Re: Fume Hood Decontamination

[EFJ@asbhr.byu.edu]

> My suggestion is to just wipe test the whole area and divide the DPM by
> the area wiped. Anything over 200 DPM/100 cm2 would have to be cleaned.
> With the small number of users, you could also just wipe down all the
> hoods before testing them just to be sure.

Your survey protocol should be dictated by the type of nuclide
contamination expected.  If there is no way to determine the nature
of nuclides used in the hood I would plan to survey for gamma, beta,
and alpha emitters.  You will also probably want to determine both
fixed and removable contamination.

For fixed contamination I would use a thin window beta probe for any
beta with average energy over 49 kev.  I'd calibrate with a 14C
source at the low end (if you have a calibrated source available). For
alpha emitters there are a number of good probes on the market.  For
gamma emitters I would use a solid scintillation probe (NaI or
similar). If you are looking for fixed 3H contamination there are not
a lot of good tools available.  I have an open window portable tritium
detector but I'm not extremely fond of the  ___ thing.
Swipes will be very useful in determining removable surface
contamination but they are not too useful for fixed contamination.
If your swipe counter can be set up to differentiate alpha emissions
from betas and photons life can be somewhat easier.  Usually removable
alpha surface contamination should be less than 20 dpm/100cm2 whereas
beta and gamma emitters would be somewhat less restrictive.

good luck

______________________________________________________________________

Name: Edwin Jackson
EFJ@ASBHR
Environmental Coordinator
Brigham Young University