160. Uncle Tungsten - XIII. Penetrating rays

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Uncle Tungsten

I'm a little out of order if you've been reading my latest posts after failing -- not sure how -- to post 158 the other day. Make sure you've read "159. Cold fire" before continuing here.

Chapter 19 - Ma

A nice chapter mostly about his mother, but nothing of particular interest relating to science. 


Chapter 20 - Penetrating Rays

p244 It was in Abe’s attic that I was introduced to cathode rays. He had a highly efficient vacuum pump, and an induction coil -- a two-foot-long cylinder wound with miles and miles of densely coiled copper wire and set on a mahogany base. There were two large movable brass electrodes above the coil, and when the coil was switched on, there would leap between them a formidable spark, a miniature lightning bolt, something out of Frankenstein’s Lab. Uncle showed me how he could separate the electrodes until they were too far apart to spark and then connect them to a yard-long vacuum tube. As he reduced the pressure in the electrified tube, a series of extraordinary phenomena appeared inside it: first a flickering light with red streamers like a miniature Aurora Borealis, then a brilliant column of light filling the whole tube. As the pressure was lowered still further, the column broke into discs of light separated by dark spaces. Finally, at a ten-thousandth of an atmosphere, everything became dark again inside the tube, but the end of the tube itself started to glow with a brilliant fluorescence. The tube was now filled, Uncle said, with cathode rays, little particles shot off the cathode with a tenth the speed of light, and so energetic that if one converged them with a saucer-shaped cathode they could heat a piece of platinum foil to red heat...

p245 Cathode rays, Uncle Abe assured me, could travel only two or three inches in ordinary air -- but there was another sort of ray, far more penetrating, which Wilhelm Roentgen had discovered in 1895 while experimenting with just such a cathode-ray tube. Roentgen had covered the tube with a cylinder of black cardboard to prevent any leakage of cathode rays, and yet he was astounded to observe that a screen painted with a fluorescent substance lit up brilliantly with each discharge of the tube, even though it was halfway across the room.

...For the next six weeks he investigated the properties of these extraordinarily penetrating new rays and found that, unlike visible light, they could not, apparently, be refracted or diffracted. [This doesn't seem to be true.] He tested their ability to pass through all sorts of solids and found they could pass to some degree through most common materials and still activate a fluorescent screen. When Roentgen placed his own hand in front of the fluorescing screen, he was astonished to see a ghostly silhouette of its bones... in his first paper he was able to publish photographs taken by the X-rays, as he called them -- including a radiograph of his wife’s hand, her wedding ring encircling a skeletal finger.

p246 On January 1, 1896, Roentgen published his findings and first radiographs in a small academic journal, Within days the major newspapers of the world picked up the story. The sensational impact of his discovery horrified the shy Roentgen, and after his initial paper and a verbal presentation the same month, he never discussed X-rays again, but returned to working quietly on the varied scientific interests which had engrossed him in the years before 1896. (Even when he was awarded the first Nobel Prize in physics in 1901 for his discovery of X-rays, he declined to give a Nobel speech.)

...By the end of 1896, more than a thousand scientific articles on X-rays had appeared. The response to Roentgen’s rays, indeed, was not only medical and scientific, but seized the public imagination in various ways... A ditty appeared in the journal Photography, ending,

I hear they’ll gaze
through cloak and gown -- and even stays,
those naughty, naughty, Roentgen rays. 

My uncle Yitzchak, after being in practice with my father during the months of the great flu epidemic, had been drawn into the practice of radiology soon after the First World War. He had gone on, my father told me, to gain uncanny powers of diagnosis by X-ray, able almost unconsciously to pick up the smallest hints of any pathological process.

In his consulting rooms... Uncle Yitzchak showed me something of his apparatus and its uses...

Is that really the best way to phrase that? 

p249 Like Uncle Dave, Uncle Yitzchak retained a strong interest in the theoretical foundation of his subject and its historical development, and he also had a little “museum,” in this case of old X-ray and cathode-ray tubes, going back to the fragile, three-pronged ones that had been used in the 1890s...

It was... apparent from the start that X-rays carried a good deal of energy and would generate heat wherever they were absorbed. Yet, penetrating as they were, X-rays did not have too great a range in air. It was the opposite with wireless waves, radio waves, which, if properly projected, could leap across the Channel with the speed of light. These, too, carried energy...

p250 While X-rays took off, engendering innumerable practical applications... they elicited a very different train of thought in the mind of Henri Becquerel. Becquerel was already distinguished in many fields of optical research, and came from a family in which a passionate interest in luminescence had been central for sixty years. (Footnote: Henri Becquerel’s grandfather, Antoine Edmond Becquerel, [Sacks seems to have in mind here Antoine César Becquerel] had launched the systematic study of phosphorescence in the 1830s and published the first pictures of phosphorescent spectra. Antoine’s son, Alexandre-Edmond, had assisted in his father’s research and invented a “phosphoroscope,” which allowed him to measure fluorescence that lasted as briefly as a thousandth of a second. His 1867 book, Lumiere, was the first comprehensive treatment of phosphorescence and fluorescence to appear (and the only one for the next fifty years).) He [Henri] was intrigued when he heard in early 1896 the first news of Roentgen’s X-rays and the fact that they seemed to be emanating not from the cathode itself but from the fluorescent spot where the cathode rays hit the end of the vacuum tube. He wondered whether the invisible X-rays might not be a special form of energy that went along with the visible phosphorescence -- and whether indeed all phosphorescence might be accompanied by the emission of X-rays. 

That occurred to me as well. 

p250 Since no substance fluoresced more brilliantly than uranium salts, Becquerel pulled out a specimen of a uranium salt, potassium uranyl sulfate, exposed it to the sun for several hours, and then laid in on a photographic plate wrapped in black paper. He was greatly excited to find that the plate was darkened by the uranium salt, even through the paper, just as with X-rays, and that a “radiograph” of a coin could be easily obtained.

Becquerel finally discovers that exposure to the sun -- and fluorescence -- has nothing to do with what was happening. 


p251 Becquerel had discovered a new and much more mysterious power than Roentgen’s rays -- the power of uranic salt to emit a penetrating radiation that could fog a photographic plate, and in a way that had nothing to do with exposure to light or X-rays or, seemingly, any other external source of energy. [It just occurred to me that this would have been an easier way for Primo Levi, in The Periodic Table, to have tested what he was told was uranium.] Becquerel, his son later wrote, was “stupefied” at this finding... as Roentgen had been by his X-rays -- but then, like Roentgen, he investigated the “impossible.” He found that the rays retained all their potency even if the uranic salt was kept for two months in a drawer; and that they had the power not only to darken photographic plates but also to ionize air, render it conducting, so that electrically charged bodies in their vicinity would lose their charge. This indeed provided a very sensitive way of measuring the intensity of Becquerel’s rays, using an electroscope. 

Wouldn’t there also be a detectable amount of helium generated by the uranic salt? Or not? 

Investigating other substances, he found that this power was possessed not only by uranic salts but uranous ones too, even though these were not phosphorescent or fluorescent. On the other hand, barium sulfide... and certain other fluorescent or phosphorescent substances had no such power. Thus the “uranium rays,” as Becquerel now called them, had nothing to do with fluorescence or phosphorescence as such -- and everything to do with the element uranium. They had, like X-rays, a very considerable power of penetrating materials opaque to light, but unlike X-rays, they were apparently emitted spontaneously. What were they? And how could uranium continue to radiate them, with no apparent diminution, for months at a time?
...
p252 Though uranium had been known since the 1780s, it had taken more than a century before its radioactivity was discovered... had anyone chanced to place a piece of pitchblende close to a charged Leyden jar or an electroscope... or... in accidental proximity to a photographic plate... [it could have been discovered before.] Yet had radioactivity been discovered earlier, it would have been seen simply as a curiosity, a freak... its enormous significance wholly unsuspected. Its discovery would have been premature, in the sense that there would have been no nexus of knowledge, no context, to give it meaning. Indeed, when radioactivity was finally discovered in 1896, there was very little reaction at first, for even then its significance could barely be grasped. So in contrast to Roentgen’s discovery of X-rays, which instantly captured the public’s attention, Becquerel’s discovery of uranium rays was virtually ignored.

This makes sense as far as the public is concerned as there is no obvious practical application for something that merely fogs photographic plates. Maybe you could take a very slow medical “X-ray” using uranium, but then you would lose the electrical drama of the early X-ray machines. But why would scientists not jump all over this? Were they overwhelmed by the somewhat less confusing X-ray discovery? Was it simply too strange to comprehend? Like the Spanish sailing ships that showed up off the coast of the Americas that were so unprecedented that natives could hardly even see them? 


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