We present status of simulations used to design a novel device for the
detection of hazardous substances in the aquatic environment using neutron
activation. Unlike the other considered methods based on this technique we
propose to use guides for neutron and gamma quanta which speeds up and
simplifies identification. First preliminary results show that both the neutron
guide and the $\gamma$ ray guide increase the performance of underwater threats
detection.Comment: Presented at the Jagiellonian Symposium of Fundamental and Applied
  Subatomic Physics, Krak{\o}w, 11.06.201

Hunik, D

Moskal, P

Silarski, M

Smolis, M

Tadeja, S

Acta Physica Polonica B

English

arXiv

We present status of simulations used to design a novel device for the detection of hazardous substances in the aquatic environment using neutron activation. Unlike the other considered methods based on this technique, we propose to use guides for neutron and gamma quanta which speeds up and simplifies identification. First preliminary results show that both the neutron guide and the $\gamma$-ray guide increase the performance of underwater threats detection

Silarski, Michał

Hunik-Kostyra, Dominika

Smolis, Michał

Tadeja, Sławomir

Moskal, Paweł

Jagiellonian Univeristy Repository

Vol. 47 (2016) ACTA PHYSICA POLONICA B No 2DESIGN OF THE SABAT SYSTEM FOR UNDERWATERDETECTION OF DANGEROUS SUBSTANCESM. Silarski, D. Hunik, M. Smolis, S. Tadeja, P. MoskalThe Marian Smoluchowski Institute of Physics, Jagiellonian UniversityŁojasiewicza 11, 30-348 Kraków, Poland(Received January 28, 2016)We present status of simulations used to design a novel device for thedetection of hazardous substances in the aquatic environment using neutronactivation. Unlike the other considered methods based on this technique,we propose to use guides for neutron and gamma quanta which speeds upand simplifies identification. First preliminary results show that both theneutron guide and the γ-ray guide increase the performance of underwaterthreats detection.DOI:10.5506/APhysPolB.47.4971. IntroductionGrowing risk of terrorism demands a constant development of new tech-niques for hazardous substances detection. One of the best methods forhomeland security are based on the Neutron Activation Analysis (NAA) pro-viding non-intrusive detection of explosives or drugs. The principle of themethod is to use a fast neutron beam produced using sealed D+T generatorto excite nuclei of investigated substance and detect characteristic gammaquanta produced in de-excitation of the nuclei. This allows one to identifythe stoichiometry of the substance and determine if it is dangerous [1, 2].So far, there are several devices based on the Neutron Activation Analysisdesigned for ground homeland security which were introduced in the USA byScience Applications International Corporation [3] and CALSEC [4], and inEurope in Sodern [5], EURITRACK [6] and SWAN [7] projects. These de-vices are used in the homeland security or contraband detection on the land.However, in an aquatic environment, one encounters serious problems due tostrong attenuation of neutrons in water. Moreover, as in the case of grounddetectors, an isotropic generation of neutrons induces a large environmentalbackground. This noise can be significantly reduced by the requirement ofthe coincident detection of the alpha particles which are produced together(497)498 M. Silarski et al.with neutrons [8, 9]. The attenuation of neutrons can be compensated byreducing the distance between generator and examined item [10]. There arealso solutions based on low-energy neutrons which are moderated in wa-ter before reaching the tested object. The detector is then counting thegamma quanta from thermal neutron capture and secondary neutrons orig-inating from the irradiated object. The identification is done by searchingfor anomalies in the observed spectra of gamma quanta and neutrons [11].However, these methods do not allow to detect explosives buried deeper inthe bottom of the sea and strong attenuation of neutrons and gamma quantasignificantly increases the exposure time.An alternative solution of a detector which uses the NAA technique andspecial guides for neutrons and emitted gamma rays was proposed withinthe SABAT project [12]. The device allows for detection of dangerous sub-stances hidden deep in the bottom of the sea with significantly reducedbackground and provides determination of the density distribution of thedangerous substance in the tested object [11]. In this article, we present sta-tus of the design of the SABAT detector based on Monte Carlo simulations,focusing on the impact of the usage of neutron and gamma quanta guides.2. Status of the simulationIn order to optimize the dimensions and relative positions of detectorsand guides, we have developed dedicated open source software package writ-ten in the C++ programming language [11]. This simulation tool is usingnovel methods of geometry definition and particle tracking, and the OpenMPI library supporting parallel computing [13]. To define the geometry ofsimulated objects, we use a polygon mesh, which is, in the simplest form,a collection of vertices and edges that are used to define a surface of thepolyhedral 3D object. In our case, the faces consist of triangles. A trajec-tory of a particle traveling in a scene consisting of such defined objects issimulated with the so-called ray tracing technique. To determine if a parti-cle entered the given object, the Möller–Trumbore method was implementedwhich searches for intersection of the particle trajectory with the object sur-face (triangle mesh). The total cross sections and angular distributions ofneutrons and γ-rays interaction with selected nuclei were parametrized as afunction of energy using data from the Evaluated Nuclear Data File (ENDF)database [14], while gamma quanta energies were taken from the EvaluatedNuclear Structure Data Files (ENSDF) [15]. As a starting point for design ofthe device for underwater threats detection, we have defined a simple setupwith point-like source generating uniformly in space of 14.1 MeV neutrons inthe neutron-α center-of-mass frame. As a first step, to study the influenceon the measurement of gamma quanta guide and the relative position of gen-Design of the SABAT System for Underwater Detection of Dangerous . . . 499erator and detector, we have simulated 1.4 × 107 events with two differentdetector locations with and without gamma-rays guide. The scheme of thesimulated setups with superimposed γ quanta interaction points are shownin Fig. 1. The interrogated object with dimensions 194 × 50 × 50 cm3 liesat the bottom of a sea and contains mustard gas (C4H8Cl2S). The neutronguide is a cuboid with dimensions 40 × 100 × 40 cm3, while gamma-raysFig. 1. (Color on-line) Distribution of γ quanta interaction points in x–y views fortwo positions of the detector with ((a) and (b)) and without gamma quanta guide((c) and (d)). The point-like source of neutrons is located at the origin of thereference frame. The neutron guide is presented as the blue dashed rectanglealigned along the y axis. The container with mustard gas is a red cuboid alignedhorizontally which lies at the bottom of the sea marked in cyan. The Ge detector(black/yellow) is connected to the gamma rays guide (dashed magenta polyhedron).For better visibility of the influence of guides plots are made only for −10≤ z ≤10 cm.500 M. Silarski et al.guides are represented by polyhedron with 15 × 20 cm2 and 30 × 30 cm2bases. They are both filled with air under normal conditions. As a detec-tor, we have simulated 15× 15× 20 cm3 Ge crystal measuring the energy ofgamma rays with 6% resolution (FWHM). The detector surface with dimen-sions of 15 × 20 cm2 is adjusted to the shape of the gamma quanta guide.The exemplary energy spectra measured by the germanium detector for onedetector position are shown in Fig. 2. As one can see in Table I, amongall of the gamma quanta reaching the detector, about 80% originate fromoxygen in the water independently of the detector position or presence of theguide. The second relevant source of background constitute neutrons whichscatter in water and reach the detector. The amount of registered gammaquanta which were created in the container with mustard gas is quite smallbut the advantage of using guide is visible. The mustard gas is composedof carbon, hydrogen, chlorine and sulfur. However, Fig. 2 indicates that the4.4 MeV carbon line is overwhelmed by background, while we see clearlygamma quanta from carbon with energy of about 9.6 MeV. In the case ofchlorine and sulfur (lines of 6.5 MeV and 2.2 MeV, respectively), the oxygenbackground has to be significantly reduced to allow one to identify theseelements more clearly. This can be done requiring the coincident detectionof the α particle generated together with neutron or by covering all theFig. 2. Simulated energy spectra as would be measured with the germanium de-tector. Simulations were performed for the setups presented in Fig. 1 (b) (solidhistogram) and in Fig. 1 (d) (dashed histogram). The small signal from the mus-tard gas can be seen at about 9.6 MeV and 4.4 MeV (carbon), 2.2 MeV (sulfur)and around 6.5 MeV (chlorine). The huge background is mainly due to the gammaquanta from neutron-oxygen reactions. The energy of these quanta is smeared dueto the scattering in the water. The number of entries is normalized to the generatedstatistics.Design of the SABAT System for Underwater Detection of Dangerous . . . 501TABLE IFractional composition of sources of gamma quanta registered by the detector(in %) for all the simulated cases shown in Fig. 1. The last column shows theoverall fraction of gamma quanta reaching the detector and originating from themustard gas.Setup H C N O Na Si S Cl n Mustardgasa 0 0.77 0 85.17 0.24 0 0 0.26 13.56 1.02b 0.53 1.68 0.10 76.50 0.38 0.08 0.63 1.78 18.32 3.30c 0.59 0 0 81.71 0.88 0 0 0.89 15.93 0d 7.88 0.59 0.05 77.04 0.69 0.24 0.10 6.95 6.46 2.25detector faces not connected to the gamma quanta guide with thick layerof absorber. Identification of sulfur and chlorine is difficult due to neutroncapture on hydrogen giving lines of very close energy and chlorine content inthe sea water [11]. However, using the gamma quanta guide, one can detectγ rays from these two elements not affected by scattering in the water whichgives a great advantage in the identification.3. Conclusions and outlookIn the framework of the SABAT project, we have been developing sim-ulation package based on novel methods of geometry definition and particletracking. Although we are still in a very early stage of development, thefirst results indicate that indeed, both the neutron guide and γ-ray guidewill increase the performance of underwater threats detection with fast neu-trons [11]. With 1.4× 107 generated neutrons, we see enhancements of sig-nal events in the detector together with huge background originating mostlyfrom oxygen, as it was expected. This shows clearly that all the faces ofthe detector not connected to the guide should be covered with thick layerof material absorbing γ quanta and neutrons which constitute another bigsource of background. This noise can be also significantly reduced by therequirement of the coincident detection of the α particle generated togetherwith neutron, which allows for the neutron tagging [11]. As one of the possi-ble way of the background suppression via time-of-flight method, we consideran application of plastic scintillators in order to take advantage of their ex-cellent timing properties, as recently demonstrated in the case of low-energygamma quanta [16–20]. The α-particle detection and time measurement willbe included as the next step in the development of the simulations. Thiswill allow for a final design of the device for underwater threats detectionwith fast neutrons, which requires much bigger statistics generated.502 M. Silarski et al.REFERENCES[1] P. Moskal, Ann. UMCS, Sect. Phys. 66, 71 (2011).[2] M. Silarski, Acta Phys. Pol. B Proc. Suppl. 6, 1061 (2013).[3] http://phoenixnuclearlabs.com/solution/explosives-detection/[4] B.C. Maglich, AIP Conf. Proc. 796, 431 (2005); http://www.calseco.com/[5] http://www.sodern.com/[6] http://www.euritrack.org/[7] Ł. Kaźmierczak et al., Acta Phys. Pol. A 127, 1540 (2015);http://aid.ncbj.gov.pl/index.php/en/products/swan[8] D. Sudac et al., Nucl. Instrum. Methods B 261, 321 (2007).[9] S. Pesente, Ph.D. Thesis, University of Padova, 2003.[10] C. Eleon et al., Nucl. Instrum. Methods A 629, 220 (2011).[11] M. Silarski et al., Acta Phys. Pol. A 127, 1543 (2015).[12] M. Silarski, P. Moskal, International patent applicationNo. PCT/PL2015/050021.[13] M.J. Quinn, Parallel Programming in C with MPI and OpenMP,McGraw-Hill, 2004.[14] M.B. Chadwick et al., Nucl. Data Sheets 112, 2887 (2011).[15] M.R. Bhat, Nuclear Data for Science and Technology (revised as of April2014) Ed. S.M. Qaim, Springer-Verlag, Berlin, Germany, 1992.[16] L. Raczyński et al., Nucl. Instrum. Methods A 764, 186 (2014).[17] P. Moskal et al., Nucl. Instrum. Methods A 764, 317 (2014).[18] L. Raczyński et al., Nucl. Instrum. Methods A 786, 105 (2015).[19] P. Moskal et al., Nucl. Instrum. Methods A 775, 54 (2015).[20] P. Moskal et al., Phys. Med. Biol. 61, 2025 (2016).

Design of the SABAT system for underwater detection of dangerous substances

M. Silarski

D. Hunik

M. Smolis

S. Tadeja

P. Moskal

Crossref

Design of the SABAT System for Underwater Detection of Dangerous Substances

We present status of simulations used to design a novel device for the detection of hazardous substances in the aquatic environment using neutron activation. Unlike the other considered methods based on this technique we propose to use guides for neutron and gamma quanta which speeds up and simplifies identification. First preliminary results show that both the neutron guide and the $\gamma$ ray guide increase the performance of underwater threats detection

CUED - Cambridge University Engineering Department

Design of the SABAT system for underwater detection of dangerous
  substances

Design of the SABAT system for underwater detection of dangerous substances

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CUED - Cambridge University Engineering Department