On this day in science history: the first X-rays were observed
In 1895, Wilhelm Röntgen first observed X-rays during an experiment at Würzburg University. After further investigation, on 1 Jan 1896, he notified other scientists of his discovery of this new radiation that would become known as X-rays. He sent copies of his manuscript and some of his X-ray photographs to several renowned physicists and friends, including Lord Kelvin in Glasgow and in Paris. On 5 Jan 1896, Die Presse published the news in a front-page article which described his investigations and suggested new methods of medical diagnoses might be made with this new kind of radiation.
Röntgen, by Nobel foundation [Public domain or Public domain], via Wikimedia Commons
So, what are the properties of X-Rays?
X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a short period of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in cancer treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy.
Hard X-rays can traverse relatively thick objects without being much absorbed or scattered. For this reason, X-rays are widely used to image the inside of visually opaque objects. The most often seen applications are in medical radiography and airport security scanners, but similar techniques are also important in industry (e.g. industrial radiography and industrial CT scanning) and research (e.g. small animal CT). The penetration depth varies with several orders of magnitude over the X-ray spectrum. This allows the photon energy to be adjusted for the application so as to give sufficient transmission through the object and at the same time good contrast in the image.
X-rays have much shorter wavelength than visible light, which makes it possible to probe structures much smaller than what can be seen using a normal microscope. This can be used in X-ray microscopy to acquire high resolution images, but also in X-ray crystallography to determine the positions of atoms in crystals.
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