[ RadSafe ] Clarification : Validity / Usefulness . . .

Earley, Jack N Jack_N_Earley at RL.gov
Wed May 2 13:50:30 CDT 2007

I knew something was bothering me about this question--it depends on the
purpose of your sampling. Are you looking at an environmental release
sample set, something applicable to daily operations, or confirmation of
non-detectability? That has to determine your reasons for inclusion or
exclusion. For example, if I find a radiation area in a parking lot I'm
going to shut down a calibration facility until they hang lead shielding
(been there, done that), and I have less concern about the variability
on the instrument I'm using (assuming it's properly calibrated).

If I'm looking at soil samples to release an area for unrestricted use,
or verifying the integrity of sealed sources, my criteria go way up. If
I'm not happy with the accuracy of my results, I can change
instruments/detectors for more accuracy.

On the other hand (the economist side of me), I can also disregard a 350
mR/h exposure rate when determining the collective dose for a given job
(12 mR/h without the outlier) --its presence in the sample doesn't
necessarily make it significant.

Jack Earley
Health Physicist

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Pete_Bailey at fpl.com
Sent: Wednesday, May 02, 2007 4:23 AM
To: radsafe at radlab.nl
Subject: [ RadSafe ] Clarification : Validity / Usefulness . . .

Thanks to all that have responded....

I'm not after guidance on sampling frequency or testing if two positive
measurements are different . . .

What I'm after (and many spoke around ,but didn't directly answer):

In your world i.e., by your procedures
would you consider any one of the following different pairs of R +-r  to
be 'not useable'  for comparison to whatever ( a limit, a prior sample,
etc) ?

a.    110  +- 140

b.    480 +- 140

c.     270 +- 140

d.    630 +- 140

If your procedure would have you consider a pair as 'not useable', what
is the basis of your procedure's decision process ?

As far as 'difference' of two positive results, I am very much aware of,
familiar with, the "z score" , "zeta test"; it is standard stats.

BUT "by your procedures", what do you do when one of the two is  "less
than (a number) " and you don't have a standard deviation of the LLD
and the other is  R +-r   ( with R not being far from a typical LLD
  - do you use the "z score test" & assume  r  to be applicable to the
LLD value ?

Hopefully, the above clarifies what I was attempting to ask

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