# Homework Help: Beta particle counting efficiency?

1. Jul 27, 2007

### wendo

Beta particle counting efficiency??

Hi!

Can anyone tell me what counting efficiency means? For example if it's put into a question as: "shielded beta counter with 85.7% counting efficiency, 845 counts are accumulated in one week" what does it mean?

How I understand it so far is that it's the ratio between the number of particles counted : # of particles that's actually emitted.... is this correct??

Thanks!!

2. Jul 27, 2007

### Astronuc

Staff Emeritus
Counting efficiency (of the detector) is the ratio of pulses detected to the actual events.

If one 'detects' 900 pulses when 1000 beta particles entered the detector, then the efficiency is 900/1000 or 0.9 or 90%.

Then there is also geometric effects, i.e. how many particles which are emitted from the source actually impinge on the detector. Then there is the effect of particles being absorbed by the media (between source and detector) and detector structure which will not be counted.

Is one asking for overall efficiency or counting efficiency of the detector?

Here is a good site for reference -
http://hps.org/publicinformation/ate/cat1.html

3. Jul 27, 2007

### wendo

The question gives the counting efficiency and overall asking to calculate the age of a piece of wood.

So in this case if counting efficiency is 85.7%, and 845 counts are accumulated in one week, then

.857=845 per week/# of beta particles actually emitted
=986 beta particles that are actually emitted per week?

Can this be used as the decay rate?

4. Jul 27, 2007

### daveb

Yes, when a problem says the counting efficiency is some number, it usually takes into account all aspects that affect efficiency (nuclide, energy, geometry, materials, etc.). You are correct in that 986 is the number of beta particles emitted per week, and his can be used to determine activity.

5. Dec 27, 2011

### mmiller

Re: Beta particle counting efficiency??

yes it is 986 beta particles per week. We had a similar problem in our testing environment while working on a new particle counter for the automotive industrie.