Radon emanation from surface contamination -Reply

[ABELQUIE@ORAU.GOV]

Christopher wrote:

I'm interested in interpreting measurements taken with a pancake Geiger
on radium contaminated surfaces.  This radium is old, so all of the
progeny have pretty much grown in, except maybe for the effects of
radon
emanation.  Does anyone have any references out there which might
give
me an idea of how much radon emanation may be taking place from this
type of contamination?

-----------------------------------------

Christopher-

This is an interesting problem.  Even if one were to assume that complete
equilibrium existed throughout the Ra-226 chain, the interpretation of the
GM pancake response must carefully consider its efficiency to a number
of alphas and betas (i.e. varying energies and radiation yields).  Thus, it
is possible to obtain an overall efficiency of the GM to radium and
progeny for the situation of complete equilibrium. We estimated an
efficiency for the entire chain (9 radionuclides) of 127% for radium on
stainless steel (about 14% per radionuclide in chain).  The main
contributors to detector response were Pb-214, Bi-214, and Bi-210
betas.

Now, considering that complete equilibrium may not (probably not?) exist
on these surfaces due to radon emanation, the fraction of progeny
present must be assumed or measured.  One technique may be to collect
an in situ gamma spectrum on this material to show the relative ratios of
progeny present.  Or assumptions using the indoor equilibrium factors of
radon and progeny can be used as an approximation (I believe this is in
an NCRP). Once the fractional abundance of progeny has been
estimated, the GM response can be modified to account for the mix of
radionuclides present.  

I'm sorry I don't have an answer to your specific question. I too would
like to hear from anyone who has estimates on the equilibrium status of
progeny on radium-contaminated material.

Regards,
Eric Abelquist
abelquie@orau.gov