the function of -70 for X-ray film

[David N. Levy]

In article <4788j4$5l4 at elna.ethz.ch>
Sasha Kraev <kraev at bc.biol.ethz.ch> writes:

> David, I felt like responding to the other, not entirely accurate 
> statement, that was more about the screen rather than the emulsion.
> This question belongs to a newsgroup alt.photo.hobby or something like,
> however, I am not sure that it takes exactly two hits to make a 
> development centre in a silver grain, as the mechanism of reciprocity 
> failure is outside my profession. However, perhaps you know why the
> films like Reflection can be ( according to NEN-DuPont's ad )
> exposed at RT and still are as sensitive as their old counterparts, 
> exposed at -70 C?
> Regards,

I do not know.  However, in astrophotography (where detection of very
faint objects is desired), one can treat film with certain gases prior
to exposure to achieve the same (temporary) effect as -70¡ treatment.
This is called "hypering" the film.  So it is possible (and, again, I
have not looked into this) that some commercially available films have
been so treated.  Are these extra-sensitive films very perishable?  If
so that would be an indication that they have been chemically treated
in an analogous manner.

David N. Levy
Division of Molecular Genetics
Dana-Farber Cancer Insitute
Boston, MA 02115
david_levy at dfci.harvard.edu