Different spectral sensitivities

[davidwrogers]

Do they make films or digital backs sensitive to gamma rays or microwaves or what have you? Just wondering. I'm aware that you would require special lenses and probably some sort of barrier around the film. But the idea popped up and I figured someone here might know.

[Preston]

If there were enough gamma or microwaves to create an image for earth-bound observers, I don't think I'd want to be in the general neighborhood. :-)

http://imagine.gsfc.nasa.gov/docs/sc...detectors.html

http://missionscience.nasa.gov/ems/06_microwaves.html

--P

[ic-racer]

Yes, most film is sensitive to gamma rays. Usually the images made with this technique are photograms, so no lens is needed. Of course these rays are dangerous, so its not much of a hobby thing.

[Nathan Potter]

Well what can I say? Gamma radiation is a long way from microwave radiation when it comes to wavelength and energy. Somewhere in between is light that we can see and refract using glass lenses. We can even use glass into the ultraviolet and near infrared that we can't see but we can't go much beyond either side and get an adequate focus using glass.

Physics tells us that as radiation wavelength gets shorter the energy of a photon of that wavelength gets higher. There is dam little energy in a microwave photon (huh) but a very high energy in an xray or gamma photon.

Film was designed for visible light using silver halide emulsions where an optical photon has enough energy to cause an atomic transition in the halide emulsion. Since shorter wavelength xrays and even shorter gamma radiation has a lot higher energy there is little problem in exposing film. Going in the other direction to longer wavelengths from the visible to infrared to say Terahertz microwaves to normal microwave radiation each photon has progressively less energy which is progressively more insufficient to cause an atomic transition.

This has all been a real dilemma for scientists over the past few centuries but gradually the fog has lifted and the nature of radiation has been revealed quantitatively through classical electrodynamics.

Lenses for use with xrays and shorter radiation are almost nonexistent so these sources are configured as point sources for imaging purposes. Both film and digital backs can be configured as recording mediums, especially for xrays though the technology is somewhat new. Even gamma radiation is somewhat useful due to it's penetration characteristics but I believe there is little actual imaging done yet.

When we get back to microwave radiation, photon energy is too low to cause convenient atomic transitions for use as a detector so imaging takes the form of a radar pulse, an entirely different imaging technology than with lenses.

Nate Potter, Austin TX.

[Preston]

That's a very succinct and accurate explanation, Nate.

Thanks,

--P

[Arne Croell]

Gamma rays can be focused by diffraction in a material with a graded crystal lattice constant such as germanium-silicon ("Laue lens"), it is done for astrophysics: http://www.springerlink.com/content/2245635578138772/. The basic mechanism and a few other concepts are shown here: http://www.google.de/imgres?imgurl=h...4Q9QEwCw&dur=1

Imaging gamma ray detectors can be made from semiconductors such as cadmium zink telluride. The resolutuon is not very high.

[Steve Goldstein]

Some orbital gamma-ray telescopes also using grazing-incidence reflectors. These are complex structures built to very tight tolerances. Only governments and people like Bill Gates can afford to build them...

[Jim Michael]

Also check out zone plates.

[Chilidog]

Lenses for use with xrays and shorter radiation are almost nonexistent so these sources are configured as point sources for imaging purposes.

I suppose one could make a simple pinhole out of lead foil. You could put a thin film of material invisible to x-rays but opaque to visible light over it (black plastic film?)

The problem is: how much ambient x-ray light is out there?

even more importantly, how much is "reflected" as opposed to simply being emmitted or absorbed.

In other words, suppose you have an x-ray source in a room. various materials in the room will absorb the x-rays to various degrees, but will any of them reflect the x-rays?

[Drew Bedo]

Gamma rays are used in Nuclear Medicine. A patient is injected with an isotope that has been combined with a compound that the body processes as part of normal metabolism. The gamma rays leave the body and are captured by a special detector. There follows a lot of computer processing. In 'The Old Days" the output was a CRT display to an oscilloscope camera with8x10 film. Currently, the output is all digital and hard copy output is rare. The same is true for X-Ray (which are identical to gamma rays to a physicist). Old Days—film; today digital. X-Ray and Nuc-Med imaging use l masks and collimators made from lead in place of glass lenses.

MRI uses strong magnetic fields and radio waves to image the body. This has always been totally computer centered.

Digital sensors for DSLRs are capable of detecting infra-res end of the spectrum. The Leica M-8 uses filters on the lenses to cut the IR while most DSLRs use a filter over the sensor itself.

Any of this help at all?