Sunday, September 6, 2009

Deceased--Louis Rosen

Louis Rosen
June 10th, 1918 to August 15th, 2009

"Louis Rosen, 91, Dies; Worked on First Nuclear Bombs"


Douglas Martin

September 6th, 2009

The New York Times

On May 9, 1951, on a coral atoll in the Pacific, scientists ignited what they hoped would be the first man-made thermonuclear reaction, the basis of the hydrogen bomb. A fireball rose 1,800 feet.

But the explosion alone, awe-inspiring though it was, was not enough to convince one eyewitness, Edward Teller, considered the father of the H-bomb, that thermonuclear fusion had indeed occurred. For that he had to wait for the results of a test devised by two young fellow physicists who worked with him at Los Alamos, N.M., where the first atomic bombs had been built.

At 5:30 the next morning, one of those colleagues, Louis Rosen, told Dr. Teller the exhilarating news: yes, fusion had been achieved. Dr. Teller promptly raced out to pay off a $5 bet.

He had bet against himself, wagering with a colleague that fusion would not occur.

Dr. Rosen died on Aug. 15 in Albuquerque at the age of 91; his granddaughter, Ambyr Hardy, said a subdural hematoma was the cause.

He was one of the last surviving links to the scientific giants who had created the atomic age — men like J. Robert Oppenheimer and Enrico Fermi as well as Dr. Teller. But more than that, he had also advanced the era.

Dr. Rosen was a lifer at Los Alamos. Where other scientists drifted away, he spent his career there, and built the most intense atom smasher in the world. He was also part ambassador, part lobbyist for the Los Alamos National Laboratory, promoting its continuing importance as a center not only of weapons development but also of basic research.

His atom smasher was his most spectacular project. “This monstrous gadget will give us new windows on the nucleus, a new set of probes,” he said in an interview with The New York Times.

Existing accelerators at the time smashed a high-speed beam of protons or electrons into a target. The resulting debris of subatomic particles would yield information on the composition of the nucleus. Dr. Rosen’s machine used the beam of protons to create a secondary, highly intense beam of particles called pi mesons, or pions.

When smashed into the target material, the meson beam — 1,000 times as intense as that of any existing accelerator — could be used as a probe to study how pions interact with other nuclear materials. The continuous interchange of pions between proton and neutron is part of the glue holding the nucleus together.

By contrast, higher-energy but less intense accelerators obliterated more of the nucleus but could not study the same kind of internal nuclear dynamics.

Another scientist at the time compared the two kinds of accelerator this way: think of the earlier version as hitting the nucleus with a baseball bat, and Dr. Rosen’s as doing so with a rapier.

In an article in Physics Today in 1966, Dr. Rosen called his machine “a badly needed bridge between nuclear and subnuclear physics.”

In the 1990s, after Dr. Rosen had formally retired but remained involved in decision making, the group at Los Alamos in charge of the accelerator shifted course, in line with changing directions in physics. No longer did it harvest pions. Instead, it concentrated on neutrons, which were being used in more and more basic research and in practical applications.

One application was to probe stockpiled nuclear weapons that could no longer be tested. Other applications included studying the structure of complex biological molecules and re-examining the nuclear fuel cycle. In particular, Los Alamos became known for testing neutrons in very cold temperatures — a tiny fraction of a degree above absolute zero.

Louis Rosen was born in Manhattan, earned bachelor’s and master’s degrees from the University of Alabama, and a doctorate in physics from Pennsylvania State University. He said he never took a course in nuclear physics.

With his doctorate he went directly to Los Alamos to join the Manhattan Project, the code name for the group of scientists, mathematicians and engineers who built the first nuclear bombs. He worked at the laboratory until two days before his death.

Dr. Rosen’s wife of more than 60 years, the former Mary Terry, died in 2004. He is survived by his brother, Bernard; two grandchildren; and four great-grandchildren.

After the war, as many scientists began to leave Los Alamos, Dr. Rosen set about trying to retain as many as he could as well attract top-level replacements. It was partly with this in mind that he and Norman Bradbury, the laboratory’s director, came up with the idea of the accelerator. Dr. Rosen lobbied federal agencies and members of Congress alike for support.

Writing in 1983 in Los Alamos Science, Dr. Rosen recalled a visit by the comptroller of the Atomic Energy Commission, who spotted him in the audience.

“Ah, Louis Rosen is here,” the official said. “Every time I talk to him it costs me a million dollars.”

Louis Rosen home page

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