Gamma Radiation

Gamma rays were discovered by the French chemist and physicist Paul Ulrich Villard in 1900, while he was studying uranium. Working in the chemistry department of the �cole Normale in rue d'Ulm, Paris with self-constructed equipment, he found that the rays were not bent by a magnetic field.

For a time, it was assumed that gamma rays were particles. The fact that they could be described as rays was demonstrated by the British Physicist William Henry Bragg in 1910, when he showed that the rays ionized gas in a way similar to X-rays.

In 1914, Ernest Rutherford and Edward Andrade showed that gamma rays were a form of electromagnetic radiation by measuring their wavelengths using crystal diffraction. The measured wavelengths were similar to those of X-rays and are very short, in the range of 10-11 m to 10-14 m. It was Paul Ulrich Villard who coined the name 'gamma rays', in keeping with Rutherford's naming of 'alpha' and 'beta' radiation; the individual natures of the different rays were unknown at that time.

Gamma-ray astronomy did not develop until it was possible to get detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope, carried into orbit on theExplorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. Perhaps the mostspectacular discovery in gamma-ray astronomy came in the late 1960s and early 1970s. Detectors on board the Vela satellite series, originally military satellites, began to record bursts of these rays, not from Earth, but from deep space.