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Re: Neutrons and Computers
>Date: Fri, 12 Nov 1999 16:07:48 -0600
>Reply-To: "Frank R. Borger_(FRB)" <frb@GAMMEX.COM>
>Sender: Medical Physics Mailing List <medphys@cwis-20.wayne.edu>
>From: "Frank R. Borger_(FRB)" <frb@GAMMEX.COM>
>Subject: Re: Neutrons and Computers
>X-To: peter.vitali@YALE.EDU
>To: MEDPHYS@cwis-20.wayne.edu
>
>The problem with radiation damage to electronics has been around a long time,
>but is surfacing more now with higher density (smaller size) dies.
>
>Long term effects are shortened life for electronics, (re some multiple
chamber
>constancy devices that have circuit boards under the detectors.)
>
>Short term effects are units like the Varian Thebes that can be really
smoked in
>a relatively short time if the electronics is exposed.
>
>I once built a linac add-on that incorporated a small single-board micro.
It was
>mounted at a location that it would occasionally be in the beam, (certain
posterior
>oblique beams only.) The unit would occasionally stop, but would be fine
after
>applying the "big red switch"
>
>Sounds like the computer's bios are getting blasted by the neutrons.
>(Remember, the computer uses similar ram for storing setup data, but keeps
>it active with a battery. It's just as subceptible as main memory to
heutron hits.)
>
>A quick fix might be one of the many programs that can save and restore the
>setup parameters from a floppy disk. I'd question, however, the wisdom of
>having a computer system that had to be "fixed" once a week or so.
>
>Frank R. Borger - Senior Support Engineer, Gammex RMI
>fborger@gammex.com phn: 608-828-7289 fax: 608-828-7500
>
>"The few ... The Proud ... The Maroons
>University of Chicago football team motto.
>
>>>> "Peter E. Vitali" <peter.vitali@YALE.EDU> November 12, 1999 11:15 >>>
>To all members of both lists:
>
>Recently we had a problem with a computer in a piece of equipment
>located in one of our treatment rooms. The computer was a new one and
>within one week of being in the room it would not boot up correctly.
>This first computer was replaced by a new one and within one week would
>also not boot up correctly. The representative of the equipment (not
>Varian) said that the problems was caused by neutrons in the room. He
>said that the only places where they were having a problem was when the
>equipment was in a treatment room where the photon energy was 10 MV or
>above. The higher the energy the more breakdowns. We later spoke to a
>representative of another company who said that they had to remove their
>computers from inside of treatment rooms because of this problem. This
>representative also stated that the problem was noticed in those
>computers using the higher internal speeds and that they had not seen
>the problem with computers using the 486 CPU due to the slower speeds of
>these computers. That the cause was that the manufacture of the memory
>chips in the computers, in order to obtain more speed, decreased the
>thickness of the mask in the chips from 5 microns to 3 microns, which
>then made them more susceptible to thermal neutrons. The neutrons would
>then change the memory state in the chips.
>
>Question: Does anyone have more information on the above and is my
>information correct? How many have seen this problem? Also since
>shielding is not prefect, has anyone seen this problem with equipment
>outside of the treatment room? Is this phenomena only effecting the
>boot up memory or is it also affecting other memory in the computers?
>
>The computers that we had the problems with were in a treatment room
>with a 6/18 MV linac.
>
>Peter E. Vitali, CBET
>Therapeutic Radiological Engineer
>Department of Radiation Physics
>Yale-New Haven Hospital
>15 York Street
>New Haven, CT. 06504 U.S.A.
>Tel: 203 688-2948
>Fax: 203 688-3663
>E-Mail: peter.vitali@yale.edu
>
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>Attachment Converted: "d:\eudora\attach\Maroons.sig"
Frank R. Borger - Senior Support Engineer, Gammex RMI
fborger@gammex.com phn: 608-828-7289 fax: 608-828-7500
"The few ... The Proud ... The Maroons
University of Chicago football team motto.