Tagged Neutron Method Research Articles

Experiment and MCNP simulation of a portable tagged neutron inspection system for detection of explosives in a concrete wall

Abstract The Tagged Neutron Method (TNM) widely used in recent years has been applied to detect explosives to fight against terrorism. Because of the existence of a high-density (about 2.5 g/cm3) dry concrete wall, neutrons are moderated and γ -ray are attenuated and absorbed, which causes great interference to the detection of hidden explosives. A movable device has been designed for detection of explosive embedded in a concrete wall by using TNM technique. The experimental set-up was modeled and optimized with the MCNP5 Monte Carlo code. The γ -ray energy spectrum of graphite sample was firstly collected to calibrate the detection system and verify the validity of the MCNP5 model. Then γ -ray energy spectra of different samples under different situation are accumulated and compared with the simulation results. The samples of TNT and ammonium nitrate surrogate were placed behind a concrete wall with thickness of 10 cm, 15 cm and 20 cm, respectively. The comparison of the MCNP simulation results with experiment is in a good agreement. The results obtained provide a good reference for the subsequent data acquisition and analysis by using this model.

Modeling of tagged neutron method for explosive detection using GEANT4

The study has been focused on modeling the capabilities of tagged neutron method (TNM) for detection and identification of explosive materials using an approximated experimental configuration. The underlying principle is to use D-T (14.1 MeV) neutrons tagged by its associated charged particle and incorporating neutron time-of-flight technique to identify explosives by estimating carbon, nitrogen and oxygen contents and their ratios. This research was carried out to facilitate the design and construction of a prototype laboratory based TNM system and a simulation model was developed in the GEANT4 framework. The model has established an environment for (a) simulating production of D-T tagged neutrons, their transport and interactions with an object to induce emission, detection of characteristic gamma-rays and (b) image reconstruction (3D) of the interrogated object using time-of-flight information of neutron and gamma-ray. The geometrical configuration includes 14.1 MeV tagged neutrons, a position sensitive alpha detector and an array of BGO (3” x 3”) gamma detectors arranged in a square geometry around the sample to collect the neutron induced gamma-ray spectra. With this configuration of tagged neutron system, a reference data set of pure elements’ (C, O, N, Al and Fe) neutron induced gamma energy spectra was generated. Simulated spectra of benign (urea, melamine) and explosive (RDX, TNT, ammonium nitrate) samples were analyzed and their elemental compositions of C, N and O were extracted with linear combination of reference data set. The resulting compositions were found to be close to the actual values. Further, the effects of the matrix materials on energy spectra of sample were studied with explosive (1 kg RDX) hidden inside a small container filled with (1) metallic matrix composed of iron (56Fe) or (2) organic matrix (C2.59H5.05N0.55O1.6) with an average densities of 0.1, 0.2 g/cc. Simulation results have shown the system’s capability in detecting and imaging of hidden explosives (1 kg RDX) within a metallic matrix is better than that in a wood matrix.

Measurement of Angular Distributions of Gamma Rays from the Inelastic Scattering of 14.1-MeV Neutrons by Carbon and Oxygen Nuclei

The results obtained by measuring the angular and energy distributions of gamma rays originating from the inelastic scattering of 14.1-MeV neutrons by carbon and oxygen nuclei are presented. The measurements in question were performed by the tagged-neutron method in a beam of an ING-27 standard portable neutron generator. The angular distributions of gamma rays emitted by the 2+ state of 12С at 4.43 MeVand the 3− state of 16O at 6.13 MeV were obtained.

Measurements of the gamma-quanta angular distributions emitted from neutron inelastic scattering on 28Si

The characteristic gamma radiation from the interaction of 14.1 MeV neutrons with a natural silicon sample is investigated with Tagged Neutron Method (TNM). The anisotropy of gamma-ray emission of 1.779 MeV was measured at 11 azimuth angles with a step of ∠15°. The present results are in good agreement with some recent experimental data.

Detection of diamonds in kimberlite by the tagged neutron method

A new technology for diamond detection in kimberlite based on the tagged neutron method is proposed. The results of experimental researches on irradiation of kimberlite samples with 14.1-MeV tagged neutrons are discussed. The source of the tagged neutron flux is a portable neutron generator with a built-in 64-pixel silicon alpha-detector with double-sided stripped readout. Characteristic gamma rays resulting from inelastic neutron scattering on nuclei of elements included in the composition of kimberlite are registered by six gamma-detectors based on BGO crystals. The criterion for diamond presence in kimberlite is an increased carbon concentration within a certain volume of the kimberlite sample.

Parameters of explosives detection through tagged neutron method

The potentialities of tagged neutron method (TNM) for explosives detection are examined on the basis of an idealized geometrical model. The model includes ING-27 14MeV neutron generator with a built-in α-detector, a LYSO γ-detector and samples of material to be identified of approximately 0.3kg each: explosives imitators (trinitrotoluene - TNT, tetryl, RDX and ammonium nitrate), legal materials (sugar, water, silk and polyethylene). The samples were unshielded or shielded by a paper layer of various thicknesses.The experimental data were interpreted by numerical simulation using a Poisson distribution of signals with the statistical parameters defined experimentally. The detection parameters were obtained by a pattern classification theory and a Bayes classifier.

Stationary setup for identifying explosives using the tagged neutron method

The results of using a stationary setup for detecting and identifying explosives using the tagged neutron method (or associated particle imaging (API) method) have been presented. The source of 14.1-MeV tagged neutron beams is an ING-27 portable neutron generator made by VNIIA (Moscow). It contains an embedded 64-pixel silicon α detector with double-sided strip readout developed by the Joint Institute for Nuclear Research (JINR). The setup was tested for the identification of more than 30 explosives.