation different Blocks B are needed and a specific Information System will be prepared.

FIELD DEMONSTRATION An end-user group will be organized with the participation of the European agencies for border control and law-enforcement. The first part of the demonstration will be organized at the Padova University where strong gamma ray and neutron sources are available. After a training course, blind tests operated directly by end-users will be organized. This activity (training + blind tests) will take one working week. After this first step, field demonstrations will be organized at least in three different European locations selected by the end-user group in which blind tests can be organized by using different types of NORM material to verify the capability of the system to locate and identify weak sources. The use of NORM will avoid licensing problems. Each field demonstration will last typically one week with the support of all project participants. During each field test the system will be operated by end-users only.

PROJECT PARTICIPANTS

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