SU‐E‐T‐243: Design of a Novel Testing Port for Radiation Protection and Shielding Measurements

Abstract

Purpose:The majority of radiation shielding research utilizes Monte Carlo simulation because of the difficulty in eliminating secondary radiations from measurements. We have designed a test port into a primary barrier of our newest vault to allow for shielding measurements while ensuring adequate protection to the public and staff during normal machine operation. This port allows for measurement of attenuation values of shielding materials, differential dose albedos, and radiation scatter fractions.Methods:The vault design utilized the maze as part of a compound primary barrier. The test port is contained within the maze and is centered along isocenter. The inner 30 cm has a 20×20 cm2 opening, while the remaining length has a 30×30 cm2 opening. The block that contains the port has a density of 200 pcf to minimize internal scatter. The 30×30 cm2 opening is occupied by removable 215 pcf concrete blocks. The innermost and outermost blocks activate an interlock wired into the beam‐enable loop. This disallows beam‐on in treatment mode if the interlock isn't closed. The interlock can be overridden in service mode, or by‐passed via an override switch in case of circuit failure.Results:The test port was installed in August. The beam is disabled when the interlock is tripped. Measurements taken when the primary beam is not incident on the port are indistinguishable from background. Ambient dose levels surrounding the vault with the designed shielding blocks in place are all within allowable limits for occupational workers.Conclusions:We have designed and installed a unique testing port for radiation protection and shielding measurements. This port is appropriately interlocked and designed to mitigate any risks of incidental exposure to staff or members of the public. The test port design allows measurements with “good geometry” and efficient removal of contaminating sources of radiation present in many shielding measurements.Daniel Harrell and Jim Noller are employees of Shielding Construction Solutions, Inc, the shielding construction company that built the vault discussed in this abstract. Manjit Chopra is an employee of Universal Minerals International, Inc, the company that provided the aggregates for the high density concretes used in the vault construction.