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

Rainer.Facius at dlr.de Rainer.Facius at dlr.de
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? :-)

Rainer

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Gesendet: Fr 14.12.2007 16:39
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
being
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 netscape.com

The calculations will be posted here after a short time.

George Dowell
NLNL
New London Nucleonics Lab

----- Original Message -----
From: "Geo>K0FF" <GEOelectronics at netscape.com>
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
> NLNL
> New London Nucleonics Lab

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