Re[2]: Drill Scenario

[tdc@ehssun.lbl.gov]

>The dose rate on the lateral surface of an irradiated fuel bundle that has
>decayed for >30 days is in the neighborhood of 5E5 to 1E6 R/hr contact.


>1/4 inch    = 1E6 R/hr
>8 inches   =  33,750 R/hr 48 sec
>~5 feet     4200 R/hr  6.4 minutes
>~ 21 feet  1000 R/hr  27 minutes  

You know - this is a very good example of the ridiculous use of the
meaningless quantity "contact dose"!

It really is not very useful yet its use persists in the industry.

For the "contact dose" to represent the reading at 1/4 inch the detector
assembly would have to be only 1/2 inch thick.  Not too many dose
responding detectors are that small that are not also influenced by local
scatter factors too!

It is really hard to know WHAT distance so called "contact" measurements
represent and they certainly don't estimate REAL contact risks like skin
dose.

This is instrument misuse at best.

When you use such a measurement at an assumed and inaccurate small geometry
and then try to extrapolate that out to very large distances - the errors
are enormous.

The 30 cm - or better yet 1M readings are so much more meaningful and
accurate.  Such measurements lend themselves well to far field
extrapolations.

Ted de Castro
tdc@ehssun.lbl.gov
University of California Lawrence Berkeley Laboratory
Bldg 90 Rm 0026B
Berkeley, CA 94720
(510) 486-5256
(510) 486-6939 - FAX