Dose estimates for the heavy concrete ratchet wall configuration

During the 1987 meeting of the APS User's Subcommittee on Conventional Facilities, we were urged to study changes in shield-wall geometry for the storage ring so as to provide an increased portion of the photon beam outside that shield. The shield-wall position, with respect to the source point, is a geometric function of the thickness of the wall, the clearance between the photon beam inside the wall (front-end area), and the corresponding clearance outside the wall. The relationship of any of these three dimensions and the resulting movement of the ratchet portion of the wall (and thus the portion of the beam line outside the shield) is about one-to-eleven, so that for each inch given up in clearance or wall thickness, eleven inches of beam-line length is exposed. Unfortunately, the two clearances were already considered minimal, and the shield-wall thickness determines the radiation dose received on the operating floor and is not really a open-quote free parameterclose quotes. The first change made in geometry was to consider the use of heavy concrete for the wall construction. (The inner wall and roof are still considered to be normal concrete.) A thickness of 0.56 m was chosen, since that provided the same shield quality as the former 0.8-m normal concrete wall. The ratchet thickness itself was left at 0.8 m for several reasons: the wall encloses a lead/concrete plug of 0.8 m total length; there is only a one-to-one relationship between this dimension and the beam-line length exposed; and the 0.8-m length will prove to be important in consideration of the forward-angle bremsstrahlung radiation