Hal Gray worked at the Cavendish Laboratory, Cambridge, UK with Rutherford (1927-1932) on the absorption of gamma rays in matter. This research resulted in the Bragg-Gray principle, the application
of which enabled the measurement of energy imparted and absorbed dose. That is why the gray was proposed as the special name for the SI derived unit associated with these quantities by the
International Commission for Radiation Units and Measurements (ICRU) of which Hal Gray was a former Vice-Chairman.
The Consultative Committee for Units (CCU) accepted this
proposal in 1974 (Recommendation U 1 (1974)). Subsequently, the 15th General Conference on Weights and Measures (CGPM) adopted the special name gray, Gy, to be included in the SI in 1975
(Resolution 9). Indeed, Gray's name is also commemorated in the Gray Laboratory for radiobiology research based at Mount Vernon Hospital in the UK (where he worked from 1933), in the Gray Trust
that sponsors a biennial Gray Conference, and in the Gray Medal awarded by the ICRU. For biographies see ICRU News June 1997, the Royal Society Biographical Memoirs, and the websites of the Gray Laboratory and the Gray Cancer Institute.