Even more speculation here. But hey its worth a try. Would it be possible to work this problem in a reverse per say. Meaning if your gamma radiation functions similar to light then how does one adjust light when they cannot stop down their aperture? Either use a neutral density filter or a slower film emulsion. Since I do not know what type of material you are exposing and you say that you need the thickness of lead then would it be possible to find some kind of gamma radiation neutral density filter material and then reduce the thickness of the pinhole plate? Or place this neutral density material over the exposed material and then thin out the lead pinhole plate? Just my few words. Granted they are more to ponder I suppose.
On 5/13/03 02:39 PM, "Nick Dvoracek" <dvora...@vaxa.cis.uwosh.edu> wrote: > Jenn, > > Probably in the realm of idle speculation here. > > Field of view would be dependent on focal length just like visible > light. > > Resolution is also a function of the size of the pinhole based on the > standard circle of confusion arguments, The smaller the pinhole, the > greater f is, therefore the sharper the image. > > On the lower limit, optimal pinhole size is a function of the > wavelength and focal length. Since the wavelength of gamma rays is so > short, it would be pretty hard to get a hole small enough for this to > come in to play. > > The thick piece of lead is going to be your biggest problem. The ideal > pinhole is in a planar surface. In actual practice, this means as > thin a material as is opaque to the radiation involved. I 'm afraid I > don't know the arguments, but when the hole becomes a tunnel, image > quality fails, first because it restricts the field of view (strictly a > geometry thing again) , and secondly because of internal reflections > inside the tunnel (but I don't think gamma rays will reflect normally > off a lead surface). There's gotta be some other reason also, the > Victorian authors I've read make a big deal about the thinness of the > material. > > Some of the first high energy astronomy detectors were clusters of > tunnels like this that didn't form an image exactly, just restricted > the field of view so much that they detected that there was a source of > light somewhere in the direction the tunnel was pointing. > > Interesting idea though. > > On Tuesday, May 13, 2003, at 12:01 PM, jennem...@mad.scientist.com > wrote: > >> Hello, >> >> I'm working on a project that I thought might interest people here and >> I could certainly use input from people with more experience than I. >> >> I am working as a Medical Physicist for my summer Co-op position. One >> of the projects I am working on is an attempt to use a x-ray >> flouroscopy screen and a thick piece of lead with a hole drilled >> through the center to try and image the position of a point source of >> radiation in a radiation therapy procedure. The radiation used is >> gamma-radiation which is an electromagnetic wave like light so it has >> most of the same properties. >> >> I am trying to optimize the Field of View and the Resolution and can't >> find _any_ resources for pinhole imaging with the pinhole in a thick >> material. (The thickness is required, otherwise the strength of the >> radiation will over-expose the screen and all we will see is white.) >> Any knowledge, links or even idle speculation would be appreciated. >> >> Thanks, >> Jenn >> ______________________________________________ >> Quantum Mechanics: The dream stuff is made of >> >> -- >> __________________________________________________________ >> Sign-up for your own FREE Personalized E-mail at Mail.com >> http://www.mail.com/?sr=signup >> >> >> _______________________________________________ >> Post to the list as PLAIN TEXT only - no HTML >> Pinhole-Discussion mailing list >> Pinhole-Discussion@p at ??????? >> unsubscribe or change your account at >> http://www.???????/discussion/ >> >> > ---------------------------------------------------------------------- > Nick Dvoracek dvora...@uwosh.edu > Director of Media Services Voice: 920-424-7363 > University of Wisconsin Oshkosh Fax: 920-424-7324 > http://idea.uwosh.edu/media_services/home.html > http://idea.uwosh.edu/nick/handouts.htm > > > _______________________________________________ > Post to the list as PLAIN TEXT only - no HTML > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.???????/discussion/
