intensifying screens

Klaus Salger salger at
Wed Jun 19 17:08:02 EST 1996

Robyn Wallace wrote:
> I have a few questions about exposing P-32 labelled DNA to x-ray film.
> How do the intensifying screens in the cassette work, and do you need two?

The screens will fluoresce when excited by radiation. If the fluorescent
light can pass your sample (membrane) 2 screens will give stronger
signals on the film.

> Why does putting the cassette at -70C increase the intensity?

There is an unstable intermediate stage after the film is hit by
radiation or light. It has to be hit a second time in order to give a
signal. This intermediate is more stable at low temperature so the
probability to hit an intermediate is increased.

Hope this helps a bit

Klaus Salger                phone : +49 (0)89 5902 -502
Zoologisches Institut       FAX   :                -450
AG MacWilliams              e-mail: salger at
Luisenstr. 14               
80333 Muenchen


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