page_title: Paul Ulrich Villard
section_title: Later work
hierarchical_section_title: Paul Ulrich Villard / Later work
caption_attribution_description: English: Photo of experimenters taking an X-ray with an early Crookes tube apparatus, from the late 1800s. The Crookes x-ray tube is visible suspended at center. The upper man is examining the bones of his hand with a fluoroscope screen. The lower man is taking a radiograph of his hand with a photographic plate. The power source is an induction coil, seen at left, and the mechanism immediately to its right against the wall is a motor-operated 'break wheel' interrupter in the coil's primary circuit. The large flat disk on the table is a rheostat (adjustable resistor) power control to adjust the primary current to the coil. Several spare Crookes X-ray tubes are seen in a rack on the wall. The apparatus is described and diagrammed on p.88 of the source. No precautions against radiation exposure are taken; its hazards were not known at the time. The original image was half-tone. Alterations: removed frame.
context_page_description: Paul Ulrich Villard was a French chemist and physicist. He discovered gamma rays in 1900 while studying the radiation emanating from radium.
context_section_description: Villard spent much time perfecting safer and more accurate methods of radiation dosimetry, which had been done very crudely up until then (typically by evaluating the quality of the image of the experimenter's hand produced on a photographic plate). In 1908, Villard pioneered the use of an ionization chamber for the dosimetry of ionizing radiation. He defined a unit of kerma which was later renamed the roentgen.
caption: Taking an X-ray image with early Crookes tube apparatus in 1896. The Crookes tube is visible in the centre. The standing man is viewing his hand with a fluoroscope screen. This was a shortcut method for setting up the tube.No precautions against radiation exposure are being taken.
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