Re: Efficiency Determination

["Wesley M. Dunn" <WDUNN@brc1.tdh.state.tx.us>]

Julia,

I generated the following numbers are from my "typical" survey 
instrument (which happens to be a Ludlum) a few years back:

Relative Survey Meter Efficiencies 

 ISOTOPE SIDE_CLOSE SIDE_OPEN ONEXONE THIN_CRYS PANCAKE ENERGY        
       
 BACKGND <80        <60       2000    <300      <100                  
       
 CO-60   .23%       .25%      8.4%    2.5%      1.3%    1.33;1.17     
       
 NA-22   .20%       .25%      15%     5%        1%      1.27;.511
                                                        Beta .611     
 CS-137  .05%       .05%      5.3%    3.2%      .58%    .662          
       
 BA-133  .04%       .07%      21%     >21%      .35%    .356;.081
                                                        .303       
 CD-109                       3.7%    28%       .23%    .088          
       
 I-129                        2.4%    9.9%      .07%    .040          
       
 P-32               5%        0.5%    35%       40%     Beta 1.7       
         
For a pancake, I'd also expect about 7-15% for C-14/S-35.  
Efficiencies vary tremendously, even for the same probe model, so 
these should only be used as a rough estimate.

So, as you can see, the 35% isn't too far off.  That said, I'd suggest
you attempt to budget to get a beta source kit from one of the 
manufacturers.  It's a lot easier (and probably more accurate) than 
making your own sources.

Wes

> Date sent:      Tue, 26 Nov 96 11:23:09 -0600
> Send reply to:  radsafe@romulus.ehs.uiuc.edu
> From:           Julia Sober <T80JCS1@WPO.CSO.NIU.EDU>
> To:             Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject:        Efficiency Determination

> Dear Radsafers,
> 
> I have recently obtained a Ludlum Model 3/44-9 and am in the process of
> performing efficiency calculations for various isotopes in use at my
> facility, namely P-32, S-35, I-125, and C-14.  In determining efficiency, I
> plan to take a measured amount of each isotope, place it on a disc
> smear, determine the count rate, and perform the necessary
> calculations.
> 
> Yesterday the above method gave me a 30.6% efficiency for P-32.
> 
> I would like to know if this is within the expected range for this
> instrument and if this is an efficient (so to speak) method for determining
> efficiency.
> 
> I would also appreciate a list of expected efficiency ranges for the
> Model 3/44-9 for the isotopes I have listed if anyone is using similar
> instrumentation and has these numbers handy.
> 
> In Anticipation, 
> Julia Sober
> Acting RSO
> Northern Illinois University
> DeKalb, IL 60115
> 
> jsober@niu.edu
> Phone (815) 753-1093
> Fax (815) 753-0461
> 
*********************************************************************
Wesley M. Dunn, CHP                        512-834-6688
Deputy Director, Licensing                 512-834-6690 (fax)
(Texas) Bureau of Radiation Control        wdunn@brc1.tdh.state.tx.us
*********************************************************************