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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 -70°C freezer.
来自Lab of Dr. Mark Barton Frank, Oklahoma Medical Research Foundation
http://omrf.ouhsc.edu/~frank/AUTORAD.html
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