Crossposted at Politicook.net.
The end of the 19th Century and the beginning of the 20th were heady times in physics. Within a month of Wilhelm Konrad von Roentgen's publication of the discovery of X-rays, Henri Becquerel announced the discovery of natural radiation from uranium ore. Things were beginning to move quickly.
X-rays are generally agreed to have wavelengths from 10 nanometers to 10 picometers, making them the next region higher in energy with respect to UV. Roentgen accidentally discovered X-rays while performing experiments with a "Crookes Tube", an evacuated glass tube in which two electrodes are sealed and a high voltage direct current applied.
These tubes were used to study electrical discharge, and it was known that some ray existed inside of the tube while energized that caused the glass to glow a ghostly bluish green. It was also known that these rays did not penetrate either the glass tube nor objects placed inside the tube made of materials as flimsy as paper to try to block them, and that their path could be deflected by a magnet. We now know that these rays were electrons, being accelerated from the negative electrode towards the positive one. Interestingly, that exact principle has been used in television from its advent until just now, when LCD and plasma displays are supplanting it. In Crooke's day, these streams of electrons were referred to as "cathode rays", and sure enough, we still call a television tube a CRT, or cathode ray tube. By the way, early color television tubes emitted quite of bit of X-ray energy, which is why CRT envelopes now contain a significant amount of lead to absorb them.
Roentgen was experimenting with a particularly powerful Crookes tube one evening in his laboratory and happened to look across the room at a screen that he had been using for another experiment. This screen had the be the property of being phosphorescent, in that short wavelengths are converted into longer ones, ones in the visible. His screen was glowing brightly, but his other experiment was not active at the time. Something in his Crookes tube was penetrating the glass and causing the screen to glow. Since he had enclosed his tube in black heavy paper except for the little port into which he looked, something had to be new.
Here is a video of a couple of Crookes tubes in operation:
http://www.youtube.com/...
After fooling around with his souped up tube for a while, Roentgen decided to try an experiment. Enlisting the assistance of Mrs. Roentgen, he had her hold her hand against a photographic plate that was covered in black wrappings, and to allow him to expose the plate with the hand in front, to the rays coming from the tube. Here is the result, the first known X-ray photograph of a human body part:
http://i298.photobucket.com/...
Note the "nodule" on the ring finger. It is, in fact, Anna von Roentgen's wedding ring. Pretty cool for something over 110 years old.
X-rays, like all electromagnetic radiation, can be produced from blackbody radiators if the temperature is great enough, and in stars it is. Not many solid substances can withstand the temperatures that "hard" X-rays demand for blackbody generation, but the plasmas in stars easily fill the bill. The other main way for generation of X-rays is to promote inner shell electrons to very high energies, and when other electrons "fall" back into the low energy, unoccupied level, X-rays are produced. That is how the Crookes tube worked, and is how medical and research X-rays are produced now. Instead of just having two small electrodes, modern X-ray generators have a "hot" cathode (one that not only is at a high voltage potential, but also literally heated by a direct current running through it. For us geezers who have seen conventional vacuum tubes work, the dull red glow is the hot cathode). The electrons are focused magnetically onto a target, usually a tungsten (wolfram) anode at an angle that directs the X-rays produced towards the intended object.
X-rays have a myriad of uses. Certainly, the medical use of them has revolutionized imaging, and still are cost effective and extremely useful for many purposes. Higher resolution techniques, such as MRI, positron emission tomography (PET, which actually uses the gamma), and computer assisted tomography (CAT) are replacing X-rays for sophisticated purposes, but X-rays are fast and cheap and good enough for many purposes. Advances in film technology has reduced the radiation exposure for most routine diagnostic X-rays to not much different than one gets in a coast-to-coast plane trip. The old, slow film from years ago required much higher exposure levels. I shudder to think how much exposure that Mrs. Roentgen received in the picture, since the best photographic plates were around ASA 1 to 2 at the time.
Other uses of X-rays include determination of atomic structure of solid materials. Because crystals are composed of repeating patterns, with atomic spacings in the ~100 picometer, give or take, range, X-rays are well suited to examine these materials. The father and son team of Bragg and Bragg developed this technique to a high degree of accuracy, and it is appropriate to mention them this Father's Day.
X-ray fluorescence, XRF, is a common tool for quantitative analysis of elements in complex compounds, and is nondestructive and very fast. In essence, you hit the sample with a relatively intense burst of X-rays and see what wavelengths come back. Some instruments are not much larger than a laptop computer.
Industrial uses are myriad, from detection of flaws in fabricated parts from production lines to sterilization of food, although gamma is also used for both of these.
There are so many uses for X-rays that it easily could takes hundreds of small type pages just to list them, so I will not try. I just hit some of the historical high points and some of the most common industrial and research uses. I will, however, debunk Superman's X-ray vision, talk about shoes, and then wrap up with dangers of X-rays. I would be extremely interested in any comments and personal experience that readers have using X-rays.
With my apologies to Clark Kent, he just could not see the way that the comics show. Vision is necessarily a phenomenon wherein EMR is reflected from an object, or emitted from an object, to the eye. I make the assumption that Kryptonian eyes are similar in gross structure and function to human ones. Emitting X-rays to penetrate a wall, for instance, offers no assistance in seeing what is behind it UNLESS the object behind the wall reflects those X-rays AND those X-rays penetrate back through the wall and are focused by his lens into an image, assuming that his eyes are transparent to X-rays AND his retina sensitive to them. Except for X-ray diffraction where they are reflected is a very controlled manner, all X-ray images are formed just like Mrs. Roentgen's: the rays penetrate the object and are observed on a film, screen, or other sensitive detection device BEHIND the source and the object. I will temper this by saying that the new airport technology that allows the TSA to see under our clothes does involve backscatter reflection, and would solicit input from readers to explain this more thoroughly.
When my Mum was a slip of a girl (she was born in 1921, rest her soul), one could go to the shoe store and get fitted for shoes by inserting one's feet into a very powerful, from the standpoint of radiation exposure, fluoroscope. You could flex your toes and watch your bones, and there were viewing ports for the shoe salesman and Mum and Dad. This went on for some time, and exposed lots of people to intense irradiation on their feet, which were the targets, but also whole body exposure because the shielding was, to be kind, extremely deficient. I have looked and can not find a picture of one of those units, and would appreciate it if anyone has one to post. If so, I will try to incorporate it as an update. I suspect that a few of these may be knocking around in antique stores to this day.
The dangers of X-rays are similar to those of UVB and UVC, but more pronounced. X-rays easily ionize any matter on which they impinge, and by stripping electrons from DNA, cause even potentially more damage that I described in the UV installment. They also degrade proteins, destroy vitamins, and cause other damage that has to do with the destruction of normal chemical bonds in living systems. In addition, the energetic byproducts of this damage can also cause even more damage to cells that were not directly affected by the X-rays themselves.
This is one of the reasons that X-rays are used to combat skin cancer. It turns out that cancer cells, in many cases, are more sensitive to ionizing radiation than "normal" ones. The reason is essentially similar to what I reported about UV last time: all cells are affected more of less the same, and we have repair mechanisms for some of that damage, or killer mechanisms to destroy cells too far gone to repair. However, cancer cells tend to divide, in general, much more rapidly than normal cells, so the probability is greater that cells with a fatal flaw will reproduce before repair is greater for cancer cells than for normal cells. It is matter of probability: you will damage all cells to some extent, but the normal ones have more time to undo the damage than the cancerous ones have. Thus, the introduction of ultimately deadly changes in cells is higher in cancer cells than in normal ones. This is just a very general idea, but seems to work in many cases. We still are not positive about what we are doing.
I wanted to embed the video and picture in the body of this piece, but could only link to them. Since the FAQ part of the site is down, I did the best that I could under the circumstances.
Update: A commenter asked for links to previous installments. I will attempt to post them here, but if not legible, just go to my profile and click "Diaries".
No luck. Try backtracking on my profile, and I will try to learn how to link them for the final installment.
Warmest regards, Doc.
Update: I am very pleased to say that 58% of the responders knew what the Chandra effort is. My polls are usually serious to a measure, and with at least one or two humorous alternatives. I always vote the "pie" choice for sport. But way over half of you indicated that Chandra was important, and I could not agree more. What a wonderful bunch of folks inhabit this realm. Warmest regards, Doc.