Re: S-35 Radioactive Contamination

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

Ms. Jacob,

>Yesterday, a student's thumb was contaminated with S-35 methionine. I
>estimated 54 nCi in  a 1/2' X1/2" square area of the thumb.
>Today the activity is down to 18 nCi. Is this because of the desquamation
>of the skin or is there some absorption also?

I've looked shallowly into literature on horny layer skin sloughing.  That,
and an experiment performed on my own skin using a permanent ink marker,
leads me to believe the horny (dead) skin layer replaces itself, at a linear
rate, every 10 (or so) days.

It wouldn't surprise me if some absorption was going on, too ...

>What would be your advice on taking a  urine sample? grab sample? 24 hour
>sample?

If all 54 nCi went into the student's system, using the lower of two ALI's
published in NRC regs (6000 microCi), that would deliver a dose equivalent
to 4.5E-02 mrem.  Much less than 10% of any dose limit.  So if you are
*sure* the only personnel contamination that occurred was that thumb spot,
you needn't mess with urine.

If you did take a urine sample, and got data, how would you evaluate it?
NUREG/CR-4884 deals with "acute" intakes, not intakes that trickle into
one's system over days.

>Does anyone have a program that would calculate the dose to the skin at
>that area?

Probably.  But if you have to do it by hand:

1 - Instantaneous dose rate can be determined from activity density (there
are publications with tables).

2 - Calculate the "effective decay constant" of the skin spot.  (54 to 18
nCi in how many hours?   A little algebra will give you "lambda" in inverse
hours.)

3 - Divide the initial dose rate by the "lambda" observed.  This is
equivalent to integrating the exponential decay to infinite time.

Albert Lee Vest                   Radiation Safety
Health Physicist   Environmental Health and Safety
(614)292-0122            The Ohio State University
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