RE: A hunting we will go!

[Eric Denison <denison.8@osu.edu>]

Christopher H. Clement wrote:

>With respect to finding your thorium hot spot, you might be able to
>estimate it's depth by looking at the relative observed "strength" of
>two or more peaks in your spectra.  Our office is studying similar
>techniques to be applied to radium sources.  Let me know if you would
>like more information.

You might also be able to estimate depth by taking measurements both at the
surface and at some distance above the surface (especially if you're
looking at the 2.6 MeV gammas from the Tl-208).  Apply the standard
shielding equations to the soil-only readings and the soil-plus-air (or
soil plus whatever other attenuator you choose) and you should get a fairly
simple two-equation/two-unknown system.  Solve for the mass thickness of
the soil, divide by the density, and you have the distance below the
surface.

Alternately, examine the pattern of the drop-off of the readings around the
"hottest" spot.  Taking the source as a point mass, a straight line of
readings on the surface will effectively describe a chord of a circle
centered on the mass.  A little geometry should give the location of the
center.

Only one hitch to both of these methods, though.  I'm having trouble
determining whether you will locate the top of the mass or the center,
though.  If it's not too spread out, it shouldn't matter much.

Good luck!

Eric

J. Eric Denison
Program Assistant to the Director
Neurobiotechnology Center
The Ohio State University
206 Rightmire Hall
1060 Carmack Road
Columbus, Ohio  43210
ph: 614-292-5682
fax:614-292-5379
e-mail: denison.8@osu.edu