RE: [APML] To freeze, or not (Was: The good Supra 400pricereduction...)

["Greg Hartke" <ghartke@earthlink.net>]

A little over 25 years ago I was studying cosmic rays for my senior thesis
as a physics major in college. My experimental work was 3 fold: I designed
and built coincidence counters for studying showers, I designed and built an
expansion cloud chamber for photographing cascades of secondary particles,
and (germane to this discussion) I got a stack of film specifically for the
purposes of studying cosmic rays. (I didn't have time to sleep much,
either.) During that period, Kodak (at least I think it was Kodak) was still
active in making films for scientific usage and they made a specific film
for recording cosmic rays. You'd buy a stack of it and let it sit unexposed,
then after a period of time you'd develop the sheets. Keeping track of the
sheets was a nightmare (this didn't work out that well - I was too young and
hurried) but I can remember studying them under a stereo-microscope. The
memory is a little fuzzy by now but I seem to recall that cosmic ray tracks
(really secondary tracks, of course; the primaries didn't get to the bottom
of the atmosphere) were almost stellar but continued through many layers of
the stack. An experienced worker (not me) could determine things like the
nature and energy of the particle that made the trace. As far as I know this
kind of technique isn't used anymore but there was a time when it was all we
could do.

The point is that cosmic ray hits on film are going to be more like
point-noise rather than streaks.

Greg Hartke
Sykesville, MD

> -----Original Message-----
> From: astro-photo-bounces@seds.org
> [mailto:astro-photo-bounces@seds.org]On Behalf Of Philip Perkins
> Sent: Thursday, May 08, 2003 7:23 PM
> To: Discussion of Film Astrophotography
> Subject: Re: [APML] To freeze, or not (Was: The good Supra 400
> pricereduction...)
>
>
>  From what I have seen the effects of outdated film are indeed increased
> fog - chemical fog, and less sensitivity to emission spectra.  The OIII
> response seems to go first, followed by the Ha response, and what Ha
> response remains records as a muddy brown colour.  Stars still
> record, but
> stars are broadband points of light and so could be expected to "punch
> through" mild fogging.
>
> I am not so sure about fogging due to cosmic rays - we know that CCD
> detectors record them but do we know for certain that film records
> them?  Still, so little in known about cosmic rays, but since their
> appearance on CCD detectors is so characteristic, one might expect
> something analogous on film, even if only a "blob" or fuzzy
> streak of mild
> fogging, but I don't think any evidence has been seen has it?  I don't
> think the broad fogging that occurs across an entire film (due to aging)
> can be attributed to cosmic rays can it?  Isn't that far more
> likely to be
> due to chemical fog?
>
> --Philip
>
> At 14:28 08/05/03 -0700, you wrote:
> >Alan, I have yet to see a cosmic ray hit show up on my old film when
> >developed.  With a CCD you have a definite streak or dot.  Film
> may simply
> >just fog up.  Kodak adds water to film to increase the
> reciprocity failure
> >to keep it from self exposing in the cartridge while on the shelf from
> >THERMAL energy.  Apparently the molecules bouncing about will expose the
> >film grains.  In the freezer, this of course is greatly slowed to the
> >point film can last 10  years or more.  Some food for thought.
> >
> >Chris Schur
>
>
> Philip Perkins - philip@astrocruise.com
> Wiltshire UK & Luberon France
> Astrocruise - http://www.astrocruise.com
>
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