Philip Morrison

Physicist who armed the first atomic bomb

On 12 July 1945 Philip Morrison removed two cases containing the plutonium core of a nuclear weapon from a safe at Los Alamos laboratory in New Mexico, loaded them in the back seat of a Dodge sedan and rode for five hours beside them to the remote test site of Alamogordo.

Philip Morrison, theoretical physicist and writer: born Somerville, New Jersey 7 November 1915; Lecturer, University of Illinois 1940-43; staff, Manhattan Project 1942-46; staff, Cornell University 1946-64; Visiting Professor, Massachusetts Institute of Technology 1964, Professor of Physics (Emeritus) 1965-2005, Institute Professor 1973-2005; married 1938 Emily Kramer (marriage dissolved), 1965 Phylis Hagen (died 2002); died Cambridge, Massachusetts 22 April 2005.

On 12 July 1945 Philip Morrison removed two cases containing the plutonium core of a nuclear weapon from a safe at Los Alamos laboratory in New Mexico, loaded them in the back seat of a Dodge sedan and rode for five hours beside them to the remote test site of Alamogordo.

Four days later, after helping insert the core in its massive housing, he retreated to a safe distance, lay on his stomach in the desert dust and watched through a welder's screen the "brilliant violet flash", as he described it, of the world's first atomic explosion.

Within three weeks he was on Tinian island in the Pacific, arming the bomb that would be used in anger over Nagasaki, and soon after that he was on the ground in defeated Japan viewing at first hand the destruction that had been wrought.

Morrison was a true witness to, and participant in, the birth of the nuclear age. A theoretical physicist, he was only 29 years old then, a polio victim who walked with a stick and - something known at the time to very few - a former member of the Communist Party. The remaining 60 years of his life, many of them spent as a professor at the Massachusetts Institute of Technology (MIT), were devoted to physics and astronomy, to sharp-eyed criticism of nuclear weapons and the arms race, and to the popularisation of science, for which he had an exceptional gift.

He survived the exposure of his Communist past in the McCarthyist 1950s, but as recently as five years ago was forced to deny (convincingly) a suggestion in a book that he had been a spy for the Soviet Union.

Born into a family of modest income in New Jersey in 1915, Phil Morrison grew up in Pittsburgh and was drawn to physics by a fascination for radio - he had a ham-radio licence at the age of 12. Graduating from a local university, he went to Berkeley to take his PhD under the charismatic Robert Oppenheimer in what in later years would be seen as a nest of left-wing activism, though in fact Morrison had joined the Communist Youth League in his Pittsburgh days. From Berkeley, marked out as a theorist of great talent, he went to teach at the University of Illinois, where at the end of 1942 he was drawn into the Manhattan Project, making the atomic bomb.

Though still young, he would take on several important roles. At first he did theoretical work for Enrico Fermi, who was building the first nuclear reactor in Chicago, and also analysed intelligence about the German nuclear effort; then he moved to Los Alamos where he was a close adviser to the director, Oppenheimer, and in the final stages had joint responsibility for the "active material" - the plutonium - in the implosion weapon.

This experience, and what he saw in Japan in September 1945, convinced him of the need to avoid future war and particularly atomic war and he was active in the Federation of Atomic Scientists, formed to press that case. He attracted early public notice, and official reproof, with a magazine article describing in vivid detail, as if it had just happened, the effects of an atomic explosion in Manhattan.

The education of the public in nuclear science, and later in science generally, became a mission. Over the years he wrote a lucid column and hundreds of book reviews for Scientific American, as well as several books, and with his second wife, Phylis, made and presented a successful television series in the 1980s called The Ring of Truth, explaining basic scientific principles and mysteries.

He continued to work in academic nuclear science, and increasingly in astrophysics and astronomy, where his most eye-catching contribution was to co-write, with Giuseppe Cocconi, a 1959 article pressing the case for an active search for radio signals from other planets. This was acted upon by Nasa and, though no alien message has yet been heard, the effort has provided the basis for several Hollywood films.

The charge of espionage against him surfaced in 1999 in a book called Every Man Should Try by Jeremy Stone, which linked an unnamed physicist who was unmistakably Morrison with a Soviet agent codenamed Perseus, who was never caught or conclusively identified. Morrison effectively killed off the theory by listing several practical reasons why he could not be Perseus.

Brian Cathcart