The relationship of sample mass to thermal neutron self shielding factor for a finite cylinder sample geometry irradiated in an isotropic neutron field

THE RELATIONSHIP OF SAMPLE MASS TO THERMAL NEUTRON SELF SHIELDING FACTOR FOR A FINITE CYLINDER SAMPLE GEOMETRY IRRADIATED IN AN ISOTROPIC NEUTRON FIELD ( M. Sc. Thesis) Mustafa Güray BUDAK GAZİ UNIVERSITY INSTITUTE OF SCD2NCE AND TECHNOLOGY AUGUST 2002 ABSTRACT The neutron self-shielding of samples against thermal neutrons may occur substantially during neutron irradiations of relatively large amounts of elements with very high neutron absorption cross sections. Therefore, the use of neutron activation analysis to obtain accurate analytical results requires that neutron self-shielding effects be eliminated or corrected. Since the self-shielding correction factors for thermal and epithermal neutrons depend on various physical and nuclear parameters; they must be calculated for different sample geometries such as slab, sphere, cylinder etc. in both isotropic and beam neutron fields, using suitable models. An experimental study of thermal neutron self-shielding of the finely grained indium oxides ranging in large amounts from 0,2 to 2,2 g for a finite cylinder sample geometry in an isotropic neutron field has been made by activation technique. The induced specific activities of indium with a 1 mm-thick Cd shield case and without Cd were measured in a high pure Ge detector. From the measured results, a relationship between sample mass and thermal neutron self-shieldind factor for a finite cylinder geometry of sample for the case of isotropic neutron field is proposed. The obtained empirical relationship is in good agreement with the experimental results. The relationship, which depends on the sample mass and the macroscopic total cross section in a given size of a finite cylinder, is also applicable for various materials with different absorption cross sections for the same sample geometry for the case of isotropic neutron irradiation. Science code : 404.04.01 Key words : Thermal neutron, self-shielding, correction factor, neutron activation, indium, isotropic neutron field Page number : 81 Adviser : Assoc. Prof. Dr. Haluk YÜCEL