Simple Question about Intensifier screens

[Dr. Peter Gegenheimer]

On Fri, 29 Aug 1997 16:00:23, "R. John Lye" 
<rjl6n at uva.pcmail.virginia.edu> wrote:

> Mathias Drexler wrote:
> > 
> > I am wondering, why intensifier-screens are working better at -80°C.
> 
> Its not that intensifier screen work better at -80 (as far
> as i know).  It is that film gets more sensitive to weak
> signals at low temperatures.  It takes two photons to activate
> the silver grains in film, and the second photon must arrive
> before the excited state induced by the first photon decays away.
> The low temperature porlongs the lifetime of that excited state,
> and therefore makes it more likely that a second photon can
> arrive to do its work.
> -- 

Since the excitation comes from the screen, the low temp really is 
working on the screen. This subject was discussed before, with some 
more imformed comment on the film vs screen response. I don't recall
all the details, unfortunately. 

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