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

garyi at trinityphysics.com garyi at trinityphysics.com
Fri Dec 14 12:20:50 CST 2007

```Since he did not explicitly discount the back scatter from the substrate, I would guess that the
actual number is about 10 to 20% higher than the 60 k/s figure, perhaps 66 to 70 k/s

-Gary

On 14 Dec 2007 at 18:54, Rainer.Facius at dlr.de wrote:

Subject:        	AW: [ RadSafe ] surface emission rate,surface  DPM from 27 pCi
Tc-99
Date sent:      	Fri, 14 Dec 2007 18:54:48 +0100
From:           	<Rainer.Facius at dlr.de>

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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

________________________________

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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