the function of -70 for X-ray film

[John R. Thompson]

Stephen Lessnick <stevel at ucla.edu> wrote:


>1)  Why would one expose 35S sequencing gels at -70 degrees in the first 
>place since they don't possess enough energy to make the enhancing screen 
>worthwhile.  On the other hand, soaking the gel in salicylate or PPO 
>would provide the enhancement effect, and then I believe it would make a 
>difference to expose the gel at -70.
>
Use of a screen is not the only reason to expose at -70.  The film
emulsion itself retains an image better at -70.  Thus irrespective of
whether or not a screen is used, there is advantage to be gained by
exposing at -70.

Regards,
John R. Thompson
Merck Research Labs