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Re: [Phys-L] Bayesian Inference in Half-Life measurement



bc,

Yes, the stability on the instrument over several days is another
systematic source of error.
Daily fluctuations in cosmic background is another. As are some very
subtle weather dependent changes in radon levels.

All good points. Still looking for the right way to extract the maximum
amount of information from the data without arbitrary choices in the
analysis.

Paul


On Wed, Sep 22, 2021 at 6:09 PM bernard cleyet <bernard@cleyet.org> wrote:



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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