Rubby Sherr, 99, a Princeton University physics professor who helped develop the atomic bomb and witnessed its first test, died July 8 in Haverford, Pa.
The test took place near Alamogordo, N.M., on July 16, 1945. The United States dropped the first atomic bomb in wartime, over Hiroshima, Japan, on Aug. 6, 1945.
His major contribution was "the portion of the device positioned at the center of the bomb, designed to spread the nuclear chain reaction rapidly throughout the fissile plutonium material," son-in-law Robert Hess said.
Mr. Sherr was the co-inventor of the device, known as the Fuchs-Sherr Polonium-Beryllium neutron initiator, Mr. Hess said. Co-inventor Klaus Fuchs was convicted of espionage in Britain in 1950.
When he looked outside the bunker that had protected him from the blast, Mr. Sherr told a Princeton publication, "[I] thought, 'This is the greatest scientific experiment of all time.' "
"Then the horror sank in that the thing had actually worked, followed by relief that the atmosphere hadn't ignited, as some had feared it would."
Born in Long Branch, N.J., of Lithuanian immigrants, he graduated from Lakewood (N.J.) High School, earned a bachelor's degree in physics at New York University in 1934 and a doctorate in physics at Princeton in 1938.
In 1942, he joined the MIT-Harvard Radiation Laboratory, where he helped develop an airborne radar for detecting vehicle traffic.
"He spoke of testing the device while crammed into the rear fuselage of a small Army aircraft, flying high above a long, straight stretch of highway somewhere in New England," daughter Frances Sherr Ross said.
"The experience so terrified him that a decade passed before he flew again," she said.
Mr. Sherr became an assistant professor of physics at Princeton in 1946, associate professor in 1949, and professor in 1955.
From 1955 to 1971, he was principal investigator for an Atomic Energy Commission contract that supported "experimental and theoretical research in low energy nuclear physics," making him responsible "for the operation of the Princeton 18 Mev cyclotron," his son-in-law said.
His work resulted in the Princeton AVF cyclotron in 1970, Mr. Hess said.
Since September 1936, Mr. Sherr published more than 100 articles in scientific journals.