Rutherford (unit)

Last revised by Daniel J Bell on 5 May 2021

The rutherford (symbol Rd) is an obsolete unit of radioactivity which was superseded by the introduction of the becquerel in 1975. One rutherford was equivalent to 1,000,000 nuclear disintegrations per second, or alternatively one becquerel equated to one microrutherford (μRd). 


As for all other eponymous units when the name is written out in full it is not capitalized, but its symbol is capitalized.

History and etymology

The rutherford was introduced to replace the curie which was felt to be an impractical unit. It was introduced by I F Curtis and E U Condon in 1946, and in 1949 its official use was ratified by the National Research Council of the USA 3. It never gained wide acceptance as a unit, and the curie remained the preferential unit for radioactive decay until the becquerel was adopted in 1975.

Interestingly the "Rutherford unit (RU)" had already been proposed as a unit of atomic distance by physicists, whereby 1 RU was defined as equal to 1 x 10-13 m  4,5.

It was named after the New Zealand physicist, Lord Ernest Rutherford (1871–1937) 2.

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