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Last Updated: Tuesday, 8 March, 2005, 17:40 GMT
A-bomb architect Hans Bethe dies
Hans Bethe, Cornell University
Bethe's greatest contribution came in the field of solar physics
Hans Bethe, who fled Nazi Germany to become a key figure in the development of the first atomic bomb, has died at his home in Ithaca, US, aged 98.

During WWII, Bethe joined the Manhattan Project at Los Alamos, New Mexico, US, where the nuclear weapon was developed.

After the war, he worked with Edward Teller on the hydrogen bomb, but later campaigned for the peaceful use and international control of nuclear power.

He was awarded a Nobel Prize for his work on energy production in stars.

Seeing that destruction, many of us came to the conclusion that it should never be done again
Hans Bethe

Bethe, who died on Sunday, was emeritus professor of physics at Cornell University in Ithaca, New York - the institution he joined in 1935 after leaving Germany.

He was born in Strasbourg on 2 July 1906, which was then part of Germany's Wilhelminian Empire. As a child, he was frequently sick, contracting tuberculosis at the age of 10.

After completing a PhD in theoretical physics in 1928, Bethe taught in Frankfurt, Stuttgart and Munich.

Manhattan Project

But while working at the University of Tubingen in 1933, the scientist - whose mother was Jewish - lost his post due to the rise of the Nazi regime.

He moved to England and lectured at Manchester and Bristol before joining Cornell's faculty.

During WWII, he took leave from his university to head the theoretical physics division for the Manhattan Project, the code name for the US effort to produce an atomic bomb.

Trinity, US Army
Trinity was the first successful atomic test
His recruitment by Robert Oppenheimer, director of the Los Alamos lab, angered Edward Teller the physicist who had helped Oppenheimer organise the project. Teller had himself coveted the theoretical physics post.

On 16 July 1945, the scientists successfully detonated a plutonium implosion device, generating the world's first nuclear explosion.

Bethe's division had to calculate how much material would have to be compressed by the implosion to ensure success. The work led directly to the two bombs that were later dropped on Japan.

In 1996, Bethe recalled his experiences at Los Alamos during a lecture at Cornell: "Two cities in Japan were destroyed. Seeing that destruction, many of us came to the conclusion that it should never be done again, and this is where I have been ever since," he told the audience.

But it was in the field of solar physics where Bethe made his greatest contribution to science, publishing a now seminal paper in 1938 on the theory of energy production in stars.

Bethe came up with his carbon-nitrogen-oxygen (CNO) cycle, the chain of fusion reactions which large stars use to convert hydrogen to helium, releasing prodigious amounts of energy in the process.

This work and the studies that supported it were to win him the Nobel Prize in 1967.

Bethe also made major discoveries in solar physics on how atoms are built up from smaller particles, on what makes dying stars explode and how heavier elements are produced from the ashes of these supernovas.

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