Calculation of Thermal Neutron Absorption in Cylindrical and Spherical Neutron Sources

Abstract

A calculation of the thermal neutron self-absorption for cylindrical or spherical neutron sources has been made. The calculations are confirmed by the experimentally-measured difference in manganous sulfate bath activity for bare and cadmium-covered Pu-Be and Am-Be neutron sources. The calculation is done in single interaction approximation and assumes that the incident thermal neutron flux is isotropic. The source material may be fissionable and be covered by up to three cladding materials. A computer program has been written for the numerical calculations.

NEUTRON SOURCES AND APPLICATIONS. Proceedings of the American Nuclear Society National Topical Meeting, April 19--21, 1971, Augusta, Georgia. Sessions I and II.

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“…The Mobile Nondestructive Assay Laboratory's 200 keV accelerator plus necessary support equipment and the shielded experimental cavity where neutron interrogation is carried out, have beendescribed (3). Figure 1 shows the exterior of the 10 x Soft.…”

“…The manufacturer advises that a factor of three increase can 'be obtained by increasing the specific activity of the microspheres and that art additional factor of three can be achied;ed by the elimination o f dilution of the microspheres by inert material (3). A d!nser packing of the spheres on the souice surface may result in a further increase s by a factor of 3-4.…”

“…A recent calculation and experimental verification of neutron ab-C(>NTRSBUTION Obr THE NATIONAL BUREAU OF STANDARDS NOT SUBJECT TO COPYRIGHT sorption in /;he source itself (2,3) removes the :Limitation of this To?-rection to tl;lin sources only. Briefly, the calcylation I s applicable to sources of ail1 ranges of absorption or fission c:ross section and encapsulations o f / any 3 materials.…”

“…of neutrons, high LET secondary r a d i a t i o n can be delivered t o a t a r g e t volume i n the treatment of a malignant tumor. Q u a l i t a t i v e l y d i f f e r e n t r e s u l t s i n the c l i n i c may emerge because o f p o s s i b l e advantages of californium neutrons : ( 1 ) t h e e q u a l i z a t i o n of d i f f e r e n t i a l i n s e n s i t i v i t y of c e l l s due t o t h e i r oxygenated s t a t e ; (2) a higher r e l a t i v e b i o l o g i c a l e f f e c t i v e n e s s c l o s e t o t h e sources with a decreasing e f f e c t i v e n e s s with distance from t h e source; (3) an apparent absence of dose r a t e e f f e c t s at neutron dose rates < 50 rads/ hr. In order t o obtain any r e s u l t s , regardl e s s of t h e i r b a s i s or q u a l i t y , a method i s necessary f o r evaluation of the treatment dose from t h e r a d i a t i o n delivered by a californium implant.…”