A short history of x-rays

by Arne Hessenbruch

• Abstract
• The new radiation: what is it good for?
• The medical market
• X-ray diffraction: a tool for probing the atomic scale
• Protection: an infrastructure
• The marriage of the computer with the x-ray
• Controlling and quantifying: Sources and detectors

The new radiation: what is it good for? (1896-1920s)

X-rays were discovered in late 1895 by Wilhelm Conrad Röntgen, a Professor of Physics at the University of Würzburg, Germany [1] . The ability of the new rays to image the bones within a living hand interested the general public for some six months. Theatres produced humorous X-ray plays, many jokes circulated in newspapers, and advertisements promising x-ray proof underwear emerged. It has been suggested that during this x-ray craze the general public genuinely feared the loss of privacy and that the x-rays marked a serious departure for the public perception of science - the first instance of the scientist as the wizard's apprentice losing control [2] . But a closer examination of the sources reveals that the media merely expected their readers to be titillated by the idea of nudity in public, everyone knowing full well that no prying x-ray eyes would undermine privacy. The jokes mostly played on the patently absurd, such as the tax authorities examining hidden treasures or the highway robber handily exploiting x-rays to determine which pockets to empty [3] .

Interest persisted in the use of x-rays for diagnostic purposes and for physical research. Interest was also sustained for a few years within a community of spiritualists who interpreted the x-rays as indicative of another world inaccessible to the senses of all but a few particularly sensitive individuals. X-rays not only connoted morbidity by virtue of the images of human bones and skeleta but also revealed the unseen, the association being with unseen spirits. Most mainstream scientists simply ignored such interpretations, but a few well-known scientists, such as William Crookes and Friedrich Zöllner, participated in séances measuring the spiritualist mediums with various scientific instruments. The attitude gradually won through that these mediums were simply skilled illusionists and that laboratory expertise did not equip one to detect sleight of hand so that the task of checking spiritualist séances should rather be left to stage magicians. In fact, in the late nineteenth century, stage magicians generally abandoned the wizard's cloak and began instead to don the tuxedo, emphasizing their professionalism, utilizing science to produce illusions. Several publicly denounced the mediums and publicised how to perform the tricks. They saw themselves as serving humanity in the role of handmaidens of the Enlightenment and as scientific illusionists and thus as superior to mediums or non-Western magicians, such as fakirs [4] .

In the period until World War I, the field of diagnostic radiography matured. The practice of diagnostic radiography worked well with a conception of x-rays as similar to visible light possessing wavelength and intensity. Shorter and thus more energetic wavelengths were less well absorbed by bone than longer, less energetic ones. The contrast desired of an x-ray photograph could be achieved by manipulating the x-ray tube producing more of one kind of x-rays and less of another. Physicists worried over the nature of x-rays in this early period because the phenomena well-known to light (diffraction, refraction, and interference) were not observed for x-rays. In fact, a concept of x-rays as bunched up radiation, almost particle-like, persisted amongst some physicists, and Bruce Wheaton has argued that the dualistic concept of radiation as both a particle and a wave - so important for quantum mechanics in the 1920s - has its origin in the persistence of both theories of x-rays [5] . Maybe Wheaton is right, but almost everybody just considered x-rays another form of electromagnetic waves because of the experience with routine radiography.