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13792RE: [GPSL] Gamma Ray / X-Ray Detector Payload

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  • Barry Sloan
    Feb 14, 2014
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      NASA was concerned about film being fogged by radiation when they began sending cameras on manned flights, but found it wasn’t a problem. You could try the 3200 or 400 ASA films you mentioned and over develop them to push the ASA even higher, but each film type has a limited frequency response or radiation range over which it is sensitive and why special films are used for xray, infrared and similar applications. As for a dark room to package the film for a flight, you could buy (or possibly borrow) what’s used by photographers to load film into 4x5 view camera film holders or any other time film must be handled, like loading film into development tanks which is simply a light tight black bag with 2 openings for passing your hands through that fit tightly around the arm to prevent light leakage and a light tight zippered opening for getting the film, etc. in and out of the bag. Your biggest problem however will likely be finding a place that still develops film or a place to buy what’s needed to develop it yourself as few such places still exist with almost everyone now having moved on to digital photography, but your idea to contact your local dentist and get/use some Bitewing tabs is excellent. Not only are they sensitive to the radiation you wish to detect, but the film comes already packaged in a light tight pouch and your dentist will be able to develop them for you. I believe development of the film is fairly automated and not sure if the dentist has any control over the development time, but if he does I would send up at least 4 or 5 film pouches, only develop one to start and, if no fogging, start increasing the development time for each of the other pouches until fogging is seen, assuming there was some of course. I would double the last time used for each additional film. And if it takes longer than the usual development time to see fogging, I would then also process a film that wasn’t sent aloft for the same amount of time to confirm the fogging was due to radiation rather than from simply being over developed too long. The fastest B&W film I could get when I was in high school in the 60’s was 400 ASA which I used to use as 6400 ASA and develop myself in order to shoot high speed basket ball and similar indoor images for the yearbook using just the normal room lighting. I’ve long forgotten how much extra development was needed for each doubling of the ASA, but I found film could be over developed a fair bit and that the limiting factor wasn’t fogging, but the lack of contrast (i.e. the film density where exposed to light becomes increasing less black as the film is exposed less and developed longer).  Anyway, please report back if you proceed with the x-ray film as I would be very interested in knowing how well it works.  Something else you may want to consider doing, is to monitor sun spot activity and launch when extra high radiation levels are expected. We’ve included a Gamma / X-Ray Detector on a number of our recent flights for a UofA physics student and part of what he was doing was measuring the increase in radiation during a sun spot event.


      From: GPSL@yahoogroups.com [mailto:GPSL@yahoogroups.com] On Behalf Of Bill Ripley
      Sent: Friday, February 14, 2014 10:14 AM
      To: GPSL@yahoogroups.com
      Subject: [GPSL] Gamma Ray / X-Ray Detector Payload

      My wife and I have been brainstorming ideas for a student-built Gamma Ray / X-Ray Detector for the upcoming student HAB launch

      Typical lore has you putting very fast B/W film inside of a light tight box and flying it, then counting the zits on the developed photo.  This is a lot easier said than done, we think.  I have found some Illford B/W 3200 ASA film at my local "real camera store".  Then the problem becomes what do you do with it?  I thought about taking something like an oatmeal container, cutting it down to around 2" high and using it as a drum to put the film in.  I think you could cut a piece of film the length of the circumference of the can, and put it into the can, put on the top, then cover the whole thing in black photographic masking tape to keep out the light.  Of course, doing the film handling would have to be done in a totally dark "darkroom", without even the typical red light.  Actual camera shops that have darkrooms are rare, but I think I found one in ABQ.  Maybe someone that works there would be willing to help us get the film in, out and process it.  The packaging would also have to be sturdy enough to withstand the rigors of flight.  Does anyone have any better idea?

      Question for you physicists out there: Do we ned to use ASA 3200 film, or is ASA 100 or 400 fast enough?  At what point can you do the work with a red-light darkroom where you can see something?

      I had another thought.  What about contacting my local dentist office and getting a dozen Bitewing tabs?  Do you think that the frequency response and sensitivity of this film is sufficient to capture X-Rays and Gamma Rays on a HAB run?  The packaging would be much simpler.  From an elementary school science perspective, you could build up a foam strip with cut-outs for the bitewing tabs, maybe 6 per payload.  2 would be unshielded.  2 would be shielded with a cut up lead film bag.  2 would be shielded with aluminum foil.  If I assume that the Bitewing tabs are fast enough, I would expect to see differences in the number of "hits" on the film, depending on the shielding.

      Plan would be to fly 2 identical payloads, one on each balloon, and compare the results.


      Bill Ripley

      New Mexico Space Studies

      (505) 503-7491 (Office)

      (505) 980-8353 (Cell)



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