Karim Boudergui

Moving Sources Detection Algorithm for Radiation Portal Monitors Used in a Linear Network

To monitor radioactivity passing through a vehicle such as a pedestrian, a car, a train or a truck, Radiation Portal Monitors (RMP) are commonly employed. These detection systems consist of a large volume detector set close to the potential source path. An alarm is then triggered when the signal rises over a threshold initially estimated in view of the natural background signal. The approach developed in this work makes use of several detectors in a network along the source path. The correlation detection approach is elaborated to take into account the temporal periodicity of the signals taken by all distributed sensors as a whole. This new detection method is then not based only on counting statistics but also on the temporal series analysis. Therefore, a specific algorithm has been developed in our laboratory for this security application and shows a significant improvement, especially in terms of detection probability increase and false alarm reduction. This paper presents the theoretical approach and promising results obtained by simulation.

Data Acquisition and Analysis of the UNCOSS Underwater Explosive Neutron Sensor

The purpose of the FP7 UNCOSS project (Underwater Coastal Sea Surveyor, http://www.uncoss-project.org) is to develop a neutron-based underwater explosive sensor to detect unexploded ordnance lying on the sea bottom. The Associated Particle Technique is used to focus the inspection on a suspicious object located by optical and electromagnetic sensors and to determine if there is an explosive charge inside. This paper presents the data acquisition electronics and data analysis software which have been developed for this project. A field programmable gate array that digitizes and processes the signal allows to perform precise time-of-flight and gamma-ray energy measurements. The gamma-ray spectra are unfolded into pure elemental count proportions, mainly C, N, O, Fe, Al, Si, and Ca. The C, N, and O count fractions are converted into chemical proportions, taking into account the gamma-ray production cross sections, as well as neutron and photon attenuation in the different shields between the ROV (Remotely Operated Vehicle) and the explosive, such as the explosive iron shell, seawater, and ROV envelop. A two-dimensional (2D) barycentic representation of the C, N, and O proportions is built from their chemical ratios, and a 2D likelihood map is built from the associated statistical and systematic uncertainties. The threat level is evaluated from the best matching materials of a database including explosives.

Detection of special nuclear materials with the associate particle technique

In the frame of the French trans-governmental R&D program against chemical, biological, radiological, nuclear and explosives (CBRN-E) threats, CEA is studying the detection of Special Nuclear Materials (SNM) by neutron interrogation with fast neutrons produced by an associated particle sealed tube neutron generator. The deuterium-tritium fusion reaction produces an alpha particle and a 14 MeV neutron almost back to back, allowing tagging neutron emission both in time and direction with an alpha particle position-sensitive sensor embedded in the generator. Fission prompt neutrons and gamma rays induced by tagged neutrons which are tagged by an alpha particle are detected in coincidence with plastic scintillators. This paper presents numerical simulations performed with the MCNP-PoliMi Monte Carlo computer code and with post processing software developed with the ROOT data analysis package. False coincidences due to neutron and photon scattering between adjacent detectors (cross talk) are filtered out to in...

New monitoring system to detect a radioactive material in motion

Illegal radioactive material transportation detection, by terrorist for example, is problematic in urban public transportation. Academics and industrials systems include Radiation Portal Monitor (RPM) to detect radioactive matters transported in vehicles or carried by pedestrians. However, todays RPMs are not able to efficiently detect a radioactive material in movement. Due to count statistic and gamma background, false alarms may be triggered or at the contrary a radioactive material not detected. The statistical false alarm rate has to be as low as possible in order to limit useless intervention especially in urban mass transportation. The real-time approach depicted in this paper consists in using a time correlated detection technique in association with a sensor network. It is based on several low-cost and large area plastic scintillators and a digital signal processing designed for signal reconstruction from the sensor network. The number of sensors used in the network can be adapted to fit with applications requirements or cost. The reconstructed signal is improved by comparing other approaches. This allows us to increase the device speed that has to be scanned while decreasing the risk of false alarm. In the framework of a project called SECUR-ED Secured Urban Transportation - European Demonstration, this prototype system will be used during an experiment in the Milan urban mass transportation.

Moving sources detection system

To monitor radioactivity passing through a pipe or in a given container such as a train or a truck, radiation detection systems are commonly employed. These detectors could be used in a network set along the source track to increase the overall detection efficiency. However detection methods are based on counting statistics analysis. The method usually implemented consists in trigging an alarm when an individual signal rises over a threshold initially estimated in regards to the natural background signal. The detection efficiency is then proportional to the number of detectors in use, due to the fact that each sensor is taken as a standalone sensor. A new approach is presented in this paper taking into account the temporal periodicity of the signals taken by all distributed sensors as a whole. This detection method is not based only on counting statistics but also on the temporal series analysis aspect. Therefore, a specific algorithm is then developed in our lab for this kind of applications and shows a significant improvement, especially in terms of detection efficiency and false alarms reduction. We also plan on extracting information from the source vector. This paper presents the theoretical approach and some preliminary results obtain in our laboratory.

A generic isotope identification approach for nuclear instrumentation

Isotope identification is generally done from spectra from high intrinsic resolution such as germanium. A lot of approaches are proposed in the literature. Most of them are not efficient with poor energy resolution detectors such as non-loaded scintillators. The proposed approach is a new isotope identification principle to deal with the overall range of nuclear detectors. The proposed method allows the identification of isotopes using detectors with poor intrinsic resolution and lower counting than the existing techniques.

Detection of special nuclear materials with tagged neutrons

The Associated Particle Technique can be used to detect Special Nuclear Materials in cargo containers. A DT neutron generator, based on the 3H(2H,n)α fusion reaction, produces 14 MeV neutrons which are tagged both in direction and time with an embedded alpha detector. Prompt neutrons and gamma rays emitted during neutron-induced fissions are detected by plastic scintillators, in coincidence with the alpha particle. Nuclear materials are differentiated from non-nuclear materials and crosstalk events using high multiplicity coincidences. The data acquisition electronics is made of compact FPGA boards. Experiments performed with a mock-up of the measurement system are reported and compared to calculations to validate numerical simulation and post-processing tools. Measurements have been performed with different targets made of iron, lead, or uranium, placed in metallic or wood cargo matrixes. The performances of a full scale cargo container inspection system, with a larger number of detectors optimized for container inspection, are also studied by numerical simulation. Random background due to neutrons which are not correlated with an alpha particle, counting statistics, time and energy resolutions of the data acquisition system, are all taken into account to model the measurements as realistically as possible. A wide range of inspections, with the suspicious item in different positions in different cargo matrixes, have been studied.

Implementation of gadolinium for neutron measurement systems based on plastic scintillators and semiconductors

CEA LIST has investigated different schemes enabling neutron detection thanks to the implementation of gadolinium converters. The fine analysis of the prompt gamma ray signature has permitted us to propose and test dedicated designs such as Gd-doped plastic scintillator, large spherical scintillators or compensated CdZnTe diodes.

Neutron detection with large plastic scintillators for RPM applications

Homeland security requests the use Radiation Portal Monitor (RPM) to detect and differentiate gamma and neutron radiation. Gamma detection is required for illicit transportation of radioactive matter detection. Neutron detection is important to control nonproliferation of enriched material. Manufacturers worldwide propose sensors based on 3He which give the actual state of art in term of neutron detection. The price fluctuations due to the announcement of the shortage of 3He forces manufacturers to find viable alternative. From 10 years sensors providers have the challenge to replace previous 3He detectors that are known to be the most commonly deployed neutron sensor. As 3He detectors can only detect neutron, they must be completed with gamma detector. The proposed approach is based on pulse time correlation between adjacent sensors from signal collected by EJ200 plastic scintillators to detect gamma and neutron. Results obtained during FP7 Scintilla project test campaigns show the system relevance for replacement of todays 3He detectors.

Hypothesis tests for the detection of constant speed radiation moving sources

As a complement to single and multichannel detection algorithms, inefficient under too low signal-to-noise ratios, temporal correlation algorithms have been introduced to detect radiological material in motion. Test hypothesis methods based on the mean and variance of the signals delivered by the different channels have shown significant gain in terms of a tradeoff between detection sensitivity and false alarm probability. This paper discloses the concept of a new hypothesis test for temporal product detection methods, taking advantage of the Poisson nature of the registered counting signals, and establishes a benchmark between this test and its empirical counterpart. The simulation study validates that in the two relevant configurations of a pedestrian source carrier under respectively high and low count rate radioactive backgrounds, the newly introduced hypothesis test ensures a significantly improved compromise between sensitivity and false alarm, while guaranteeing the stability of its optimization parameter regardless of signal-to-noise ratio variations between 2 to 0.8.