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

[bernard cleyet <bernard@cleyet.org>]

> 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