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

Rainer.Facius at Rainer.Facius at
Fri Dec 14 11:54:48 CST 2007

Assuming that DPM stands for decay per minute, my answer would be:


27*10^-9 Ci * 3.7*10^10 decays/s/Ci = 999 decays/s 


Since Tc 99 is a pure beta emitter, each decay emits one beta particle.


Hence 999 beta-particles/s leave the "plane" onto which the Tc 99 has been dispersed (with 294 keV/particle).


999 beta-particles/s * 60 s/min = 59940 beta-particles/min (DPM?)


Ignoring all the stated corrections, including reflection from the stainless-steel support, half of this number, i.e. 30000 beta-particles/min, leaves the test disk into one half-space.


So what is/was the problem; what did I/we miss or misunderstand? :-) 




Von: radsafe-bounces at im Auftrag von Geo>K0FF
Gesendet: Fr 14.12.2007 16:39
An: Geo>K0FF; radsafe at
Betreff: [ RadSafe ] surface emission rate,surface DPM from 27 pCi Tc-99

In case there is some confusion or a problem in translation, the information
requested is the 2 pi beta emission rate from the source delineated below.

Another way of stating it is: the total number of beta particles coming from
the front working surface of the disc.

Forget about self absorption, counting error, confidence level, and
systematic error.

This is not a trick question. To determine the beta efficiency of a probe,
one needs to know how many particles are leaving the test disc.

Reply if you care to, to

George Dowell at

GEOelectronics at

The calculations will be posted here after a short time.

George Dowell
New London Nucleonics Lab

----- Original Message -----
From: "Geo>K0FF" <GEOelectronics at>
To: <radsafe at>
Sent: Tuesday, December 11, 2007 7:45 PM
Subject: [ RadSafe ] DPM from 27 pCi Tc-99

> What is the surface DPM of a 27 pCi Tc-99 electroplated disc source? The
> substrate is stainless steel. (by calculation only please)
> George Dowell
> New London Nucleonics Lab

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