Re: Regulations from scratch

[Ccja@aol.com]

In the case of badges for which the LLD is 10 mrem (typically this is for
photons, neutrons are more likely to be LLD'd at 20 mrem, betas might be 30),
an exposure report of minimal ("M") signifies an exposure of less than 10
mrem, i.e., 9 (or 9.9, if you like) and below. The minimum detectable per
unit time is a simple, multiplicative function of the number of badges worn.
If 12 badges were worn over a period of a year, and all of them reported
minimally, the best one could say about that person's exposure, considering
only the measurements, would be that it was less than 120 mrem. In fact, this
would be true up to the point at which all of the badges reported exposures
of at least 10 mrem; that is, if 11 badges report 10 mrem, and one reports
minimally, still the best one can say, considering only the measurements, is
that the exposure was (110 + M) < 120 mrem.

Of course, one could rationalize this by observing that if the "true"
exposure rate was, say, 60-120 mrem/y, then one would have seen spikes, such
that occasional badges would have reported at or above 10 mrem, therefore
that the true exposure rate was probably below that range. (As an aside, note
that if the reported exposure of an individual badge is <10xLLD, then the
error in the measurement is equal to the LLD, by definition, because that's
the smallest reportable increment of exposure, so that at the LLD, the error
is 100%, here 10+/-10mrem.) But that's no longer a pure measurement.

I recommend the use of TLD's, rather than film, when attempting to monitor
people at these levels of "exposure". The use of 4 TLD badges, exchanged on a
quarterly basis, would lower the annual LLD to 40 mrem. One can also save a
good deal of paperwork and even some hard cash, since one can usually save
10% or more, on the cost of the badges, in substituting one quarterly badge
for three monthlies.

The question of when to monitor a population, or subgroup thereof, is always
fraught with sociopolitical pitfalls. If you're asking for a hard target, I
suggest 100 mrem/year. I mean that if one knows, and can demonstrate, by
calculation, surveys, test monitoring, etc., that the individuals in a given
group are unlikely to exceed that level, then the additional documentation
provided by continuous monitoring is not justifiable, or needed.

Chris Alston