Re: Request for info - gamma contamination instrumentation: 5k dpm

["Scott O. Schwahn" <schwahn@CEBAF.GOV>]

There was a paper presented at the 14th International Conference on the
Applications of Accelerators in Research and Industry on that very subject.
It presented a methodology for detection and establishing contamination
limits for these "loophole" radionuclides; by loophole I mean that they are
implied but don't fall directly under the beta-gamma category, being that
they are electron-capture gamma emitters.

>...we are
>getting increasingly higher fractions of electron capture isotopes in our
>isotopic mix.
>
>...
>
>Please answer the following questions to help us in our quest for a
>practical, field usable gamma sensitive contamination detection instrument.
>
>1. Do any of your source terms include a high fraction (>50%) of electron
>capture isotopes?

Yes, as an electron accelerator, we have mostly positron or electron-capture
radionuclides.

>
>2. If yes, what contamination monitoring instrumentation do you use for
>unconditional release of materials?

Oooooh.  Unconditional release.  Not a pretty subject in the DOE (U.S.
Department of Energy) world.  Each facility has to come up with its own
release methodology that has to be approved by EH (Environment & Health, I
think) division of the DOE.

>
>3. Do you use any handheld gamma sensitive contamination detection
>instrumentation for unconditional release surveys and/or in-field
>contamination surveys?

We have applied to the DOE for a count-rate based contamination control
standard for contamination surveys...  in short, we have presented a case
that based on the ALIs (Allowable Limits on Intake) for the radionuclides we
find here, that a 100 cpm/dm^2 count rate for any and all of our usual
radionuclides is adequate, using Co-60 as a basis for comparison.

>
>4. If yes, what instruments do you use and how sucessful have you been with
>them?

Standard "frisker" type GM detectors.  Again, because we are proposing a
count-rate based contamination control standard.  Success?  Can't measure
success until we are approved to use it.  Actually, for now, we are taking
swipes and running them back to the reverse-electrode intrinsic germanium
detector for analysis based on the (often low-E, low branching) photons.
Not very practical for you, but it is workable with us, as we can easily
narrow down where contamination will be based on localized beam losses.

Scott O. Schwahn, CHP
Jefferson Lab, M.S. 12A1
12000 Jefferson Avenue
Newport News, VA 23606
(757)269-7551 (w)
(757)269-7363 (fax)
schwahn@jlab.org