~ Pergamon 0306-4549(94)00048-4 Ann. Nucl. Energy Vol. 22, No. 5, pp. 297-302, 1995 Copyright © 1995Elsevier Science Ltd Printed in Great Britain.All rights reserved 0306-4549195$9.50+0.00 ANGULAR PROPERTIES OF THE SCATTERED PHOTONS FOR COMBINED 1.43 AND 2.75 MeV SOURCE PHOTONS PENETRATING SINGLE AND DOUBLE-LAYER SHIELDS G. C. BAKOS Nuclear Engineering Laboratory, Department of Electrical Engineering, Democritos University of Thrace, 67 100 Xanthi, Greece (Received 8 June 1994) Alrstract--In this paper, experimentally determined angular flux spectra for combined source energies of 1.43 and 2.75 MeV, penetrating single and double layer shields, are examined. Changes in the total scattered photon energy spectrum, as a function of polar angle and shield thickness, are also discussed. For any given polar angle, the scattered photon properties decrease exponentially with increasing shield thickness. Recently, similar conclusions were reported for single source photon energy (Kappos and Bishop, 1987). INTRODUCTION Angular benchmark data and properties of the energy of the scattered photons for 6.13 MeV source photons have been presented (Bishop and Banai, 1985; Bishop, 1985). Similar data for single source energy of 1.43 MeV using ammonium metavanadate solution and of 2.75 MeV using activated sodium carbonate solution has been reported by Kappos et al. (1986). Experiments have been carried out to determine angular photon distributions for ),-rays, produced by disc source geometry (Na-24), penetrating single and double layer slabs. The angular distributions were obtained by unfolding the output pulse heights from a highly collimated scintillation detector using the code RADAK (Grimstone, 1976). Angular flux spectra were examined for combined source energy of 1.43 and 2.75 MeV for A1, Pb, 12"A1+ Fe, 12"A1+ Pb, 4"Pb + A1 and 4"Pb + Fe layer shields. CALCULATION OF SCATTERED PHOTON ENERGY One property of interest is the energy of the scattered photons Es(MeV). Values of E~ at any polar angle 0 can be derived using the expression: n E~(0) = ~ E~(Ixx,E,,0)A E~ (1) i=l where n = number of bins in the unfolded solution relating to the scattered photons below source energy O~(lax,E~,0)=double differential angular flux spectra (photons/cm2 s sr MeV) rtx = shield thickness in mean free paths (m.f.p.) E~= nominal energy group AEi = energy group width The experimental data is given in a 21-group energy distribution and two peaks of photon flux were observed in the groups i= 13 and i=21 for the corresponding energies E~ = 1.43 MeV and E2=2.75 MeV. For the combined source energies (1.43 and 2.75 MeV), equation (1) is modified as follows: 297