Although the paper contained no illustrations, a reprint with the x-ray of Roentgen’s wife’s hand was sent to a colleague in Berlin, who presented it as a poster at the Berlin Physical Society meeting on January 4, 1896. It was the first public viewing of an x-ray image.39
Another set of reprints and x-ray images was sent to colleagues in Vienna, one of whom happened to be the son of the editor of Vienna’s newspaper Neue Freie Presse. The son showed the material to his father, who rushed the story into the January 5 issue, along with the x-ray image and a discussion of the potential medical utility of the discovery.40 The next day, the Chronicle in London picked up the story. Although the more prestigious Times of London initially passed on publishing—assuming the finding to be some sort of minor photographic advancement—even they had to eventually publish Roentgen’s discovery (albeit after being scooped by many other news organizations). From Europe, the story spread like wildfire throughout the world. It was published in the New York Sun on January 6, and the New York Times on January 12.41 So both the scientific community and the general public became enamored with x-rays and their potential at virtually the same time, and Roentgen became an overnight celebrity. Not until 50 years later, when President Harry S. Truman (1884–1972) announced the creation of the atomic bomb, would a scientific event of any kind receive as much media attention as the discovery of x-rays.42
The coupling of the discovery with a practical medical use likely contributed to the enormous fame that Roentgen immediately enjoyed, but that had eluded Hertz and his radio wave discovery just a few years before. The journal article on x-rays also had the distinction of being one of the few physics papers that contained no mathematical calculations, so the work could be easily understood by nonscientists, including the news media and much of the public.
Seeing is believing, and Roentgen’s x-ray photographs were evidence that was hard to refute. Most people regarded them as proof of the discovery. Besides, Crookes tubes were widely available to scientists and engineers throughout the world, so any scientist who doubted Roentgen’s claims could get his own Crookes tube and replicate Roentgen’s experiments to his satisfaction. And replicate they did. Within a few short weeks, Roentgen’s results were replicated at Harvard (January 31), Dartmouth (February 3), and Princeton (February 6) universities.43 By mid-February 1896, no credible scientist in the world doubted the soundness of Roentgen’s work. His worries had been for nothing.
At McGill University, in Montreal, Professor John Cox, the Director of the Macdonald Physics Laboratory, was also fascinated by Roentgen’s discovery and had replicated the x-ray photographic imaging on February 3. Hearing of this, Robert C. Kirkpatrick (1863–1897), the doctor treating the unfortunate Mr. Cunning for his gunshot wound, prevailed upon Cox to produce an x-ray image of Cunning’s injured leg. The obliging professor took a 45-minute exposure of the leg with his Crookes tube. Even with such a long exposure time, the image of the leg was still somewhat underexposed. Nevertheless, on February 7, 1896, the bullet was found lodged against the tibia bone, and the surgeons quickly removed it. A report of the successful operation appeared in the Montreal Daily Witness the next day, which was barely six weeks after Roentgen had made his momentous discovery.44 Never before or since has any scientific discovery moved from bench to patient bedside so quickly.45
Within months of his important discovery, Roentgen became internationally acclaimed, and was awarded the Nobel Prize in Physics in 1901, which was the first Nobel in physics ever awarded. Later, he would be further honored by having a unit of radiation exposure named after him, as well as a newly discovered element (roentgenium; atomic number 111). Some even sought to rename x-rays roentgen rays, and his x-ray photographs roentgenographs, but the modest Roentgen resisted these changes. In fact, ever the self-effacing academic, he never patented his discovery, and he bequeathed all of his Nobel Prize money to the University of Würzburg.46 He considered himself to be a pure scientist, and the practical applications of his work to be the purview of others. Inventions and business were of no interest to him.
Even so, Roentgen did not just discover x-rays, collect his honors, and walk away. He subsequently dedicated his career to studying the properties of x-rays. In fact, famed British physicist Silvanus Phillips Thompson (1851–1916),47 a staunch admirer of Roentgen, once remarked, “Roentgen has so thoroughly explored x-rays that there remains little for others to do beyond elaborating on his work.”48 This would prove to be a gross overstatement. Many novel discoveries about x-rays were forthcoming. But for years, it was not far from the truth.
Unlike some other radiation pioneers who spent considerable time working with the rays, Roentgen always took precautions to shield himself from the beam. It is unclear why he did. Perhaps he was just a cautious man by nature,49 or maybe he took his wife’s remark about seeing her own death as some kind of premonition. In any event, he was wise to do so. X-ray exposures in those early years were typically quite high. For example, it took 15 minutes of exposure to produce the x-ray photograph of Roentgen’s wife’s hand—something that can be accomplished in 1/50th of a second today. Roentgen’s self-protection paid off. He lived many years and apparently suffered no ill effects from his work with x-rays.
Roentgen obviously had not set out to produce electromagnetic radiation from his Crookes tube. He was interested in the properties of cathode rays flying free through space. So how was it that Roentgen was able to produce x-rays from what was little more than a souped-up light bulb, and what underlying physical principle did his experiments reveal?
Cathode rays (i.e., flying electrons) could be deflected by magnetic fields, and this is the phenomenon that Roentgen had hoped to study. What he failed to appreciate was that the very high voltage would cause the flying electrons to bring along with them a tremendous amount of energy that they would necessarily impart upon the anode when they hit it. All that energy would need to go somewhere, and quickly. That surplus energy left the tube in the form of x-rays. Essentially, that’s all that Roentgen was witnessing, but let’s add a few more details.
It turns out that some of the excess energy carried by the flying electrons is simply dissipated as heat, which explains why the tubes get hot. In addition, however, another energy dispersing process occurs. As a high-speed electron passes near the electrically charged orbitals of a metal atom in the anode, it gets deflected from its straight path and then abruptly slows to a stop, like a speeding car swerving to miss a pedestrian and hitting a brick wall. When this happens, the energy of the fast-moving electron is immediately dissipated in the form of an electromagnetic wave, which Roentgen was calling an x-ray.50 Instead of the flying bricks that the crashing car produces, an electron crashing into an anode generates flying x-rays. Since Roentgen’s time, volumes have been written on the physics of x-rays, and you could spend a lifetime studying it. But we don’t have to go into all that here. This is as technical as we need to get to consider the effects of x-rays on health.
Ironically, the great William Crookes himself realized in retrospect that he, too, had witnessed an effect of x-rays years before but never had recognized it. He was constantly returning photographic plates that he stored in has laboratory back to the vendor, complaining that they were “fogged.” After he saw Roentgen’s paper, he knew why they were fogged; they had been exposed by x-rays as a consequence of his Crookes tube experiments. He also understood that he had missed the greatest scientific opportunity of his life.
Interestingly, Edison’s enterprises with electromagnetic radiation didn’t end with his light bulb. Three weeks after Roentgen’s discovery of x-rays and its effects on fluorescent screens, Edison started working on a medical invention he called the fluoroscope—a device that coupled a fluorescent screen with a Crookes tube to produce a live image of a patient’s internal structures.51 Edison demonstrated his fluoroscope at the National Electric Exposition in New York City’s Grand Central Palace Hotel, in May 1896.52 It proved to be an extremely useful medical d
evice, and is still in widespread use today. When President William McKinley was shot twice in the abdomen in Buffalo on September 5, 1901, his doctors called on Edison to send a fluoroscope, to guide them in the surgical removal of the bullets. Edison sent a fluoroscope at once, along with two technicians to operate it.53 But it was never used because the surgeons decided it was safer to leave the bullets where they lay, rather than extract them. McKinley then took a turn for the worse and died on September 14, and the technicians brought the unused fluoroscope back to Edison’s laboratory in New Jersey. Although Edison’s fluoroscope did not save McKinley’s life, another one of his devices helped dispense justice; on October 19, McKinley’s assassin, Leon Frank Czolgosz (1873–1901), was executed in the electric chair.
FIGURE 2.4. THOMAS EDISON VIEWING THE BONES IN HIS ASSISTANT CLARENCE DALLY’S HAND WITH THEIR LATEST INVENTION, THE FLUOROSCOPE. Edison’s fluoroscope was simply a Crookes tube mounted within a wooden box. The box provided a stage on which the hand or other body parts could be viewed. This was done by means of a fluorescent screen mounted within a hand-held, light-shielding viewer. The fluoroscope provided a real-time moving image of the bones to the viewer, with no need to wait for development of photographic film.
Despite Edison’s expressed concern about the dangers of AC electricity, he apparently had no such reservations about x-rays. Unlike Roentgen, he took no precautions to protect himself from what amounted to extremely high doses of x-rays produced by his experiments. Furthermore, his assistant, Clarence Madison Dally (1865–1904), eagerly and frequently volunteered to have his hands imaged with the fluoroscope. When one hand became badly burned by the beam, he would just switch to the other, allowing the burned one time to recover. Unfortunately, this unwise practice eventually caught up with him. He ultimately suffered severe hand ulcerations resulting in the loss of four fingers from his right hand and amputation of his left hand. It was soon found that cancer from his hands was spreading up his arms, so he had both his arms amputated as well. All these surgeries, however, were to no avail. The cancer had spread to his chest and he died in October 1904.54
Edison himself didn’t escape unscathed. He nearly lost his eyesight from the high x-ray exposures his eyes sustained through the viewfinder of his fluoroscope. Traumatized by the whole experience, Edison abandoned all work with x-rays. When later asked about that work, he replied, “Don’t talk to me about x-rays, I’m afraid of them!”
Not all investigators were as cavalier as Edison and Dally when working with x-rays. Soon after Roentgen’s discovery became public, two brothers-in-law and close friends, Francis H. Williams (1852–1936) and William H. Rollins (1852–1929)—a physician and a dentist, respectively—began collaborating in Boston with the goal of developing x-rays for medical diagnostics. In fact, many consider Williams and Rollins the fathers of diagnostic radiology.55 Yet, they always protected themselves from the beam, even before reports of injuries began to appear. Asked later why they did so, Williams said, “I thought that rays having such power to penetrate matter, as x-rays had, must have some effect upon the system, and therefore I protected myself.”56 Simple as that.
As early as 1898, Rollins had designed a metal box with a diaphragm aperture, like a camera shutter, to contain their Crookes tubes and thus limit their exposure to stray x-rays. Williams and Rollins promoted the use of the box, as well as other protective devices, among medical x-ray workers. Nevertheless, five years later, Rollins lamented, “Most of these precautions are neglected at the present time … partly due to attempts to ignore … the [known] effects of x-[rays].”57 In fact, some investigators were in complete denial that x-rays could do them harm, claiming that the skin burns were not associated with the Crookes tubes themselves, but rather from electricity leaking from the generators that powered them (so-called brush discharges). Their remedy was to stop worrying about Crookes tube x-rays and just replace the generator. It seems that long after the big AC/DC controversy, some people still remained focused on the hazards of electricity, to the exclusion of all else.
Still, Edison and Dally could plainly see that the x-ray beam itself was burning their exposed tissues, and they likely knew about the protective devices that Rollins and Williams had been heavily promoting since 1898. In 1901, Williams had even published a massive volume, entitled The Roentgen Rays in Medicine and Surgery: As an Aid in Diagnosis and as a Therapeutic Agent, in which he noted the dangers of x-rays and recommended specific protective measures for both patient and physician. It immediately sold out, and was republished again in 1902, and then again in 1903, with editions in other languages. Edison and Dally could not have been unaware of the potential health hazards, yet they seemed to lack Williams’s common sense. They ignored the safety precautions and paid the price with their health. Rollins and Williams, in contrast, never suffered any radiation injuries, and lived to 77 and 84, respectively.
It truly can be said that most of the radiation injuries suffered by early radiation workers were more the result of negligence than ignorance. There was ample evidence that x-rays could damage tissues, and there were ready means available to protect one’s body from x-ray exposure while working with Crookes tubes. Unfortunately, few chose to take the threat seriously.58
SIZE MATTERS: THE IMPORTANCE OF WAVELENGTH
Fluorescent screens and photographic films are sensitive to more types of electromagnetic radiation than is the human eye. It was the fluorescent screen and photographic film that provided Roentgen with the tools that Newton lacked. We now have many tools besides fluorescent screens and photographic film to detect “invisible” rays, and these tools have allowed us to learn a tremendous amount about x-rays and other types of the electromagnetic waves that we now simply call radiation. Today, scientists understand that all electromagnetic radiation travels in the form of waves at the same unchanging speed as waves of light (i.e., Einstein’s universal constant, c = the speed of light, from his famous E = mc2 equation).59 In fact, the difference between radio waves, x-rays, and visible light is simply the distances between the crests of their waves (i.e., their wavelengths). At the extremes, x-rays have very short distances between their crests—much less than the width of a human hair—while the distance between the crests of radio waves can be as long as an American football field.
These differences in wavelength drive all of the various properties of the multiple types of electromagnetic radiation and, most importantly, determine their energies. The shorter the wavelength, the greater the energy. This can be compared to ocean waves that strike the beach. When the distance between the crests of the ocean waves is short, many more waves hit the beach during any period of time than when the wave crests are farther apart. If more waves are hitting the beach, more energy is deposited on the beach during that time. Thus, shorter wavelengths deliver more energy and longer wavelengths less. This analogy of electromagnetic waves to beach waves is very crude and can even be misleading if carried to extreme. But it does provide a good mental picture of an electromagnetic wave that cannot otherwise be experienced or observed by our senses and is, therefore, innately hard to comprehend. Even though electromagnetic waves cannot be experienced directly by human senses, they can be detected with the use of technology; they are just as real as ocean waves, and just as powerful a force of nature.
This concept is so important to understanding radiation’s effects on health that it warrants repeating. Radiation often takes the form of an electromagnetic wave, and the wavelength of the radiation determines exactly what properties that radiation will have. These properties include everything from how penetrating the radiation is, to whether or not it causes cancer. So, as we move ahead, remember that even though the different types of radiation discussed above are all composed of electromagnetic waves, the physical, chemical, and biological effects of different wavelengths can be as different as apples and oranges—or rather, as different as apples and baseballs. The wavelength is the key.
FIGURE 2.5. WAVELENGTH ALONE DISTINGUIS
HES THE DIFFERENT TYPES OF ELECTROMAGNETIC RADIATION. Most types of radiation in commercial use are electromagnetic; that is, they come in the form of waves that differ only by their wavelengths. The radiation types with the shorter wavelengths (e.g., x-rays) carry more energy than the types with longer wavelengths (e.g., radio waves). Only a very narrow band of wavelengths near the middle of the electromagnetic spectrum is visible to the human eye.
To illustrate the importance of wavelength, let’s return to visible light and explore exactly why it is we can see it. The light we see falls in the middle of the spectrum of possible electromagnetic wavelengths. It has an extremely narrow range of wavelengths (just 380 to 740 nanometers), which corresponds to approximately 1/100th the width of a human hair.60 Electromagnetic radiation within these wavelengths can be seen by the human eye because there is a biological chemical in the retina of the eye, called retinal, that bends (i.e., photo-isomerizes) into a different molecular shape when exposed to radiation within this specific range of wavelengths. The nerve cells in the eye detect retinal’s bending and then send a signal to the brain through the optic nerve. The brain processes the spatial signals from the retina into a visual image. This process is what we call sight. Radiations with wavelengths that are too large or too small are not capable of bending the retinal molecule, and, consequently, we do not see them. Still, that doesn’t mean that such radiation is not there; it’s just that it’s invisible to us. The way we distinguish colors is a little more complicated, and not all animal species are able to see color. Color perception is beyond what we need to know about here, but let’s just say that when the wavelengths start to get too long to bend the retinal, we call them infrared because they are just below the visible color red. When the wavelengths are a little too short to be seen we call them ultraviolet because they are just beyond the visible color violet.61 Visible light is squeezed in between the invisible infrared and ultraviolet wavelengths.
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