[Halld-pid] PMT test results question

[Alexander Ostrovidov]

Hi Beni,

I have tried both of your suggestions - going to much lower HV
and using light guide. Unfortunately, the only effect achieved was 
making the signal smaller. The large spread of signals on the scope 
from Am241 source was still there. At about 1500V, most of the
signal already went below 30mV threshold I set for scope triggering.
Once every few seconds, I would see a large and varying pulse (supposedly, 
from cosmic rays) and that's about it. Nothing resembling a stable large
pulse from the Am source anywhere from 1750V to 1300V, but only a small
signal with large spread.

Sasha

On Tuesday, October 30, 2012, Beni Zihlmann wrote:
> Hi Sasha,
> 
> I would expect that the source should produce thousands
> of photo electrons in the PMT. So the signal should be very
> very very large.
> Can you reduce the HV by a lot? like  running at 1400V or so and see
> what that does to the signals in the PMT?
> Also you could put a light guide in between the source and the PMT to
> make sure that the very low UV part is absorbed before hitting the PMT?
> 
> cheers,
> Beni
>