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On 2021/Sep/22, at 12:16, John Denker via Phys-l <phys-l@mail.phys-l.org>wrote:
We agree that "simply subtracting the background will sometimes
result in a negative number of counts".
That’s not the only problem.
If I understand correctly, if this is likely, that implies a rather small
counting rate, and, therefore, long times counting will be done; unless the
half life is too short. So long background counting, but the background
changes, is it diurnal? Or? Another project.
Any way; In my v. long time counting, I find sig diffs with counting
background for 200 minutes [1] separated by six and/or twelve hours. I’ve
considered counting the source and the background on two apparatuses. (~
two inches of lead shielding)
As I’ve posted earlier this is “junk” collected in filters.
Also I’ve noticed that the decay of mBa-137? end in a higher background
than the back. collected before adding the elution from the Cs-137 “cow”.
This is even after several days. So I conclude the separation using the
(is it?) ion exchange resin is not perfect. Next project is to use my SCA
to verify it’s Cs-137 “leakage”.
Later:
In an associated search, I find the Pasco version claims < 50 Bq/ml
leakage. I have an expensive dated calibrated Cs source, so I'll
calibrate one of my NaI detectors and verify. Maybe.
[1] The longest selected time on my The Nucleus 550 scaler-timer.
bc
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