Re: IONIZATION CHAMBER, was ...

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Bob Sciamanda wrote:

> I withdraw this comment - for a truly current signal this does not apply!
> (Still learning!)
> -Bob
>
> > If you're going to convert that signal current into a signal voltage,
> > by letting it develop a pd across a "load" resistor, then you want
> > as high as practical a "load to source" resistance ratio.

The original message made sense to me, in principal, but not in
practice, unless the load resistance is very small. But the withdrawing
comment forced me to think. Is an ionization chamber a "truly current"
source? Does it deliver a constant current no matter how large is the
load? I suppose it does if the effective voltage V'=V(Battery)-i*R, is
high enough to collect all ions (no recombination). On the other hand
it is the collected charge per particle, not the current per particle, that
remains constant. Why? Because the speed with which ions are
collected is voltage-dependent.

I never heard about liquid ionization chambers described by Michael
Edmiston. How do they behave in terms of separating and collecting
ions? How large must the field E be to prevent the recombination?
(Is it much larger than about 100 V/cm for air at p=1 atm?) Why are
the liquid argon chambers more noisy than common gas chambers?
My naive expectation would be that they should not be more noisy
and that the only difference is in the smaller size (for the same energy
of stopped particles). Why should the dielectric medium (liquid argon)
be more noisy than gas or solid (Si)? I assume the detector was used
as a chamber, not as a proportional counter. Is it not true that under
such conditions most of the noise comes from the preamplifier?

Ludwik Kowalski