SU‐E‐T‐178: Can a Portal Monitor Be Used for Screening of Population from Radiological Terrorism Events?
Purpose: The purpose of this study is to obtain physics characteristics of a portal monitor and to study the feasibility of its use in a radiological emergency, more specifically from radiological dispersal devices (RDDs).Methods: Two Cs‐137 sources with activity of 0.953 μCi and 1.50 mCi were used. Two physics characteristics were investigated: (a) angular dependence outside of the portal monitor, and (b) distance dependence from sources outside of the portal monitor. Queue theory was applied to the physics characterization measurements in order to evaluate the utility of the portal monitor in a radiological emergency. Results: The portal monitor detected the low activity source outside of the portal monitor at various angles at distances between 0.2 m and 0.3 m. It also detected the low activity when it was 0.25 m from the center of the portal monitor. This measurement was repeated with the 1.50 mCi Cs‐137 source. We found that the 1.50 mCi Cs‐137 source could be detected 3.0 m from the center of the portal monitor and the exposure rate was measured to be 30 μR/hr at the center of the portal monitor. Assuming collective contamination with 100 mCi of Cs‐137 in the RDD scenario, the portal monitor would have to be placed approximately 40 m away from people waiting to be scanned. Additionally, portal monitors should be 10 m from each other if multiple are used Conclusions: The portal monitor is designed for the detection of small amount of contamination (∼1 μCi) for screening employees in commercial nuclear facilities. The portal monitor could be improved by adding shielding and collimation around the detectors and by decreasing the sensitivity for RDD applications. Without these improvements, the portal monitor cannot be deployed in a radiological emergency in urban areas because of the space needed to avoid false positive readings. © 2011, American Association of Physicists in Medicine. All rights reserved.
Fredrickson, M; Yoshizumi, T
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