LNT and "METHOD"?

[FRAMEP@ORAU.GOV]

Dr. Spahn is to be thanked for his reasoned and unemotional contribution
on the subject of the LNT model.

> A colleague asked about analyzing soil for Ra-226 using "in-growth
gamma
> method". Is there a formal or regulatory "Method" (e.g., EPA) or is the
> reference simply to counting Pb-214 and Bi-214 markers?

While I am unfamiliar with the citations recommended by my good friend
Ed Tupin, let me offer the following thoughts on quantifying radium in soil
by gamma spec

Calibrate with a soil standard of similar density if possible.  Fill the
container completely  -  if radon builds up in the air space above the soil,
the decay products might plate out on the walls of the container -
something that would introduce uncertainty in the estimated counting
efficiency.

Quantify primarily with the Pb-214.  Bi-214 has a higher energy gamma at
609 keV (less self absorption)  but it is subject to coincidence losses. 
The effect of this could be reduced by counting further away from the
detector but I assume the radium levels are fairly low.

Also quantify  the Bi-214 for fun - its activity will appear slightly less than
that of the Pb-214 because of the coincidence losses. Also for fun
quantify the  Ra-226 with the 186 keV line. The activity might be higher
than that determined for the lead and bismuth because of contributions
from U-235's 186 (or so) keV gamma. Also, use an intensity of 3.6% for
the Ra-226 gamma rather than the 3.3% intensity that your library might
attribute to it.

Make sure the container is well sealed so that there are no radon losses.
If time permits, give the sample (in the container) a couple of weeks for
the radon to come into equilibrium.

Needless to say, most of this is overkill.

Best wishes

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov