[ RadSafe ] Fwd: Cs-137 beam calibrator output

[Dahlskog, Leif]

As Chris mentioned, perhaps the error lies in the quoted original activity.  Does the source certificate provide the uncertainty in the activity measurement ?

Another though, any other objects/nearby surfaces in the beam.

regards

Leif Dahlskog 
Senior Health Physicist 
Radiation Health Branch 


-----Original Message-----
From: radsafe-bounces at agni.phys.iit.edu [mailto:radsafe-bounces at agni.phys.iit.edu] On Behalf Of Chris Alston
Sent: Tuesday, 23 September 2014 8:31 AM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: [ RadSafe ] Fwd: Cs-137 beam calibrator output

Clayton

I think that the key to the conundrum lies in the term "nominal".
Some suppliers of sources to the manufacturers of these devices are not as careful as they might be in quantifying the activities.  You might try estimating the half-value thickness for the beam, as a way of getting a handle on how hard it is; i.e., how much is 662 keV, and how much is Compton garbage.

Cheers
cja
---------- Forwarded message ----------
From: clayton bradt <dutchbradt at gmail.com>
Date: Mon, Sep 22, 2014 at 7:00 PM
Subject: [ RadSafe ] Cs-137 beam calibrator output
To: radsafe at health.phys.iit.edu

My apologies if this duplicates an earlier post. Having received no bounce notice for the previous one, I am re-sending from a different email account.

********

Original post:


I’ve been reviewing data for a beam calibrator containing a Cs-137 source with nominal activity 600 mCi on 1/18/2005.  The measured output at 1 meter along the beam center line was 0.2443 R/h on the same date.  Comparing that with the calculated exposure rate at 1meter from a 600 mCi point source I get 0.193 R/h, assuming a Gamma constant for Cs-137 of 0.322 R/h at 1 meter
per Ci.   I am surprised at such a large difference (27%) between the
theoretical value and measurement.  Should I be?  I know that scatter from the collimator will affect the actual exposure rate, but this much?



Any help from people with more experience with exposure rate calibrations on this list will be most appreciated.
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