He is one of the British scientists who participated in the United States' Manhattan Project, Britain's Tube Alloys, and was involved in nuclear weapon development.

During World War II Moon was part of the MAUD Committee that confirmed the feasibility of an atomic bomb and then became part of the British delegation to the Manhattan Project, where amongst other things he did work on designing instrumentation for measuring the eventual bomb test.

[2] After the war he was made Poynting Professor of Physics at Birmingham in 1946, succeeding Oliphant but receiving the appointment only after the first choice (Cecil Powell) had been rejected at the last minute for being a communist.

In 1950 Moon was the first person to detect gamma ray fluorescence; however his results were not considered statistically significant enough and it would be several years before they were proven.

Moon was invited to become the honorary life president of the Poynting Physical Society, at the University of Birmingham, in 1975.