Background counts...

[Igor]

Question. When you do the background counts for RS, how long do you do it for? L093 suggests 1.40... I've got a physics teacher who says he's sure it's only a minute, or was at one point...

I'm watching some schools on YouTube, they only do it for a minute as well..

 

[Baldilocks]

Whatever L093 says.

 

[Igor]

Ok. Has that ever changed at all, then?

 

[chris vaudin]

I think the CLEAPSS guidance is the first time there has been advice on this, prior to that people chose their own interval. I always used to do 1 minute as a check as I could always remember that around 12 cpm was "normal" here. When the students did it, we used to run it for 5 or 10 minutes to smooth out a bit of the randomness.

OOPS, not quite right! See my later post

 

[Tonytech]

For CLEAPSs beta efficiency, leakage and contamination checks the background counts should be over one thousand seconds.

 

[seebee]

I think it says 1000s

 

[CovTech]

I think it says 1000s

1000s is for calibrating for the leak tests - it's over 17mins so probably want less for a lesson

If you're just doing it for a standard lesson on penetration then a 100s count should be fine

 

[Nick Mitchener]

L093 reduced the time for the test count, a couple of versions ago I think. My testing is way faster now. I still do a 1000 second background count though as I only need to do it once and I don't have to stand there while it is done.

 

[chris vaudin]

Aah, I beg your pardon, my memory isn't what it was. Indeed CLEAPSS say that you should run the background count for 1000 seconds for leak tests or calibration, but then divide by 10 to get the counts per 100 seconds. This is what has changed, we used to divide to get counts per minute.

 

[Phystech]

When I set up the GM counter before the lesson, I note the time and let it run. The teacher records the count when they come into the lab and the students work out the CPM. I only bring the sources into the lab once the students are settled.

 

[Glynis]

Doing the leak tests, it used to be count for 2 minutes and do the average for counts per minute. Now it's counts per 100 seconds with the original background count being done over 1000 seconds.

 

[Phystech]

I do our leak test with an Isopropyl alc, dampened cotton bud, wipe all round the castle, lid and source, also tap the source onto a dampened filter paper. Then check both together, for a 1440 minute run at 20 minute/sample. I also, check the integrity of the source with a mirror.