FW: Accuracy

["Clement, Christopher" <clementc@aecl.ca>]

I agree that any kind of personal dosimeter will only give a rough
measure of the actual external dose received, which is why I am not
interested in a particularly PRECISE dosimeter reading.  What is the
purpose of  precision without accuracy?  Even the 10-20% precision I
mention is probably overkill for this application.

My purpose for monitoring such low incremental doses is only to
demonstrate that good practice has been followed.  Many of our jobs last
only one to five days, and the potential doses are quite low.
Therefore, in order to verify/document that good practice has been
followed I must be able to measure low incremental doses.

>You say
>
>"An uncertainty on the order of 10%-20% or so at these low levels is good
>enough for my purposes. "
>
>I always ask on such occasions "What are you going to do with these numbers
>when you've got them?" 
>
>10-20% is more than good enough for any REAL health physics purpose and
>would be amazing for doses so near to background. Only radiotherapists need
>more accuracy (for their patients, not themselves!). We don't even know for
>sure whether doses as low as you mention are good or bad, let alone just how
>good or bad. We still are highly reliant on difficult interpretations from
>Hiroshima and Nagasaki for much of our fundamental data. 
>
>Apart from that, the dose to the most accurate dosimeter  is only a rough
>guide to a properly averaged whole body dose, allowing for radiation
>spectrum, body orientation, partial shielding etc.
>
>The true value of personal dosimetry is to indicate that good practices have
>been followed. Adding the numbers together for year after year tells you
>little more.
>It is unfortunate that lawyers and others, who should know better, think
>otherwise.
>
>David Perry
>
>Dr David R Perry
>Radiation Protection Adviser
>Health & Safety Group R12
>Rutherford Appleton Laboratory
>Chilton, Didcot, Oxon OX11 0QX, UK
>Tel: +44 1235 445314  Fax: +44 1235 445226
>
>The most important leg of a three-legged stool is the one that's missing.

------------------------------------------------------------
Christopher H. Clement
Scientific Specialist / Radiation Protection Program Manager
Low-Level Radioactive Waste Management Office
Atomic Energy of Canada Limited
clementc@aecl.ca