John Reginald Richardson (1912 in Edmonton, Alberta, Canada – 25 November 1997 in Fremont, California) was a Canadian-American physicist and one of the dominant figures in cyclotron development.

His many achievements include participation in the first demonstration of phase stability, the development of the first synchrocyclotron and the first sector-focused cyclotron.

From 1942 he worked on electromagnetic isotope separation for the Manhattan Project in Berkeley and Oak Ridge (calutron).

In 1946, after the discovery of the phase stability and the synchrotron principle by Weksler and Edwin McMillan, he collaborated with a group of physicists consisting of Ed Lofgren, Ken MacKenzie, Bernard Peters, Fred Schmidt and Byron Wright in converting the fixed-frequency 37-inch cyclotron at Berkeley to the first synchrocyclotron.

[2] An even bigger sector cyclotron with energies up to 520 MeV was built by Richardson's line at TRIUMF in Vancouver.