Background counts...

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..
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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:oops:
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Lvl 37 Alchemist
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.
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.
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.
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.