Re: Efficiency for detection of Tc-99m

[William V Lipton <liptonw@dteenergy.com>]

A rule of thumb for a frisker is that its efficiency is 1% for photons with
energy 100 keV or greater, and 10% for beta particles (including conversion
electrons) emitted with an average energy of 50 keV or greater.  The major
radiations from Tc-99m, using ICRP38, are:

radiation        abundance (%)        energy (keV)
gamma            88.9                        140.5
ce                    8.79                        119.4

Thus, I would expect the overall frisker efficiency to be approximately:

[(0.01)*(0.889)] + [(0.1)*(0.0879)] = 0.018 = 1.8%

This does not account for any Mo-99 breakthru.  Since Mo-99 has a higher beta
abundance, it would have a higher detection efficiency.

The opinions expressed are strictly mine.
It's not about dose, it's about trust.

Bill Lipton
liptonw@dteenergy.com

"Jacobus, John (OD)" wrote:

> Can anyone give me a reasonable detection efficiency for measuring Tc-99m
> surface contamination using a GM pancake type probe?
>
> -- John
>
> John Jacobus, MS
> Health Physicist
> National Institutes of Health
> Radiation Safety Branch, Building 21
> 21 Wilson Drive, MSC 6780
> Bethesda, MD  20892-6780
> Phone: 301-496-5774      Fax: 301-496-3544
> jjacobus@exchange.nih.gov (W)
> jenday@ix.netcom.com (H)
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