[ RadSafe ] Low temps and CF-252 sources

Baumbaugh, Joel SPAWAR joel.baumbaugh at navy.mil
Sat Feb 16 13:20:56 CST 2008

Below (in larger font)  is a similar question that I asked/posed on RADSAFE "quite" a few years ago...(1995).  What type of sources are YOUR researchers using?  The sources in my question below were ICN-375's and they were/are pretty rugged sources. The sources are still in use to this day and (knock on wood) have had no leakage problems (they just don't make them like they used to.. LOL).  
When I last asked my question to RADSAFE, no one had had a similar experience with extreme cold and sources - in my case using dry-ice (-109.3 F) to initially cool the sources, and then into liquid nitrogen (-321 F)  and then into liquid helium (-452 F).  I think that the greatest potential for damage is the thermal shock - especially w/the welds - which we tried to minimize w/the cooling routine above.
Here was my initial question:
   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 as to 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.


     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..

So, Brian, in my case, so far so good.... I hope that your researchers are VERY careful w/the sources at these temperatures - don't knock/hit them against anything as the metal DOES become quite brittle...  I always swiped them before after use (when they were warmed back up to room temperature of course)...

Hope this has helped...

Joel Baumbaugh - SSC-SD...


From: radsafe-bounces at radlab.nl on behalf of Brian Rees
Sent: Fri 2/15/2008 2:34 PM
To: radsafe at radlab.nl
Subject: [ RadSafe ] Low temps and CF-252 sources

We have a researcher that in interested in taking a Cf-252 source to 77k
(-196C) - Liquid N2 as part of an experiment.  I assume the encapsulation
is not tested to that low a temp, and I would have concerns about brittle
fracture and/or thermal expansion/contraction induced cracking of the
encapsulation - not something I would want to deal with!   Other than
speculation (which we are also quite capable of) does anyone have any
information or experience in this realm?

Thanks in advance,
Brian Rees


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