Investigation of radiation fields outside the Sub-Critical assembly in Dubna

Abstract

The radiation fields outside the planned experimental Sub-critical Assembly in Dubna (SAD) have been studied in order to provide a basis for the design of the concrete shielding that cover the reactor core. The effective doses around the reactor, induced by leakage of neutrons and photons through the shielding, have been determined for a shielding thickness varying from 100 to 200 cm. It was shown that the neutron flux and the effective dose is higher above the shielding than at the side of it, owing to the higher fraction of high-energy spallation neutrons emitted in the direction of the incident beam protons. At the top, the effective dose was found to be -150 microSv s(-1) for a concrete thickness of 100 cm, while -2.5 microSv s(-1) for a concrete thickness of 200 cm. It was also shown that the high-energy neutrons (> 10 MeV), which are created in the proton-induced spallation interactions in the target, contribute for the major part of the effective doses outside the reactor.

Radiation shielding of high-energy neutrons in SAD

“…The lower-energy neutrons, on the other hand, created in the subsequent evaporation stage and emitted nearly isotropically, constitute only a minor shielding concern, due to their comparatively short range in most shielding materials. For this reason, the largest radiation doses will appear in the forward direction of the incident proton beam [11] and the design of the biological shielding in this direction will generally be of largest importance. The objective of the present paper has been to study the radiation fields and the effective dose where they are maximal, i.e.…”