A maze design is discussed for a Therac 20 linear accelerator (manufactured by Atomic Energy of Canada, Ltd.) which reduces the flux of neutrons at the door to permissible levels in controlled areas. The L-shaped design allows for a relatively light door at the end of the maze, consisting of 5.08-cm (2-in.) borated polyethylene and 2-mm lead. A comparison is made between the neutron dose equivalent (DE) calculated by various methods and the DE measured with a variety of portable neutron survey meters. In addition, the neutron energy spectrum outside the maze at 1 m from the door, measured with a polyethylene multisphere LiI system, is reported.
The specialized radiological safety considerations of ATLAS were discussed in 1982 (1). This paper will present the details of the hardware, the administrative controls, and the radiation monitoring that will be in effect when beam is produced in April 1985. The experimental hall utilizing the maximum energy beam (~ 27 MeV per nucleon) from the completed ATLAS has been partitioned with shielding blocks into its final configuration. Because scientists want access to some of the partitioned-off areas while beam is present in other areas, an interlock and logic system allowing such occupancy has been designed. The rationale and hardware of the system will be discussed. Since one of the potential radiation hazards is high-energy forward-directed neutrons from any location where the beam impinges (such as collimators, bending and focussing systems, experimental targets, and beam stops), radiation surveys and hazard assessments are necessary for the administrative controls that allow occupancy of various areas. Because of the various uses of ATLAS, neutrons (the dominant beam hazard) will be non-existant in some experiments, will be of energies 10 MeV for a few experiments. These conditions may exist at specific locations during beam preparation but may change rapidly when beam is finally 1 delivered to an experimental area. Monitoring and assessing such time varying and geographically changing hazards will be a challenge since little data will be available on source terms until various beams are produced of sufficient intensity and energy to make measurements. How the operating division for ATLAS and the Argonne safety division are addressing this aspect through administrative controls will also be discussed.
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