Paul Ulrich Villard (28 September 1860 – 13 January 1934) was a French

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...

and

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

. He discovered

gamma rays A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

in 1900 while studying the radiation emanating from radium.

Early research

Villard was born in Saint-Germain-au-Mont-d'Or,

Rhône The Rhône ( , ; Occitan language, Occitan: ''Ròse''; Franco-Provençal, Arpitan: ''Rôno'') is a major river in France and Switzerland, rising in the Alps and flowing west and south through Lake Geneva and Southeastern France before dischargi ...

. He graduated from the

École Normale Supérieure École or Ecole may refer to: * an elementary school in the French educational stages normally followed by Secondary education in France, secondary education establishments (collège and lycée) * École (river), a tributary of the Seine flowing i ...

in 1881 and taught in several Lycées, ending with a Lycée in Montpellier. He would maintain a laboratory position at the Ecole Normale Supérieure until his retirement. At the time when he discovered what we now call gamma rays, Villard was working in the chemistry department of the École Normale Supérieure rue d'Ulm,

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

. Villard is also credited with the discovery of argon hydrate. He spent the early part of his career (1888–1896) focusing on similar compounds at high pressure.

Discovery of gamma rays

Villard investigated the radiation emitted by radium salts via a narrow aperture in a shielded container onto a photographic plate, through a thin layer of

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

that was known to stop alpha rays. He was able to show that the remaining radiation consisted of a second and third type of rays. One of those was deflected by a magnetic field (as were the familiar " canal rays") and could be identified with Rutherford's beta rays. The last type was a very penetrating kind of radiation which had not been identified before. Villard was a modest man and he did not suggest a specific name for the type of radiation he had discovered. In 1903, it was

Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson (30 August 1871 – 19 October 1937) was a New Zealand physicist who was a pioneering researcher in both Atomic physics, atomic and nuclear physics. He has been described as "the father of nu ...

who proposed to call Villard's rays ''

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

s'' because they were far more penetrating than the alpha rays and beta rays which he himself had already differentiated and named (in 1899) on the basis of their respective penetrating powers. The name stuck.

Later work

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 Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive Electric charge, charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged at ...

chamber for the dosimetry of ionizing radiation. He defined a unit of kinetic energy released per unit mass which was later renamed the roentgen.

Retirement and death

When Villard retired, he left Paris. He died in

Bayonne Bayonne () is a city in southwestern France near the France–Spain border, Spanish border. It is a communes of France, commune and one of two subprefectures in France, subprefectures in the Pyrénées-Atlantiques departments of France, departm ...

, France, on January 13, 1934.

References

External links

*
The discovery of gamma rays
* (fr

{{DEFAULTSORT:Villard, Paul Ulrich 1860 births 1934 deaths People from Lyon Metropolis 19th-century French chemists 19th-century French physicists Members of the French Academy of Sciences 20th-century French chemists 20th-century French physicists Scientists from Lyon