How cold can I go...

[baumbaug@nosc.mil (Joel T. Baumbaugh)]

     A  research  lab, where I work has to, upon occasion,  check
equipment  operation  at very cold temperatures i.e.  77  degrees
kelvin  (-195  C) or colder (4.2 K).  I'm sorry that I  can't  go
into specific details of why (and where).

     My  researchers  are currently using a 6 year old ICN  model
375  sealed  source  (Co-60) which for all of its life  has  been
exposed  to  these  extreme  temperatures.   Understandably,  the
manufacture  (which  no  longer manufactures these  sources)  was
surprised  at  the temperature at which their sources were  being
subjected  to  and is somewhat reluctant to guarantee that  their
sources are going to hold up to this treatment in the future.

     My  immediate  thoughts were along the path of "If it  ain't
broke,  then don't fix it", but, of course, it took an inspection
by  a  group  of bored inspectors to insist on  documentation  to
"guarantee" that it is a safe process.


     Questions:

     1.    Has anyone else had a similar experience?  Please tell
me about it.

     2.    Does  anyone have any concrete data on  whether  these
double-walled   stainless  steel  capsules  can  withstand  these
thermal  stresses  indefinitely - or until the source becomes  so
old as to be impractical...Inquiring minds want to know..


     Thank you all a head of time,

     Joel Baumbaugh  ( baumbaug@nosc.mil )