[ RadSafe ] surface emission rate,surface DPM from 27 pCi Tc-99

Geo>K0FF GEOelectronics at netscape.com
Sun Dec 16 12:50:29 CST 2007

Forgive my inexperience. One more attempt to phrase the question so it won't
be misunderstood.

I have a 27 pCi Tc-99 test disc which is electroplated onto a stainless
steel disc.

How many beta particles per minute are expected to leave the front surface
of the disc?

Disregard self-absorption, half-life, counting error, confidence level, and
systematic error. Most of that has nothing to do with this calculation

By knowing the expected beta emission rate, and then measuring the actual
detected rate by the sensor, the
beta efficiency at the Tc-99 energy for that sensor can be calculated.

 Reply if you care to, to

 George Dowell at

 GEOelectronics at netscape.com

PS whatever it takes, I will get technical discussion going or RADSAFE, it 
is part of the charter of Radsafe. I will make some mistakes along the way, 
much as many of our members would do. Unlike them, I have the thick skin to 
muddle thorough it and take the heat from a FEW retired cynics. I will make 
a way for them. There are those of the members that know everything already, 
then there are the rest of us, the vast majority probably.

----- Original Message ----- 
From: "Glenn R. Marshall" <GRMarshall at philotechnics.com>
To: "Geo>K0FF" <GEOelectronics at netscape.com>; <radsafe at radlab.nl>; "Franz 
Schönhofer" <franz.schoenhofer at chello.at>
Sent: Sunday, December 16, 2007 11:58 AM
Subject: RE: [ RadSafe ] surface emission rate,surface DPM from 27 pCi Tc-99


Dpm is a measure of the amount of radioactivity present.  If there is 60 dpm 
of radioactivity present on the surface of an object, then that is how much 
radioactivity is there.  It's a fixed value and it's present whether 
detected or not.  There is no such thing as 2-pi dpm of 4-pi dpm.  2-pi and 
4-pi, in the case of radiation detection, refer to the emission rate of 
radiation (in this case beta particles) due to the decay of radioactive 

The premise for your argument is incorrect.  You should refer to NUREG 1507 
or ISO 7503-1.


Franz says:" Furthermore I would have hoped that Mr. KOFF knows the
difference between
dpm (disintegrations per minute) and cpm (counts per minute). Obviously he
does not. "

*Franz, DPM or disintegrations per minute can be 2-pi steradian, or 1/2 of a
sphere, or 4-pi steradian or both halves of a sphere.

DPM is determined by activity level multiplied by probability of emission
for each radiation component of a nuclide. CPM is COUNTS per minute, which
is derived as the product of source DPM, subtended angle, probe efficiency,
and deadtime correction. CPM also has other meanings. George

Franz says:" Having worked more than thirty years on the determination of
radionuclides I
can assure everybody, that there is no interest in "how many particles are
leaving the test disc, but the most important analytical question is, what
the efficiency (both chemical and counting) is in order to translate cpm
into dpm. Am I missing something? This is the task of radionuclide
determination since probably 100 years!!!! "

*Franz, yes you are missing the whole point of the measurement. Yes it does
have uses. George

Franz says:" I would not be surprised if you would still not understand how
silly your
question was and even more that you insist on your less than amateurish
opinion. I do not expect that you will refrain from those silly postings. I
do not hopte that you will bother RADSAFE in the future. "

*Franz, hope in one hand..............

I'm here to share what I can, but especially to learn. That is supossed to
be, at least in part, the charter of this chat board. George

Best regards,


Franz Schoenhofer, PhD
MinRat i.R.
Habicherg. 31/7
A-1160 Wien/Vienna

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