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Re: Radiation Effects and Computors
At 21:26 03/07/98 -0600, you wrote:
>I do not know of any permanent effects on semiconductor junctions or
>magnetic material caused by the sort of dose rates likely to be experienced
>during the tests. My assumptions are based on the following:
>
>1. Dose rate from 65 Ci Ir 192 about 32 RAD /h. Dose rate at 12 m about
>220 mRAD/h.
It's not dose rate, it's total dose that is the concern. The space
environment
is a lot less than 30R/h and some satelites fail in only a few years. It also
depends greatly upon the part, the package it's in, the angle WRT the
radiation
and what the part technology is. I can go on for pages.
>2 The beam should be limited with a collimator. The above dose rate should
>only be in the useful direction This dose rate would be attenuated by the
>floor (the part under examination).
A good idea period. ALARA put to good use.
>I would imagine that dose rate 2 or 3 orders of magnitude higher would may
>be necessary to see an obvious change in a germanium reversed biased
>junction.
Depends on the effect you're looking for. If you want to degrade the voltage
needed for the junction to work, any dose rate will do. For single event
disasters (see the optocouplers in Hubble), a single, high energy proton is
all that is necessary. Fortunately very rare on earth.
>In summary if computers within 3 m of the exposed source were turned off (
>which may be an unnecessary precaution) I would be surprised if any effects
>whatsoever would be detected.
Actually, a very good idea to turn them off. The effects for parts not under
bias (ie. not turned on) is on the order of a thousand times less than for
parts that are turned on. Why worry if turning the thing off will take away
virtually all problems?
Scott Kniffin
mailto:Scott.D.Kniffin.1@gsfc.nasa.gov
RSO, Unisys Corp. @ Lanham, MD
CHO, Radiation Effects Facility, GSFC, NASA, Greenbelt, MD
The opinions expressed here are my own. They do not necessarily represent
the views of Unisys Corporation or NASA. This information has not been
reviewed by my employer or supervisor.
>
>Best Regards
>M.Malaxos
>Radiation Safety Services
>69-71 Robinson Avenue Belmont
>Western Australia. 6104
>Fax 61 89 475 0165
>P 61 89 475 0099 a/h 089 255 1214
>email rss@arach.net.au
>
>