Jonathan B. Marder
MARDER at agri.huji.ac.il
Sun Jun 30 01:45:15 EST 1996
<Pine.A126.96.36.1990626133354.45748C-100000-100000-100000 at umabnet.ab.umd.e
Stephanie Tucker <stucker at umabnet.ab.umd.edu> wrote:
>My best answer -
>The intensifying screens are activated when exposed to -70C
It's not a question of activation, rather efficiency of the
scintillation process. Low temp also slightly increases the sensitivity
of the film.
>You DO NOT need two of them, just put one on one side of
>the gel, and a piece of film on the other side. This procedure can be
>substituted for merely developing 32P gels at room temp., with no
I believe this to be wrong. The screen turns fast beta emissions to
light, thus (for 32P) is most effectively used to trap radiation which
has passed through the film. This implies putting gel and screen on
opposite sides of the film. A second screen can be used on the other
side of the gel (to trap radiation going away from the film). However,
light emitted is a gel thickness away from the film leading to fuzziness
of the image.
>This may suffice if you have a screaming hot gel.
If the gel is really hot, plain autoradiography gives the sharpest image
- any fluorograsphic technique, including screens, reduces resolution.
>INtensifying screens are good if you are looking for something barely
>there, or if you are using 35S. Just remember, take the saran wrap OFF
>when exposing 35S gels!
Intensifying screens have little value for the low-energy beta emissions
from 35S. The radiation which makes it out of the gel is so low energy
as to be completely absorbed by the film. Also, any radiation in the
opposite direction would be blocked by the medium used to mount the
A nice trick for double-labelled (35S and 32P) gels is to arrange the
following: gel-film-film-screen. The film nearest the gel has both
images. The film nearest the screen has a strong image from the 32P only
(enhanced by the screen).
The most common means of amplifying 35S and other weak beta emitters is
to impregnate the gel with scintillant (PPO, salicylate several
procedures and/or commercial preparations available) before drying. This
traps beta particles within the gel matrix and turns them into flshes of
light which can then migrate out to the film.
Jonathan B. Marder , Department of Agricultural Botany
E-mail: MARDER at agri.huji.ac.il | The Hebrew University of Jerusalem
Phone: (08 or +9728) 9481918 | /\/ Faculty of Agriculture
Fax: (08 or +9728) 9467763 |/ \ P.O.Box 12, Rehovot 76100, ISRAEL
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