Author's personal copy Investigations of shield effect and type of soil on landmine detection Nassreldeen Elsheikh a,n , Farouk Habbani b , Ibrahim ElAgib a,c a College of Applied & Industrial Science, Department of Physics, University of Juba, Khartoum, P.O. Box 12327/1, Sudan b Faculty of Science, Physics Department, University of Khartoum, Khartoum, P.O. Box 321, Sudan c College of Science, King Saud University, P.O. Box 2455, Saudi Arabia article info Available online 20 May 2011 Keywords: Landmine detection Shield effect Soil type abstract This paper investigates the possibility of optimizing the performance of the neutron backscattering method in landmine detection by designing a suitable shield around a 252 Cf neutron source to reduce the background due to soil and the neutrons emitted from the source that hit the detector directly. A series of Monte Carlo simulations were performed to improve the source shield thickness and to study the elastically backscattered (EBS) 252 Cf neutrons from the buried explosive material TNT in the soil; the optimal configuration was examined against different soil types and source heights. The results obtained in terms of performance of the relative (EBS) neutrons confirmed that the proposed source shield has significantly improved the signal to background ratio. Higher signal-to-background ratio was observed using 252 Cf neutron source as compared to Pu–Be source. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Landmines present physical and psychological threats to communities: they inhibit agricultural production, food security, economic activity and freedom of movement. Therefore it is highly significant to review the techniques available in use for landmine detection and propose the most simple and straightfor- ward method. The most common explosives used in landmines are TNT (C7H5N3O6) and RDX (C3H6N6O6). The anti-personnel landmines are usually designed in the form of a disk or a cylinder, with diameters from 20 to 125 mm, lengths from 50 to 100 mm, mass as little as 30 g and are usually shallow-buried [1]. Several landmine detection methods, based on nuclear techniques, have been suggested in recent years, including neutron energy mod- eration, neutron-induced gamma emission, neutron and gamma attenuation, and slow and fast neutron backscattering [1–6]. Neutron backscattering technique has successfully been applied to the detection of non-metallic landmines buried in relatively dry sandy soil. Fast neutrons from a radio-isotopic source are moderated and backscattered more by the buried landmines than the surrounding soil [2]. The number of slow neutrons that are reflected from the soil is a direct indication of the amount of hydrogen. In most cases, the amount of hydrogen in a plastic landmine is much higher than that of the surrounding soil. Therefore, if an appropriate neutron detector in combination with a neutron source is used to scan across the soil, the presence of a landmine will be indicated by an increase in the count rate. Also, the elastic scattering cross-sections have been shown to be much higher than the inelastic, or radiative capture ones [5]. Conse- quently, in order to use a source of modest strength in a radiologically acceptable portable device, it is sensible to devise a detection system that relies on elastic scattering of neutrons. A landmine can be detected only if the net signal due to the hidden explosive is significantly higher with respect to the back- ground due to the soil and the neutrons emitted from the source that hit the detector directly [7]. Therefore, in order to optimize the final performance of the EBS neutrons method and conse- quently improve the population of neutrons contributing to landmine detection, the background needs to be effectively minimized by the proper selection of a source–sample–detector geometry and an effective shield around a suitable neutron source. The present work investigates such a possibility. The possibility of using polyethylene (PE) and borated complexes as shielding materials was investigated [8]. The investigations con- firmed that the presence of 10 B in borated complexes makes them suitable absorbers of thermal neutrons and the presence of 1 H in hydrogenous materials such as PE makes them suitable modera- tors. Such a system for neutron source shield will increase signal- to-background ratio and thus facilitate the landmine detection process. On the basis of such considerations, Monte Carlo simula- tions were carried out to investigate the feasibility of using a neutron shield consisting of two layers: high density polyethylene (PE) and 5% borated polyethylene (BPE) as the first and second layer, respectively. The results were obtained in terms of varia- tions in the signal-to-background ratio (S/B) due to changes in soil type, source position and type of source. The signal-to-background Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.09.183 n Corresponding author. Tel.: þ24 9906082101; fax: þ249 9183222142. E-mail address: nassreldeen.elsheikh@yahoo.com (N. Elsheikh). Nuclear Instruments and Methods in Physics Research A 652 (2011) 1–4