Why freeze autorads?

Stephen C. Dahl stebby at welchlink.welch.jhu.edu
Thu Nov 21 13:09:21 EST 1996

: : Samuel C. Blackman wrote:
: : >My labmates and I, obviously with too much time on our hands, were 
: : >wondering why we put our 32P-labelled autorads in the freezer at -80C.
: : >Our advisor hypothesized that the low temp. promotes a more "focused"
: : >autorad, but without a good explanation for that.  The decay equation
: : >has no mention of temperature, so we're stumped.  Any ideas?
: : >

Warren Gallin wrote:
: :     The short answer is "reciprocity failure".  At low exposure rates the
: : effect of a single radiation event on a single halide crystal in the film
: : emulsion will  often decay before subsequent stabilizing events hit.  Ths is
: : reflected in the film reciprocity curve, which shows a non-linear
: : relationship between exposure and optical density at very low temperatures. 
: : The decay of single event effects is temperature dependent.  Thus, by
: : lowering the temperature, you prevent the decay and increase the sensitivity
: : of the film.  You can get the same effect by pre-flashing the film.

William Tivol wrote:
: Dear Warren & Sam,
: 	The short answer is OK for exposure of film to light; however, 32P
: is a high-energy (1.7 MeV endpoint) beta-emitter.  X-ray film or other elec-
: tron sensitive film needs only one event to render a grain developable.
: It should be fairly easy to do the relevant experiment if you really 
: have so much time on your hands.

First, Sam, you and your lab mates should be commended.  There is too 
much cookbook and kit-based science going on without people understanding 
what or why they are doing something.  However, rather than doing the 
experiments as suggested above, may I counter-suggested some "light" 
reading?  A number of scientists have done the work for you and the 
papers are good to have around for reference or teaching others.
Most prolific has got to be Ronald Laskey out at the MRC.  As a starter 
may I suggest:

Laskey and Mills, FEBS Letters (1977) Vol. 82 pp 314--316
Laskey, Methods in Enzymology (1980) vol. 65 pp 363--371
Bonner and Laskey, European J. of Biochemistry (1974) vol. 46 pp 83--88

Also check out 

Swanstrom and Shank, Analytical Biochemistry (1978) vol. 86 pp 184--192
Randerath, Analytical Biochemistry (1970) vol. 34, pp 188-205

And for those who prefer the Reader's Digest version, Kodak has a very 
nice booklet which I'm sure they will send you for free if you point out 
how good their products have been to your quality of life.  Ask for:

Autoradiographic Detection Principles

Customer service for Kodak used to be  1-800-225-5352, but this was 3 
years ago.  Ask for the Life Science Imaging Technical Services Department.

All of these references are concerned with getting an autoradiographic 
image on film.  The issue of temperature is dealt with within the text so 
you'll have to do a little hunting, but I guarantee you'll learn 
something new.

Then get back to work :o)


Stephen Dahl
Johns Hopkins University

>all my babbling is my own and not that of my employer<

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