Is Bentonite Clay supposed to be "radioactive" -Reply

[FRAMEP@ORAU.GOV]

>Have any of you encountered noticeable levels of radioactivity
>(>2xbkg) associated with bentonite clay?  I did not find bentonite
>clays identified as a mineral source of unusual radioactivity in the
>collection of NRCP handbooks on my bookshelf.

Nancy?

Yep. The analyses on bentonite that we have done show 3 to 6 pC/g for
both the uranium and thorium series. The K-40 levels were a little
low i.e. 4-5 pCi/g. I can only say this for the bentonite that we
have looked at. It probably varies a little with the source.

Since the stuff comes in a nice granular form, is well mixed and
cheap, we once used it to make volume standards of various dimensions
for gamma spectroscopy.

Another commonly encountered clay that shows a similar activity is
koalin, the biggest export product out of Georgia. They used to use
it in Kaopectate, in fact that's all Kaopectate used to be- clay.
(they changed the formula some 5 years ago). We did the calculations
for the state of Georgia and found that you had to ingest about one
ton of Kaopectate per year to exceed the ALI. Obviously anyone
ingesting one ton of Kaopectate per year has more important things to
worry about than exceeding the ALI.  Kaolins biggest use is in the
production of glossy paper for magazines: the pictures look better on
the smooth glossy surface. I actually ran across a Playboy magazine
hidden away here at work, cut it up on a bandsaw, put it in a
marinelli and did the analysis. Based on the activity, I estimated
that the exposure rate above background from reading the thing was
1.5 nR/hr above background. The annual population exposure from
Playboy is about 0.5 man-rem if I remember it right. Jack Beck, whom
some might know, was visiting our place at the time. When I showed
him the analysis and spectrum, his mouth fell open and he asked
"Whats the critical organ?"

Paul Frame
Professional Training Programs
Oak Ridge Institute for Science and Education
framep@orau.gov