ESTIMATES OF AUTORADIOGRAPHIC EXPOSURE TIMES WITH 32P

Optimal exposure times must be empirically determined, but the following intervals are offered as a guide. In these cases, radioactive decay was measured on a Ludlum model 3 survey meter with a 44-3 detector, where 1 mR/hour is approximately 2500 counts per minute.

For genomic DNA, cpm are usually at background. Expose a minimum of 4 days.
For cloned DNA, use the following chart to estimate exposure times:

    CPM just above membrane Exposure Time
    < 0.2 K Overnight
    0.5 K 3-5 hours
    1 K 30 minutes
    3 K 20 minutes

In the dark room, place a sheet of X-ray film on top of an intensifying screen, then place the hybridization membrane on top of the X-ray film facing the film. The hybridization membranes are pre-wrapped in cellophane. Close the film cassette, wrap it in foil to prevent spurious light leaks, label the outside and expose in a -7 0°C freezer.
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Copyright 1993, 1996, and 1997 by Mark Barton Frank, Ph.D.
Proper citation for data acquired from this document is: "Frank, M. B. Estimates of Autoradiographic Exposure Times with 32P. In: Frank, M. B. ed. Molecular Biology Protocols. (http://omrf.ouhsc.edu/~frank/autorad.html). 1997. Oklahoma City. Revision Date: October 2, 1997."