x ray photography

[monica]

Hello everyone. My name is Monica and I’m in my final year of photography at the University of Huddersfield, and for the major project I would like to do some x- ray photography using 5x4 films. The "big" problem is how to measure and how long the exposure should be. Can anyone help me with this? Thanks a lot. Monica.

[Ernest Purdum]

I can't help directly, but I think Kodak can. I'm fairly sure I remember x-ray technique being the subject of one of their pamphlets.



It's an interesting subject. I remember a technician at Lockheed Aircraft Corporation. His days were spent taking x-rays of welded assemblies and other prosaic subjects, but the walls of his office were decorated with beautiful x-ray images of flowers, watch mechanisms and other subjects I can't remember now.



The Chambered Nautilus is an example of one of the most beautiful shapes in nature, with the full beauty hidden inside.

[James E Galvin]

The exposure is easily calculated IF you know the X-ray tube output and the film sensitivity to X-rays. You also need the distance of the film from the tube and the transmission of your suject. Or you could use an X-ray "lightmeter". But you probably don't have those numbers. Also note that as you change the energy (the X-ray tube voltage), the transmission of your subject and probably the sensitivity of the film changes. So the only way is trial and error. Try 1 second. This is were Polaroid is good, you don't have to wait. If no picture, try longer (or shorter), maybe by a factor of several (even 10) till you find the ballpark. Well before the end of a box of 20, you should have it. I did an X-ray Polaroid several years ago and got it the third try (lucky), 3 minutes with a weak X-ray source. As I mentioned on the other forum, Polaroid type 55 also gives you a negative. 4x5 Polaroid is available in several speeds. Its about $2 a shot.

[monica]

Thanks a lot for being so quick with your answers.

[Al Miller]

This post is about a different kind of x-ray imaging. Most of the time when you think of x-ray pictures what comes to mind is the medical or industrial imaging kind, where the radiation passes through an object and you photograph the resulting shadow. But you can also do reflected-light x-ray photography!

I did a Ph.D. in physics where we did studies of radiation damage in SiO2 glass using x-rays from standard x-ray tube sources. We mostly used tungsten and copper tubes in an apparatus originally build for crystallography. There were a few times when I found it handy to build an x-ray pinhole camera, and it was very simple and effective. The camera was simply a lead-lined box with a pinhole on one side, and a board where we taped regular RC b&w printing paper on the opposite side. Over the pinhole was taped a piece of black plastic cut from the envelope that the photographic paper comes in. The entire experimental apparatus was enclosed in a lead radiation enclosure. The dimentions of the pinhole camera were about 10cm on a side, perhaps slightly larger.

I've forgotten many of the details (this was 15 years ago, and my lab books are packed away) but I do remember that exposure times were reasonable (30 seconds or so). I probably used Kodak Polycontrast RC paper or similar. B&W negative film should work well, and I'm guessing would be more sensitive than printing paper.

Using this setup I was able to photograph the image of the electron beam as it struck the anode, and also "see" how the radiation was scattered around the apparatus. We needed to know this to calculate the dose applied to various parts of our samples and detectors, and to locate sources of scattered radiation. And also because it was fun!

Have fun but be careful!

Al

[JohnnyV]

Go to Steve Meyers' site and contact him:

http://www.xray-art.com/

Steve might be able to give you a few pointers.

[Emmanuel BIGLER]

Monica.

The range of X-ray wavelengths is large ; in terms of wavelengths from 1 nm to 0.01 nm or in terms of photon energy from about 1 kEv to 100 keV. The conversion formula is : energy (kEv) = 1.24/lambda (nanometers). So X rays cover at least two orders of magnitude in energy ; compare to visible light that covers only a narrow range from 400 to 800 nm. In fact the sensitivity depends on the range of wavelengths you'll work with. The choice of wavelength depends on how thick your objects are and what kind of atomic elements are contained inside. I did a Ph.D. where I made contact prints of tiny rock samples @ 0.15 nm X-ray wavelength, (copper wavelength). Most probably you'll experiment with medical X rays at a higher energy ("tungsten" anode) with a much better penetration depth.

In any case you should be extremely careful when using X rays. The safiest is when the object and source are both enclosed behind some kind of metallic chamber, so that you can't switch the X rays on as long
as the chamber is not perfectly locked. X ray films are contained in a light tight film holder very similar to photographic film holders except that you do not need to remove the dark slide before exposure to X rays if the dark slide is made of plastic ;-);-) Black carbon-loaded plastic like the one used to contain photographic paper is excellent : extremely dark for visible light, almost transparent to medical X rays.

As far as contrast is concerned, organic or plastic materials deliver a very weak contrast with medical X rays. Best contrast is obtained with various metallic or glass materials embedded in something with a smaller absorption coefficient. This coefficient changes dramatically from the 0.1 nm range (crystallographic X rays) to the 0.01 nm range (Xrays for medical and non destructive testing applications) and changes also greatly from light materials like carbon (=wood, plastics), aluminium to "heavy" materials like brass, steel and lead.

As a rule X ray aborption is insentitive to
chemical bonds, mostly atomic elements determine X-ray absorption and image contrast. So in fact it depends on which X ray tube you'll have access to. Each tube delivers a certain X ray wavelength, X ray film manufacturers will give you the typical exposure data according to the kind of tube you use.

[Dan Smith]

Maybe you can make still life setups & put them into suitcases, back them with a sheet of Xray film & send them through the Airport Xray machines? Might finally get something useful from our wasted Tax Dollars.

[Alan Rockwood]

Can you use X-ray film for ordinary (light, not X-ray) photography?

[Emmanuel BIGLER]

Can you use X-ray film for ordinary (light, not X-ray) photography?

Yes. It is a silver halide film like any other, except for a thick layer, but the film is blue-sensitive only.

Most modern X-ray film is in fact a stack made of a luminescent screen converting X rays to visible plus a silver halide visible-light sensitive layer. This combination has a better detection efficiency than a single silver halide layer exposed directly to X rays, therefore, the required doses are smaller.