Akademik Veri Yönetim Sistemi
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, cilt.338, ss.139-144, 2014 (SCI-Expanded)
For the applicability of instrumental neutron activation analysis (NAA) technique, an irradiation unit with a 37 GBq(241) Am-Be neutron source was installed at Institute of Nuclear Sciences of Ankara University. Design and configuration properties of the irradiation unit are described. It has two different sample irradiation positions, one is called site #1 having a pneumatic sample transfer system and the other is site #2 having a location for manual use. In order to characterize neutron flux spectra in the irradiation sites, the measurement results were obtained for thermal (phi(th)) and epithermal neutron fluxes (phi(epi)), thermal to epithermal flux ratio (f) and epithermal spectrum shaping factors (alpha) by employing cadmium ratios of gold (Au) and molybdenum (Mo) monitors. The activities produced in these foils were measured by using a p-type, 44.8% relative efficiency HPGe well detector. For the measured gamma-rays, self-absorption and true coincidence summing effects were taken into account. Additionally, thermal neutron self-shielding and resonance neutron self-shielding effects were taken into account in the measured results. For characterization of site #1, the required parameters were found to be phi(th) = (2.11 +/- 0.05) x 10(3) n cm(-2) s(-1), (phi(epi) =(3.32 +/- 0.17) x 10(1) n cm(-2) s(-1), f = 63.6 +/- 1.5, alpha = 0.045 +/- 0.009, respectively. Similarly, those parameters were measured in site #2 as phi(th) =(1.49 +/- 0.04) x 10(3) n cm(-2) S-1, phi(epi) = (2.93 +/- 0.15) x 10(1) n cm(-2) s(-1), f = 50.9 +/- 1.3 and alpha = 0.038 +/- 0.008. The results for f-values indicate that good thermalization of fast neutrons on the order of 98% was achieved in both sample irradiation sites. This is because an optimum combination of water and paraffin moderator is used in the present configuration. In addition, the shielding requirements are met by using natural boron oxide powder (5.5 cm) and boron loaded paraffin layers against neutrons, and a 15 cm thick lead bricks against gamma-rays from source and its surrounding materials. (C) 2014 Elsevier B.V. All rights reserved.