Gamma Rays Associated With Fission

Abstract

I. INTRODUC'ITON Although many properties of the f i s s i o n fragments and fast neutrons from U-235 f i s s i o n have been measured i n d e t a i l (l) , corresponding studies f o r fission-associated gamma radiation have not been reported. describes experiments designed t o determine as a function of time after f i s s i o n t h e absolute energy spectra of the gamma radiation emitted with the thermal f i s s i o n of U-235*. This paper The energy release i n the form of gamma radiation from U-235 fission, (1 3. 1 + 1. 3) MeV per f i s s i o n , represents a significant f r a c t i o n (about 6$) of t h e t o k energy release per fission. Moreover, of t h e f i s s i o n radiations, only neutrons compete with gamma, rays f o r the position of greatest importance t o the design of nuclear reactor shields (2). In order t o design an e f f i c i e n t reactor shield, the absolute energy spectrum of the emitted gamma radiation must be known, since t h e cross sections pertinent t o the attenuation processes are strongly energy dependent. For a shut-dam reactor or f o r used reactor f i e l , the shielding requirements are determined almost e n t i r e l y by the presence of gamma rays emitted by the radioactive f i s s i o n products. An additional. reactor-design problem i s the removal of heat produced by gamma-ray interactions both in the reactor core and i n the surrounding regions. pressure shell, and shield regions of a reactor, and f o r experimental apparatus used with r e s e a x h reactors. Efficient design of these cooling systems i s dependent upon a knowledge of t h e energy spectra of the sources of gamma radiation associated with f i s s i o n (3). Special cooling systems must frequently be provided f o r r e f l e c t o r , Predictions of t h e fission-associated gamma-ray spectra have not been Therefore, experiments attempted on the basis of the theories of fission. provide the only access t o these spectra. ray spectrum i n time coincidence with fission used for a source the U-235 Experiments t o determine the gamma-* Oak Ridge National Laboratory, operated by Union Carbide Corporation f o r the U. S. Atomic Energy Commission. Throughout this paper, references t o f i s s i o n imply f i s s i o n of U-235 by thermal neutron capture.

Correlation measurements of fission-fragment properties

“…as obtained from previous measurements [28]. Although the experimental spectrum is not corrected for efficiency yet and only a part of the taken data is analyzed so far, the good agreement is promising.…”

Photon energy spectra in the vicinity of nuclear reactors.

“…They showed that the spectrum was represented in analytical forms. 19 The spectrum calculated with their analytical formula is also given in a dashed curve after being normalized to 1 count per second at 7 MeV in Fig. 2-a).…”

A Method for the Numerical Integration of the Photon Transport Equation in Slab Geometry

“…are expressed in the form of separated variables. That is, (9) As mentioned previously the coefficients a,. become fixed when 2Q is chosen, and the K,(X 1 ) 's are easily evaluated as indicated by Eq.…”