-----Original Message----- From: Abd ul-Rahman Lomax > This is what I expect to see: I'll be lucky if I register on the film one neutron track per several minutes, maybe ten minutes, average....The key to the film is getting the film very close to the source, so neutron levels on the level of one per minute can be accumulated. Now, if I have a gamma detector, how do I know that the gammas came from the source? Couldn't they come from cosmic rays? Consider how much background there is on an ordinary Geiger counter!
Yes good point - the differential rate may be too low - i.e. to show anything significant above background. But we should be able to guesstimate that in advance. The variable to consider as to whether the effort would add anything - is the effective capture rate of the film vs. the meter. The film would have a known cross-section for capture, whereas a thin Gd plate of the same area size would capture essentially 100% of neutrons. It could even be placed behind the film to pick up those that passed through if the film capture rate was low. In general terms, if the background rate (due to cosmic rays etc) were say 10 counts per minute, and we estimate the cell rate at 5 counts, then 15 would show on the meter when the cell was operating, and that might be considered statically significant. If there were 5 counts/min coming from the experiment and only one was captured by the film, then the addition of the Gd + GM meter might be worth the efforts since it adds a confirmation - plus, it is all probably predictable in advance. IOW you would need more information before moving forward, but there is the likelihood that the information is 'out there'. Jones
