Answer to Question #11397 Submitted to "Ask the Experts"
Category: Security Screening
The following question was answered by an expert in the appropriate field:
I am a registered nurse working in a county jail. This facility has just purchased a RadPRO SECURPASS full-body security screening system for scanning incoming inmates. This is not a backscatter machine; they actually perform body-cavity searches with this machine.
I am located in the triage area where people first enter the jail and where they installed this machine. The operator of the machine is also in the same area but sitting behind the emitter and behind a lead shield that comes with the machine. I am sitting within 2.4 meters (m) of the emitter, facing the emitter portion of this machine for 12 hours per day (h d-1), with nothing between me and the emitter but my particle-board desk.
They have not begun using the machine yet, but I really do not feel safe without some type of shielding between me and the machine, especially since it is used for 12-hour shifts on a full-time basis. I have seen pictures from this machine and they look like regular x-ray images—bones and all can be seen. What do you think? Should I be concerned?
I looked at a report on such devices on the National Criminal Justice Reference Service website. The RadPRO SECURPASS device is presented on page 14 of this report. I also looked at the manufacturer's website for this x-ray device. Both references agree that the person being x rayed receives 0.25 microsieverts (µSv) per scan, which takes about seven to eight seconds (s). I also talked to a service specialist for the machine's manufacturer, Virtual Imaging, Inc., and he said the machine meets the American National Standards Institute recommendation to not expose anyone outside a marked-off area to a radiation dose rate above 0.5 µSv h-1, assuming the machine is running full time during that hour.
So if you work 2,000 hours per year (h y-1) just outside the marked-off area and the machine is on continuously while you are working, your radiation dose would be 1,000 µSv y-1, which is the dose limit for any member of the public established by U.S. Nuclear Regulatory Commission. If the machine is not on continuously, say just one hour each day (about 450 scans a day, which seems like a whole lot of criminals), your maximum dose for 300 working days would be 150 µSv. This is about 5% of the 3,000 µSv radiation dose the average person gets from nature every year.
You can get more details on this machine from the Virtual Imaging, Inc., service specialist at 561-893-8500. I asked him if a second lead shield could be ordered and used with the machine, and he said that this is possible. A second lead shield could be installed to keep your exposure as low as is reasonably achievable, which is good, but a second lead shield may not be necessary, depending on how often the machine is used and the cost of the extra shield.
John Hageman, CHP