Re[2]: ?NVLAP category V C

["GOLDIN, ERIC" <goldinem@songs.sce.com>]

     John/Sandy,
     
     Here's my two cents...
     
     If your radiological environment includes both low and high beta 
     spectrum (ie. Sr/Y and Tl) then you may need to redesign your 
     badge.
     
     The design requirement for distinguishing beta energies requires two 
     elements, one at less than about 20 mg/cm2 and another less than say 80 
     mg/cm2.  The ratio of these two elements is used to determine the 
     average beta energy and the appropriate beta energy correction factor 
     for any given exposure.  Of course, another gamma-only element is 
     needed and this is reasonably met by an element under the 1000 mg/cm2 
     filter.
     
     Your solution of using a midway response factor may be the only option 
     available to you.  If so I know of no magic to get blood out of a 
     turnip.
     
     Mike Russell, CHP
     Southern California Edison
     russelmj@SCE.com
     
     
     
     
     This response is based on a 4 element TLD, 2 elements of LiBO and then 
     2 elements using CaSO. The filtration is as follows, 7, 300, 300 and 
     1000. The primary basis should still be true for LiF, that the 
     Sr-90/Y-90 will penetrate even a 1000 mg/cm^2 filter, where the Tl-204 
     will only penetrate a 7 mg/cm^2 filter. Therefore, if this is also 
     true for a pure 3 or 4 element LiF TLD, with some appropriate 
     filtration, the decision matrix is easy. If there is Sr-90, it can be 
     seen on all the elements. If it is a Tl-204 exposure, it will only be 
     seen on the 7 mg/cm^2 element, the others showing basically control 
     background response. This is also true for Category VII, which we also 
     test, and again, the mixture of Cs-137 with either Tl-204 or Sr-90 is 
     quite evident. 
     
     What you should be doing is to define the algorithm correction factors 
     for specific exposures to either the Tl-204 or Sr-90. Once you 
     dtermine the energy of the source, the correction factor will be 
     accurate within a small % deviation from true exposure. There is no 
     reason to be high on one and low on the other. Test and let the 
     algorithm correct for your response of the dosimeter.
     
     If this basis is not true, then I'm sure someone else will jump in 
     here, discussing the LiF response.
     
     Sandy Perle
     Supervisor Health Physics
     Florida Power and Light Company
     Nuclear Division
     
     (407) 694-4219 Office
     (407) 694-3706 Fax
     
     sandy_perle@email.fpl.com
     
     HomePage: http://www.lookup.com/homepages/54398/home.html
     
     
     
______________________________ Reply Separator _________________________________
Subject: ?NVLAP category V C
Author:  radsafe@romulus.ehs.uiuc.edu at Internet-Mail 
Date:    12/4/95 1:57 PM
     
     
I am writing my MS thesis on a LiF dosimeter design.  Is anyone testing 
in the beta mixture category using a standard 3 or 4 element badge?  I 
can just get by using a response factor midway between that for Sr/Y-90 
and Tl-204, but am naturally overresponding in one case and 
underresponding in the other.  How are people handling this category?
     
My badge does not have filtration to distinguish the beta energies.  The 
badge is designed to handle both neutrons and photons as well, so three 
elements are filtered with Cu, Cd, and plastic.  A mylar window covers 
the sole thin beta-detecting chip.    
     
Please respond to zummo@gene.com
     
Thank you in advance for the help.
     
     
     
John Zummo, RSO
EH&S - MS 71
Genentech, Inc.
460 Point San Bruno Boulevard
South San Francisco  CA  94080-4990
     
(415) 225-2959
(415) 225-5008 (fax)
     
zummo@gene.com