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Susceptibility of Microcomputers to Malfunction Induced by Neutron Radiation Exposure in Proton Therapy Environments

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J Herrington

J Herrington1*, Y Chen1 , S Ahmad1 , C Ferreira2 (1) University of Oklahoma HSC, Oklahoma City, OK (2) University of Minnesota, Minneapolis, MN


SU-I-GPD-T-203 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To measure acute and cumulative effects of neutron exposure of Intel-based microcomputers in a Mevion S250 double scatter proton treatment room accounting for CPU process sizes.

Methods: Computer configurations used Intel Core2 Duo E8000 and E6000 CPUs with process sizes of 45nm and 65nm respectively, 160GB HDD (areal density of 37Gb/cm2), and 4x1GB, non-ECC, DDR2 memory. Computers were subjected to 24h stress testing prior to exposure to ensure stability. Proton beams were delivered to solid water blocks at 164.4cm SSD and CPUs were placed at 219.4cm SSD. Neutron effective dose at CPU location was measured with a Wendi-2 neutron detector. Total dose of 80Gy was delivered in three fractions (20, 20, and 40Gy). Acute effects of radiation on computer’s operation during irradiation were determined by: Prime95 stress tests, system errors reported by operating system (OS), RAM and HDD testing using in-house software. After each fraction, computer stability was stress tested for 24 hours. RAM and HDD integrities were tested.

Results: Computers experienced fatal system errors during exposure resulting in OS crash with CPU reporting errors to the OS. In 45nm and 65nm systems, threshold doses to produce fatal errors ranged from 0.07mSv 0.67mSv and 0.13mSv-1.17mSv, respectively. RAM experienced 1error/2.74mSv while HDD presented 1error/10.94mSv. No permanent hardware defects in RAM or HDDs of any system were detected. Post-exposure stress testing revealed cumulative effect in only one 65nm system tested: 1error/11.750h (0.91mSv), 1error/7.625h (3.65mSv) and 1error/1.625h (7.30mSv).

Conclusion: Acute neutron exposure of microcomputers renders CPUs unstable and prone to unrecoverable errors and crashes. Smaller process sizes were more susceptible. RAM and HDDs were susceptible to soft errors, which can lead to instability, but no permanent effects were observed. Cumulative effect on CPUs at doses tested appeared minimal though permanent instability was observed in one system.

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