Re: Clarification: Efficiency for detection of Tc-99m

["David Whitfill" <DWhitfil@kdhe.state.ks.us>]

I have done several measurements with different sources for the gamma
efficiency for a pancake GM probe.  3-mm of aluminum was used as a beta
shield (distance from the source was measured from the top of the source to
the face of the detector):

c/d = counts per disintegration
All efficiencies 4 PI

Uniformly loaded Ba-133 silver zeolite cartridge (1-cm): 2.22 E-04 c/d
Note Ba-133 emits conversion electrons and the efficiency without the
aluminum was 3.04 E-04 c/d

Face loaded Ba-133 silver zeolite cartridge (1-cm): 2.67E-04 c/d
Without aluminum 5.59E-04 c/d

Uniformly loaded mixed gamma charcoal cartridge (Cd-109, Co-57, Ce-139,
Sn-113, Cs-137, Co-60, Y-88; 1-cm): 3.11E-04 c/d

Mixed gamma 13-filter air particulate composite (Gelman Type A/E 47 mm
glass fiber; Am-241, Cd-109, Co-57, Cs-137, Co-60; 1-cm): 6.82E-04 c/d

Cs-137 plastic disc source (1-cm): 9.09E-04 c/d

GRAND across all sources

AVG=4.18E-04 c/d
STDS=2.69E-04 c/d
Std. error of the mean=1.02E-04 c/d
N=7
MIN=2.15E-04 c/d
MAX=9.09E-04 c/d
Coefficient of variation=64.3%

Hope this helps!





"Jacobus, John (OD)" <JJacobus@exchange.nih.gov>@romulus.ehs.uiuc.edu on
01/21/2000 09:38:45 AM

Please respond to radsafe@romulus.ehs.uiuc.edu

Sent by:  radsafe@romulus.ehs.uiuc.edu


To:   Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
cc:

Subject:  Clarification: Efficiency for detection of Tc-99m


Please note that Tc-99m is used in nuclear medicine studies for in vivo
imaging.
It emits photons and conversion electrons.

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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