American Journal of Modern Physics 2015; 4(5): 232-239 Published online August 27, 2015 (http://www.sciencepublishinggroup.com/j/ajmp) doi: 10.11648/j.ajmp.20150405.13 ISSN: 2326-8867 (Print); ISSN: 2326-8891 (Online) Characterization of Neutron Field in a Spherical Irradiation Facility M. Tohamy 1 , M. Fayez-Hassan 1 , S. Abd El-Ghany 2 , S. M. El-Minyawi 2 , M. M. Abd El-Khalik 1 , M. N. H. Comsan 1 1 Experimental Nuclear Physics Department, Nuclear Research Centre, Atomic Energy Authority, Cairo, Egypt, 2 Physics Department, Faculty of Science, Al-Azhar University (Girl's Branch), Cairo, Egypt Email address: Sahar_abdelghany@yahoo.com (S. Abd El-Ghany) To cite this article: M. Tohamy, M. Fayez-Hassan, S. Abd El-Ghany, S. M. El-Minyawi, M. M. Abd El-Khalik, M. N. H. Comsan. Characterization of Neutron Field in a Spherical Irradiation Facility. American Journal of Modern Physics. Vol. 4, No. 5, 2015, pp. 232-239. doi: 10.11648/j.ajmp.20150405.13 Abstract: A small-sized dual-hemisphere irradiation facility designed and constructed for using Am-Be isotopic neutron source to study and characterize the neutron field around sample irradiation position for obtaining maximum thermal neutron flux. The foil activation method based on 115 In and 197 Au was used for monitoring the thermal neutron flux. For field characterization, several combinations of moderation media have been tested (air, sand and water) aiming at the identification of the best combinational setups for sample irradiations using thermal neutrons. To account for epithermal contribution, reaction rates and flux calculations were corrected using tabulated values of Westcott g-factors and resonance integrals for these media. The optimal position for sample irradiation using thermal neutron for both water-water and water-sand setups, inside the irradiation channel, was found at about 6.9 to 10.9 cm from the center of the neutron source. Keywords: Irradiation Facility, Am-Be Neutron Source, Source Shielding, Neutron House 1. Introduction The neutron activation analysis (NAA) method is considered one of the most famous methods to investigate elements in a variety of sample matrices. In the NAA the sample to be analyzed is exposed to a thermal neutron flux; then, the induced activity of the sample is measured using absolute or comparative method. For this purpose a previously described small-sized neutron irradiator prototype based on a 5 Ci (1.85×10 11 Bq) Am-Be isotopic neutron source was prepared [1]. The use of the neutron irradiator presents the advantage of supplying a stable neutron flux over a long period [2-4], thus eliminating the need for using expensive neutron producing devices such as reactors or accelerators. This way makes the analyzing process became agile, practical and economic. This work presents the optimization of the neutron irradiator for thermal and epithermal neutron production using several combinations of moderating media. 2. Experimental Facility Description In this work, the neutron irradiation facility designed and constructed previously in the shape of a spherical container was used [1]. The design aimed to achieve symmetry with respect to the position of the neutron source used at the center of the sphere. The facility was designed for the accommodation and safe-handling of the 5 Ci Am-Be isotopic neutron source. The neutron irradiator consists of a sphere of 60 cm in diameter made of a galvanized steel sheet and divided to two hemispheres. The lower hemisphere is an open to be used as container to be filled with different media. The upper hemisphere has a sealed bottom with embedded-in horizontal tube used to place the neutron source at the center of the sphere. Moreover, within the upper hemisphere a vertical cylindrical tube of 3.2 cm diameter was welded at the top of it and at the mid place of the source containing horizontal tube. The vertical tube is a devoted space for sample’s irradiation, and contains equally spaced holes of appropriate diameter to allow water or air to achieve homogeneous medium in the upper hemisphere. The source contained in a stainless steel tube can be moved in the horizontal direction and its position is determined by the neutron source handling system. The experimental arrangement of the facility including the neutron irradiator,