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Cs-137 as a gamma source

  1. Jun 18, 2013 #1
    So I have a bit of a story here. First of all, I work in my university's radiation safety department, where, among other things, I calibrate Geiger Counters. I also passed Modern Physics (Physics III), so I got some education on radioactive decay.

    I have an old Counter from 1962, a Victoreen CDV-715, the one from the Civilian Defense boxes, model 1A. I replaced the battery, and it works, but it hasn't been calibrated since 1988. I calibrate meters all the time, but I use Cs-137 sources, in the mCi range, when first installed in 1992. My problem is that this meter requires Gamma sources to calibrated, and Cs-137 only has about 5.6% chance to decay the the meta-stable Ba-137, half-life about 3 minutes. Only in meta-stable Barium will it give off gamma radiation, .992 MeV worth. Does anyone who also deals with this stuff have a thought as to how I might go about using the Cs-137 sources to successfully calibrate this old meter? I can got it working, but wouldn't it be neat to get it FUNCTIONAL? Then when I get my hands on other old meters my office is throwing away, I can fix them as well!

    I don't have the exact activity from the 6 sources I use to calibrate meters right now, but I can get all that info tomorrow. I'm just not at work right now. I can get their activity at any date, even in the future, as predicted by their decay models. I have all the formulas about activity and decay rates and distances and the like, I just need someone's input to put all these pieces together.

    Thanks in advance!

    Mike
     
  2. jcsd
  3. Jun 18, 2013 #2
    Sorry about that

    I meant .662 MeV of Gamma decay energy. Mistype. Also, I know that if the counter only picks up Gamma radiation, it won't be affected by the β- decay from the Cs-137, I just want to walk through all this logically before I stick it up on the rolling rack and start shooting rays at it. Also, I do have the manual for it.
     
    Last edited: Jun 18, 2013
  4. Jun 18, 2013 #3

    mfb

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    Staff: Mentor

    Well, the direct gamma emission is easy - there is an equilibrium of Ba-137, so 5.6% of the beta-decays lead to a direct gamma decay. On the other hand, your high-energetic electrons can produce gamma rays, too, so you probably get some background.

    Wikipedia has different numbers for the decay probabilities.
     
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