Experimental study on additional shields for leakage gamma rays from a duct

For the purpose of providing experimental data for the assessment of shielding calculations, gamma-ray dose rate distributions are measured around a rectangular shield in a concrete cavity installed at the outlet of a radiation beam hole of the research reactor JRR-4. The shield consists of concrete, iron, and lead slabs. Measurements are performed for twenty configurations which are selected from the combination of the shield slab sequence and the shield location in the cavity. The following conclusions are obtained through the analysis of experimental data. (1) Gamma rays scattered at the duct outlet play important role in the determination of dose rates around the shield. (2) For the high energy gamma rays above 4 MeV, a better shielding effect can be obtained by setting heavier materials to the source side. The ray-effect found in the calculation by the discrete ordinates transport code PALLAS is solved by calculating uncollided fluxes analytically. Calculations by the Monte Carlo code MORSE agree fairly well with experimental results except in the side of the shield where large inconsistencies are found. (author)