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[radcon@sprynet.com]

T all fellow radsafers:
         I need some help on some technical issues.  In NUREG/CR-5489 there is a 
formula for MDA for instruments using an integrated count for a preset time:
 
 2.71 + 4.65 x sqrt of Background Count Rate x count time
___________________________________________________________
    count time x efficiency x active probe area (cm2)/100


I have been told that this formula is incorrect.  Is it??  If so then what is 
the correct formula??

Also I am going to use a Ludlum Model-3 with an attached 2" x 2" NaI detector 
for release surveys of outside ground areas for a decommissioning project (meter 
reads in CPM).  Main radionuclides Co-60 and Cs-137.  The MDA formula for this 
type of instrument is a 25% or 50% increase in the audible count.  Regulators 
have pointed out that this is a MDC calculation because probe area and 
efficiency are not used in the calculation.  My question is can the MDA be 
calculated??? If so, how??? Again I am scanning outdoor ground surface area 
(some gamma logging too) they (the regulators) want to know how many CPM above 
background relates to pCi/gram.  I think the geometry and type of survey make it 
a mute point and really make it a qualitative (go-no go) type of instrument.  
Any help in these matters would be greatly appreciated.  
reply to:
radconpro@aol.com
Dan