John F. Allen (physicist) facts for kids

John Frank Allen (May 5, 1908 – April 22, 2001) was a brilliant Canadian physicist. He was also known as Jack Allen. He is famous for discovering superfluidity in liquid helium. This happened in 1937, at the same time as another scientist, Pyotr Leonidovich Kapitsa, made the same discovery in Moscow. Allen worked with his student Don Misener in Cambridge, England.

Early Life and Education

John Allen was born in Winnipeg, Canada. His father, Frank Allen, was also a physics professor. John followed in his father's footsteps.

Studying Physics

John Allen first studied physics at the University of Manitoba. He earned his first degree there in 1928. Then, he moved to the University of Toronto for more advanced studies.

PhD Research

In Toronto, he earned his master's degree in 1930. He then started his PhD, working with John Cunningham McLennan. His research focused on superconductivity. This is a special state where some materials can conduct electricity with zero resistance.

During his PhD, Allen built his first cryostat. This is a special machine that can make things extremely cold. His professor even used it for a public demonstration in London. Allen finished his PhD in 1933.

Postdoctoral Work and Discovery

After his PhD, Allen received a special fellowship. He used it to work at Caltech in the United States from 1933 to 1935.

Joining Mond Laboratory

In 1935, Allen moved to the Mond Laboratory in Cambridge, England. He planned to work with Pyotr Kapitsa on experiments at very low temperatures. However, Kapitsa was unable to return from a trip to the Soviet Union.

So, John Allen continued his research on his own. He studied how helium behaves at super cold temperatures.

Discovering Superfluidity

In 1937, Allen and his student Don Misener made an amazing discovery. They found that liquid helium could become a "superfluid". This means it can flow without any friction, like it's defying gravity! Their findings were published in a science journal in 1938. Even though Allen discovered it independently, the Nobel Prize for superfluidity was later given only to Kapitsa.

Career and Contributions

Allen stayed in Cambridge until 1947. Then, he became a professor at the University of St Andrews in Scotland.

Leadership at St Andrews

At the University of St Andrews, Allen was a leader. He was the dean of the Faculty of Science twice. He also helped create a new Faculty of Applied Science in Dundee. He oversaw the building of a new science complex in St Andrews, which opened in 1966.

In 1949, he was recognized for his work and became a Fellow of the Royal Society.

Later Years and Retirement

Allen was also involved in international physics groups. He led the Very Low Temperature Commission for the International Union of Pure and Applied Physics. He retired in 1978 but remained a professor emeritus until he passed away.

He received an honorary doctorate from Heriot-Watt University in 1984. The physics building and library at the University of St Andrews are named after him. John Allen passed away on April 22, 2001, from a stroke.

Family Life

John Allen married Elfriede Hiebert in 1933. They later divorced and had one adopted son.

Amazing Scientific Work

John Allen was not just a discoverer; he was also an inventor. He developed many useful techniques for working with very cold temperatures.

Key Inventions

• In 1937, he introduced the O-ring. This is a simple but important seal used in vacuum systems.
• In 1947, he invented indium gaskets. These are special seals that prevent leaks in super cold environments.

More Superfluid Discoveries

Allen's student, Ernest Ganz, later observed "second sound" in liquid helium. This is a special type of heat wave that travels through superfluids. Allen and his team might have also measured "third sound" in thin films of helium, but they didn't publish these results.

Wartime Contributions

During World War II, Allen used his physics skills to help. He worked on projects for the army. This included designing oxygen generators for bomber planes. He also helped develop special fuses for anti-aircraft shells.

Filming Physics

Allen was also a pioneer in using movie cameras for science. In 1938, he filmed the amazing "superfluid helium fountain." He used a pocket flashlight to make it visible.

He spent ten years making a film about the strange behaviors of liquid helium-4. It was hard to film because liquid helium is clear. This unique color movie is one of his great gifts to physics. He showed how moving images could teach students and the public about science.

Pitch Drop Experiment

Around 1984, Allen even updated the famous St. Andrews pitch drop experiment. This experiment shows how a very thick liquid, like tar, can flow over many years.

See also

• Timeline of low-temperature technology

• John Allen's video on superfluid helium

Images for kids

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  J F Allen building, hosting the School of Physics and Astronomy of the University of St Andrews

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  Helium liquifier built by John F. Allen in 1952 at the University of St Andrews