Re: Dosimetry

[denison.8@osu.edu]

In the discussion of cost savings from quarterly dosimetry versus monthly,
the important aspect of processing time seems to have been forgotten.  Jim
Abraham's example also makes the mistaken assumption that the vendor has to
give out fresh new badges every month and throw the old ones out.  This may
be true for film, but TLD's will be re-used.

Assume the following (for convenience):
* 100% of your 1000 TLD's are returned on time every month (improbable);
* processing takes 1 month (this includes sending them back and
  having them read, refurbished, sent back to your facility);
* every TLD can be re-used (no chipping, breaking or aging effects).

If you're on a monthly program, a quick calculation shows that the vendor
will have to essentially devote 2000 TLD's to the exclusive use of your
facility -- one set in use and one set in "processing" at any given time.
Remember that this assumes 100% timely return.  If some of your people lose
their badges or turn them in late, the number goes up.

If you go to quarterly, it's fairly easy to see that 4 groups of 1000
badges can support 3 facilities with 1000 employees each if the start dates
for the facilities are offset correctly (one starts in January, April, July
and October; another starts in Feb, May, Aug and Nov; the third starts in
Mar, Jun, Sep and Dec).  This puts three sets in use and one set in
"processing" at any given time.  Again, we're assuming 100% return and 100%
reusability.  4000 quarterly badges for 3 facilities is only a 33% decrease
from the 6000 needed to support monthly exchange.

The cost of "processing" the TLD's your facility uses should go down by 2/3
because the vendor is only doing your TLD's four times a year instead of
twelve, but the number of TLD's they have to buy, maintain and keep in
inventory only goes down by 1/3 at the most.

Also consider the fact that quarterly TLD's have to be more stable and
better able to "hold a dose" over a long period of time than monthly ones.
This probably means that the TLD and supporting materials are more
expensive than stuff that only has to last a month.

I'm not sure where Sandy came up with the "utilization potential" thing,
but since the total cost to the vendor is a combination of buying,
maintaining and processing the TLD's, you can't expect a 67% drop in the
cost just because your exchange frequency dropped that much.


J. Eric Denison
Nuclear Engineering Program
The Ohio State University
2030 Robinson Laboratory
206 West 18th Avenue
Columbus OH 43210
(614) 292-3681 or -1074
denison.8@osu.edu


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