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 scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

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 γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

in 1900 while studying the radiation emanating from

radium Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rat ...

Early research

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

Rhône The Rhône ( , ; wae, Rotten ; frp, Rôno ; oc, Ròse ) is a major river in France and Switzerland, rising in the Alps and flowing west and south through Lake Geneva and southeastern France before discharging into the Mediterranean Sea. At Ar ...

. He graduated from the

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

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 and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. Si ...

. 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 from

salts that escaped from a narrow aperture in a shielded container onto a photographic plate, through a thin layer of

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...

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 An anode ray (also positive ray or canal ray) is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886. Late ...

") and could be identified with Rutherford's

beta rays A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β� ...

. 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 came to be known as the father of nuclear physics. ''Encyclopædia Britannica'' considers him to be the greatest ...

who proposed to call Villard's rays ''

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

s'' because they were far more penetrating than the alpha rays and

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 Radiation dosimetry in the fields of health physics and radiation protection is the measurement, calculation and assessment of the ionizing radiation dose absorbed by an object, usually the human body. This applies both internally, due to ingested ...

, 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 charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...

chamber for the dosimetry of ionizing radiation. He defined a unit of

kerma Kerma was the capital city of the Kerma culture, which was located in present-day Sudan at least 5,500 years ago. Kerma is one of the largest archaeological sites in ancient Nubia. It has produced decades of extensive excavations and research, ...

which was later renamed the roentgen.

Retirement and death

When Villard retired, he left Paris. He died in

Bayonne Bayonne (; eu, Baiona ; oc, label= Gascon, Baiona ; es, Bayona) is a city in Southwestern France near the Spanish border. It is a commune and one of two subprefectures in the Pyrénées-Atlantiques department, in the Nouvelle-Aquitaine r ...

, France, on January 13th, 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