In December 1942 he was the man who stood ready with an axe to cut the scram line during the start up of Chicago Pile-1, the world's first nuclear reactor to achieve criticality.

[1][2] He earned his Doctor of Philosophy (Ph.D.) from the University of Chicago in 1941, writing his thesis on "Extensive cosmic-ray showers and the energy distribution of the primary cosmic rays".

Because of fears that the reaction could "run away", Hilberry stood ready with an axe to cut the scram line, a manila rope connected to control rods that could quickly shut the reactor down.

He was the first director of Argonne's International School of Nuclear Science and Engineering, an important part of the Eisenhower Administration's Atoms for Peace program, from 1955 to 1956.

[1] Hilberry was the recipient of the American Nuclear Society's Arthur Holly Compton Award, and received a citation for meritorious service from the Atomic Energy Commission.