7905

7353

كارشناسي ارشد

فيزيك هسته اي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1391

هشت،76ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

احمد شيراني

مجيد جلالي

4/6/92

محمد حسن علامت ساز، مريم حسنوند

فيزيك

ID7353

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Desinging an optimum shield for Am Be neutron source for detection of explosive materials by PGNAA method Sayedeh Hamideh Kanani Hamidekanani@gmail com Date of Submission January 16 2013 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr A Shirani Email shirani@cc iut ac ir Abstract Prompt gamma neutron activation analysis PGNAA is a nondestructive nuclear method for detection of various elements present in a material sample In this method the sample is irradiated by neutrons The neutrons are absorbed by the target nuclei with different proabilities and compound nucleus is formed The conpound nucleus then emits prompt gamma ray within second These prompt gamma rays are characteristic of the elements present in the sample So by detecting and analysing these gamma rays we can determine the type and amount of the elements present in the sample Instruments needed for this analysis are neutron source sample gamma detector gamma and neutron sheilds The purpose of this thesis is desiging a proper shield and a proper moderator with optimum thicknesses and materials for the Am Be neutron source to detect prompt gamma rays emitted from nitrogen present in explosive materials The Am Be source emits a 4 43 MeV gamma ray resulted from the decay of exited carbon and the mean energy of neutrons emitted from this source is 4 4 MeV The optimum sheild for this source increases the PGNAA efficiancy by decreasing the pile up due to source gamma and increasing the thermal nutron flux in the sample So at first step we assumumed a cylinder lead shield around the source and calculated the optimum thickness for the shield by simulation The optimum thickness was found to be 5cm which decreases source gamma ray by 90 but due to lab facilities limitations we could use a cylinder lead shield with a thickness of 3 5cm which attenuates the source gamma ray to about 70 Explosive materials contain nitrogen absorbs thermal neutrons with 0 75 barn of crossection and emits a 10 83 MeV prompt gamma ray For increasing the thermal neutron in the sample three types of moderators water polyethelen and graphite with different thicknesses were simulated and for each type optimum thickness was found The optimum thickness of water and polyethelen is 3cm and for graphit is 15cm After that we used a graphite refelector around the source for increasing the neutron flux in the sample Finally for verifing the simulations two experiments were done The lab conditions were simulated and the optimum thickness of water was determined 2cm with polyethylene container So experiments were done for optimum thickness and for 5cm thickness for examining the more water thickness The experimental result is compatible with simulation result So we can say that the designed system in terms of shield and moderator of source has optimum condition in order to detect explosive materials Keywords 1 Prompt gamma neutron activation analysis 2 PGNAA 3 Explosive detection 4 Am Be neutron source PDF created with pdfFactory trial version www pdffactory com

احمد شيراني

مجيد جلالي

محمد حسن علامت ساز، مريم حسنوند