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We present the findings of the probabilistic radiological characterization exercise conducted within the EU project MICADO "Measurement and Instrumentation for Cleaning and Decommissioning Operations". A Bayesian inversion approach that accounts for uncertainty in the measurement efficiencies is used to interpret combinations of (i) segmented gamma scanning (SGS) spectrometry, (ii) passive neutron coincidence counting (PNCC) and (iii) active neutron interrogation (AN), in a fully virtual experiment. The considered Bayesian approach treats uncertainty in the measurement efficiencies by doing multilinear interpolation between reference efficiencies representing potential "end-member" waste matrices with respect to both composition and density, with the end-member proportions being jointly inferred with the other unknowns. The performance of the approach in terms of efficiency and accuracy is explored for two virtual case studies of increasing complexity, that are based on common, real waste packages. The used Bayesian approach appears to be fast and rather accurate for the first considered waste package. With respect to the second waste package which has a substantially more complex and heterogeneous matrix structure, some biases are noticed in the derived posterior mass distributions of the nuclides of interest. We thus discuss possible causes and solutions for these discrepancies. In addition, we devise an R package that wraps the probabilistic models in an HTTP API so that the user can send HTTP requests to a remote server that runs the computations and returns the obtained results. This should allow using the approach in a production environment. • Proof of concept of probabilistic radiological characterization in production. • Joint inversion of gamma spectrometry, passive neutron coincidence counting and active neutron interrogation. • The approach accounts for measurement errors and the uncertainty associated with the waste matrix and the isotopic vector. [ABSTRACT FROM AUTHOR]

Delayed gamma-ray spectroscopy (DGS) is an active-interrogation nondestructive assay technique that can be used to determine the composition of a nuclear material sample by comparing the ratios of fission product gamma-ray peak intensities. However, high-radioactivity nuclear material (HRNM) contains long-lived fission products that can overwhelm a detector and shielding must be used to reduce the count rate, while minimally affecting those gamma rays from short-lived fission products with energy above 3-MeV. To compensate for the signal loss through the shielding, low-energy neutrons are required to induce more fission events from the high thermal cross-section of fissile nuclides. To improve practical safeguards DGS capabilities, we are developing a compact interrogation system to moderate ∼ 2-MeV neutrons that are easier to moderate than 14-MeV neutrons from standard deuterium-tritium generators. This work describes the optimization of an ideal moderator system for a 252Cf neutron point source that results in a neutron fluence of 25.9 × 10 − 4 cm−2 n source − 1 passing through the sample space with ≳ 70% of those below 1-eV. Modifications for practical fabrication resulted in ⩽ 20 % reductions of the flux compared to the optimized ideal design. Finally, evaluations made of HRNM DGS signals and backgrounds conclude that a 252Cf source intensity of 8.9 × 10 7 neutrons per second is required for a single-pass interrogation within this ideal moderator system. However, this can be as low as 3.6 × 10 6 neutrons per second using smaller samples that require less shielding. • Moderator optimized to increase the flux by a factor of 20–30 in the sample space. • Direct 70 to > 100 % of the source neutrons into the sample space. • Increase the thermal-to-fast neutron ratio by a factor of > 1000. • 20% reductions resulting from practical modifications for fabrication potential. • Need ⩽ 6 % of the source neutrons compared to a DT generator under similar conditions. [ABSTRACT FROM AUTHOR]

A neutron-based sensor has been developed able to measure the water cut and the chlorine content in crude oil. The sensor is based upon the use of a pulsed fast neutron source. Two different cases were studied. Case "A": chlorine detection with no water present and case "B": water cut measurements with no chlorine present. The minimum detection limits for case A and case B were found to be (62 ± 6) mg/L and (2 ± 2) vol%, respectively. • A neutron sensor for on-line determination of water-cut and chlorine impurities in crude oil was developed. • Measurements were done on geological samples taken from Croatian oilfields and on standard samples prepared in the laboratory. • Since both chlorine and oxygen have similar gamma-ray lines at 6.1 MeV, these two were separated by choosing a different pulsing frequency for the neutron beam. • A similar setup (neutron probe) could be easily made for monitoring individual wells. [ABSTRACT FROM AUTHOR]

The Italian National Agency for New Technologies, Energy, and Sustainable Economic Development (ENEA) Neutron Active Interrogation (NAI) device is a tool designed to improve CBRNE defense. It is designed to uncover radioactive and nuclear threats including those in the form of Improvised Explosive Devices (IEDs), the so-called "dirty bombs". The NAI device, at its current development stage, allows to detect 6 g of 235U hidden in a package. It is easily transportable, light in weight, and with a real-time response. Its working principle is based on two stages: (1) an "active" stage in which neutrons are emitted by a neutron generator to interact with the item under inspection, and (2) a "passive" stage in which secondary neutrons are detected originating a signal that, once processed, allows recognition of the offence. In particular, a clear indication of the potential threat is obtained by a dedicated software based on the Differential Die-Away Time Analysis method. [ABSTRACT FROM AUTHOR]

In order to perform Quality Assurance/Quality Control (QA/QC) procedures for a system dedicated to the neutron interrogation of objects for the presence of threat materials one needs to perform measurements of reference materials (RM) i.e. simulants having the same (or similar) atomic ratios as real materials. It is well known that explosives, drugs, and various other benign materials, contain chemical elements such as hydrogen, oxygen, carbon and nitrogen in distinctly different quantities. For example, a high carbon-to-oxygen ratio (C/O) is characteristic of drugs. Explosives can be differentiated by measurement of both (C/O) and nitrogen-to-oxygen (N/O) ratios. The C/N ratio of the chemical warfare agents, coupled with the measurement of elements such as fluorine and phosphorus, clearly differentiate them from the conventional explosives. Here we present the RM preparation, calibration procedure and correlations attained between theoretical values and experimentally obtained results in laboratory conditions for C/O and N/C ratios of prepared hexogen (RDX), TNT, DLM2, TATP, cocaine, heroin, yperite, tetranitromethane, peroxide methylethylketone, nitromethane and ethyleneglycol dinitrate simulants. We have shown that analyses of the gamma ray spectra by using simple unfolding model developed for this purpose gave a nice agreement with the chemical formula of created simulants, thus the calibration quality was successfully tested. [ABSTRACT FROM PUBLISHER]

Earlier efforts have identified an algorithm that uses active neutron interrogation to find explosives hidden in cargo containers. This algorithm uses flags, in the form of specific mathematical manipulations of the exiting neutron and photon radiation at different angles, to classify the cargo type, search for hidden explosives, and minimize certain false positives due to cargo heterogeneities. Statistical modeling software has now been applied to the previously-identified flags in an effort to improve the detection algorithm. The new detection models have shown accurate results exceeding 95 % for simplified screening scenarios 80-90 % when more realistic conditions are considered. [ABSTRACT FROM AUTHOR]

An associated particle neutron generator is described that employs a negative ion source to produce high neutron flux from a small source size. Negative ions produced in an rf-driven plasma source are extracted through a small aperture to form a beam which bombards a positively biased, high voltage target electrode. Electrons co-extracted with the negative ions are removed by a permanent magnet electron filter. The use of negative ions enables high neutron output (100% atomic ion beam), high quality imaging (small neutron source size), and reliable operation (no high voltage breakdowns). The neutron generator can operate in either pulsed or continuous-wave (cw) mode and has been demonstrated to produce 10 6 D–D n/s (equivalent to ~10 8 D–T n/s) from a 1 mm-diameter neutron source size to facilitate high fidelity associated particle imaging. [ABSTRACT FROM AUTHOR]

Highly explosive materials smuggled in sea land cargo containers are a security concern. An algorithm based on neutron and photon measurements during active neutron interrogation with 14.1 MeV neutrons was developed. The detection algorithm has now been evaluated for effectiveness over a wide range of explosive sizes, positions, and cargo configurations. Various sources of uncertainty were also studied. An estimate of the false positive and false negative rates was completed for various measurement conditions. Results showed that, although minimum detectable mass depends on the surrounding cargo, explosive position, and cargo configuration, 200 kg RDX could be reliably detected. [ABSTRACT FROM AUTHOR]

Fast neutron interrogation for explosives detection has shown potential for the screening of sea-land cargo containers. Simulations were completed investigating the neutron scatter behavior of 14.1 -MeV fast neutrons in such screening scenarios. Earlier efforts centered on Monte Carlo (MCNP5) simulations to identify flags or on specific calculations based on photons or neutrons produced as a result of fast neutron interaction that signal the presence of the explosive RDX (C2H6N6O6). Those simulations consisted of simplified target geometry; artificially collimated neutron source; and generalized organic, hydrogenous, or metallic types of cargo materials. In this study, the MCNP5 simulation was expanded to include a more accurate representation of the neutron source, target geometry, detector response, and realistic and varied container contents. The flags found using the earlier simulations were applied to the more realistic scenario models in order to determine the feasibility of the use of flags in a detection algorithm. Additional flags utilizing the simulated detector response were also investigated. The conditions under which specific flags were preferable were also examined. It was found that many flags performed well independent of the cargo type while others, such as those using only neutron backscatter, were more highly dependent on cargo type. Furthermore, many of the best-performing flags were those that did not require stringent neutron spectroscopy and would therefore be feasible with existing technology. [ABSTRACT FROM AUTHOR]

Radiological characterization of nuclear waste drums is an important task for the nuclear industry. The amount of actinides, such as ^235U or ^239Pu, contained in a package can be determined using non-destructive active methods based on the fission process. One of these techniques, known as neutron interrogation, uses a neutron beam to induce fission reactions on the actinides. Optimization of the neutron flux is an important step towards improving this technique. Electron accelerators enable to achieve higher neutron flux intensities than the ones delivered by deuterium-tritium generators traditionally used on neutron interrogation industrial facilities. In this paper, we design a neutron interrogation cell based on an electron accelerator by MCNPX simulation. We carry out photoneutron interrogation measurements on uranium samples placed at the center of 220 liter nuclear waste drums containing different types of matrices. We quantify impact of the matrix on the prompt neutron signal, on the ratio between the prompt and delayed neutron signals, and on the interrogative neutron half-life time. We also show that characteristics of the conversion target of the electron accelerator enable to improve significantly measurement performances. [ABSTRACT FROM PUBLISHER]

Abstract: The gamma-ray spectrum of spent nuclear fuel in the 3–6MeV energy range is important for active interrogation since gamma rays emitted from nuclear decay are not expected to interfere with measurements in this energy region. There is, unfortunately, a dearth of empirical measurements from spent nuclear fuel in this region. This work is an initial attempt to partially fill this gap by presenting an analysis of gamma-ray spectra collected from a set of spent nuclear fuel sources using a high-purity germanium detector array. This multi-crystal array possesses a large collection volume, providing high energy resolution up to 16MeV. The results of these measurements establish the continuum count-rate in the energy region between 3 and 6MeV. Also assessed is the potential for peaks from passive emissions to interfere with peak measurements resulting from active interrogation delayed emissions. As one of the first documented empirical measurements of passive emissions from spent fuel for energies above 3MeV, this work provides a foundation for active interrogation model validation and detector development. [Copyright &y& Elsevier]

Abstract: This paper presents the first application of a new technique for the measurement of the 235U content in fresh fuel assemblies. The technique, called time correlated induced fission (TCIF), uses a 252Cf neutron source to irradiate the fuel assembly, and the subsequent induced fission events in the fissile material are measured by multiplicity counting. The doubles and triples rates are enhanced by having the trigger events from both the 252Cf source and the induced fission neutrons in the same time gate in the coincidence analysis. The average neutrons per fission (ν) of the 252Cf source is 3.76 and the induced fission ν for 235U is 2.44, so the combined ν is ∼5.2 with one neutron removed by the fission reaction. This high effective ν significantly increases the multiplicity counting rates and reduces the statistical error. The background coincidence counts from the 252Cf have been minimized by neutron shielding between the source and the detector. This method of active neutron interrogation has been applied to the measurement of fresh pressurized water reactor (PWR) fuel assemblies. The neutron uranium collar (UNCL) that is routinely used for 235U verification in PWR reactor fuel assemblies is used to compare the TCIF method with the typically used AmLi neutron interrogation source. This paper presents both the experimental verification of the TCIF method for a PWR mockup assembly and the MCMPX simulations to optimize the detector geometry. [Copyright &y& Elsevier]

The solution for management of a nuclear waste package is chosen according to its radiological characteristics. One of the most important of these features is the \alpha-activity which is due to actinides (^235U, ^238U, ^239Pu, etc.) If non-destructive passive methods are not sufficient to quantify the latter, non-destructive active methods based on the fission process represent a solution of interest. First, these methods consist in irradiating a package in order to induce fission reactions on the actinides, and then, to detect the prompt and delayed particles which are emitted following these reactions. Our aim is to conduct neutron interrogation measurements on nuclear waste packages using an electron accelerator as a photoneutron generator. One of the main interests of this approach is that the intensity of the neutron flux can be one or two orders of magnitude higher than the one delivered by a deuterium-tritium generator. With the objective of improving nuclear waste characterization, the development of this method could enable the integration of three complementary techniques on a single measurement cell (active neutron interrogation, active photon interrogation, and high-energy imaging). In this paper, simulation and experimental results are presented. A simulation study using MCNPX has been conducted in order to determine the characteristics of the photoneutron flux emitted by the electron accelerator of the SAPHIR facility owned by CEA LIST. Energy spectra, angular distribution and intensity of the photoneutron flux have been obtained. A photoneutron interrogation measurement cell based on this accelerator has been built and assessed by carrying out measurements on uranium samples. Delayed gamma-ray spectra have been acquired and enabled to confirm the experimental feasibility of our method. [ABSTRACT FROM PUBLISHER]

In order to demonstrate the possibility of identifying the material within ship's underwater hull, sunken ships, or other objects on the sea floor, tests with a 14 MeV sealed tube neutron generator incorporated inside a small submarine were performed in the test basin filled with sea water. The results obtained for inspection of diesel fuel and explosive presence behind single and double hull structures are presented. [ABSTRACT FROM AUTHOR]

Abstract: A concept for detecting the presence of special nuclear material (235U or 239Pu) concealed in intermodal cargo containers has been developed, studied, and recent performance results are described. It is based on interrogation with a pulsed beam of 3–7MeV neutrons that produce fission events and subsequent detection of their β-delayed neutron emission or β-delayed high-energy γ-radiation reveals the presence of fissionable material. Fission product β-delayed γ-rays above 3MeV are nearly 10 times more abundant than β-delayed neutrons and are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified. Their impact on detection sensitivity is relatively minor and can be addressed readily. Components of a simple laboratory prototype have been assembled, tested with the most challenging cargo threat scenarios, and results compared to computer simulations. Preliminary results will be presented. [Copyright &y& Elsevier]

Abstract: A high-yield D–T neutron generator has been developed for neutron interrogation in homeland security applications such as cargo screening. The generator has been designed as a sealed tube with a performance goal of producing 5×1011 n/s over a long lifetime. The key generator components developed are a radio-frequency (RF) driven ion source and a beam-loaded neutron production target that can handle a beam power of 10kW. The ion source can provide a 100mA D+/T+ beam current with a high fraction of atomic species and can be pulsed up to frequencies of several kilohertz for pulsed neutron generator operation. Testing in D–D operation has been started. [Copyright &y& Elsevier]

Abstract: In recent years the detection and identification of hazardous materials has become increasingly important. This work discusses research and development of a technique which is capable of detecting and imaging hidden explosives. It is proposed to utilise neutron interrogation of the substances under investigation facilitating the detection of emitted gamma radiation and scattered neutrons. Pulsed fast neutron techniques are attractive because they can be used to determine the concentrations of the light elements (hydrogen, carbon, nitrogen, and oxygen) which can be the primary components of explosive materials. Using segmented High Purity Ge (HPGe) detectors and digital pulse processing [R.J. Cooper, G. Turk, A.J. Boston, H.C. Boston, J.R. Cresswell, A.R. Mather, P.J. Nolan, C.J. Hall, I. Lazarus, J. Simpson, A. Berry, T. Beveridge, J. Gillam, R.A. Lewis, in: Proceedings of the 7th International Conference on Position Sensitive Detectors, Nuclear Instruments and Methods A, in press; I. Lazarus, D.E. Appelbe, A. J. Boston, P.J. Coleman-Smith, J.R. Cresswell, M. Descovich, S.A.A. Gros, M. Lauer, J. Norman, C.J. Pearson, V.F.E. Pucknell, J.A. Sampson, G. Turk, J.J. Valiente-Dobón, IEEE Trans. Nucl. Sci., 51 (2004) 1353; R.J. Cooper, A.J. Boston, H.C. Boston, J.R. Cresswell, A.N. Grint, A.R. Mather, P.J. Nolan, D.P. Scraggs, G. Turk, C.J. Hall, I. Lazarus, A. Berry, T. Beveridge, J. Gillam, R.A. Lewis, in: Proceedings of the 11th International Symposium on Radiation Measurements and Application, 2006. ] the scatter path of incident photons can be reconstructed to determine the origin of the gamma-rays without the need for mechanical collimation by applying the Compton camera principle [V. Schonfelder, A. Hirner, K. Schneider, Nucl. Instr. and Meth. 107 (1973) 385; R.W. Todd, J.M. Nightingale, D.B. Everett, Nature 251 (1974) 132. ]. In addition, it is proposed to utilise the scattered neutrons which recoil from the materials being assayed, detecting them with a fast neutron detector providing data for inversion to tomographic images. In this paper, we present our approach to the design and implementation of a system for the efficient screening of goods in luggage and cargo containers. The simulation in a Monte Carlo framework using GEANT4 has been carried out for the imaging of gamma-ray events using the Compton camera design which will be discussed. The results of Compton camera measurements using HPGe detectors and the subsequent reconstructed images will also be presented. [Copyright &y& Elsevier]

To inspect cargo containers, X-ray imaging can be complemented by fast neutron interrogation to provide indication concerning the chemical nature of the transported goods through the detection of neutron-induced gamma rays. Organic goods are of special interest since they constitute a significant part of the merchandises. In addition, in the context of NRBC-E threats search in cargo containers, a nondestructive inspection system should also be able to detect explosives. Until now, fast neutron interrogation systems identify organic materials in cargo containers using characteristic neutron-induced gamma-ray peaks of carbon, oxygen and nitrogen. However, identifying organics in this way can lead to ambiguities, since no hydrogen gamma ray can be measured with fast neutrons. Nevertheless, it is known that hydrogen strongly modifies the neutron energy spectrum, which in turn affects the amplitudes of gamma-ray peaks. The link between the hydrogen fraction and the amplitude of gamma ray peaks being complex, no attempt has been made to inverse this link until now. Simulations show, however, that a neural network that takes as inputs the heights of carbon, oxygen and nitrogen gamma ray peaks can indeed determine the hydrogen fraction. Simulations of realistic cases show that the use of a neural network indeed allows identifying compounds having similar fractions of carbon, oxygen and nitrogen but different hydrogen fraction, thus opening the way to more accurate materials identification. • Hydrogen is measurable using gamma rays induced by fast neutrons on other nuclei. • A neural network can determine the hydrogen fraction in organic materials. • MCNP simulations validate the efficiency of the neural network approach. • Organic materials can be better discriminated. [ABSTRACT FROM AUTHOR]