Re: Efficiency Determination

[Wes Van Pelt <VanPeltW@mail.IDT.net>]

Julia Sober wrote:
> 
> 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

Dear Julia and Radsafers,

Ludlum Measurements, Inc. lists the counting efficiency as 2-pi rather
than 4-pi.  I believe most people mean 4-pi counting efficiency when
they speak of counting efficiency.  Thus, if Ludlum gave a figure of
60%, you would expect to measure about 30%.

There is even more confusion in the simple term "counting efficiency"
when the abundance of emission is different from unity.

I recommend that we all use the term "counts per disintegration" instead
of "counting efficiency". For a specified rationuclide, c/d is fully
defined and without confusion.  Any comments?

cheers, Wes
-- 
Wesley R. Van Pelt, Ph.D., CIH, CHP                   KF2LG
President, Van Pelt Assoc., Inc.      vanpeltw@mail.idt.net
Consulting in radiological health and safety.
"TIME, its what keeps everything from happening at once."