Wheel (unit)

Physical unit
Unit name	wheel
Unit symbol	${\displaystyle \mathrm {rd} }$
Physical quantity (s)	Absorbed dose
Formula symbol	${\displaystyle D\,}$
dimension	${\displaystyle {\mathsf {L^{2}\;T^{-2}}}}$
In SI units	${\displaystyle \mathrm {1\,rd=0{,}01\;Gy} }$

The wheel ( unit symbol rd ), from engl. r adiation a bsorbed d ose , is no longer used since 1977, in the medical field since the end of 1985 unit of absorbed dose of radiation , or more precisely the energy dose . It was replaced by the SI unit Gray and has not been a legal unit in Germany since January 1, 1978.

In 1953 the ICRU defined the wheel as the unit of absorbed dose to be 100  erg / g, which is equivalent to:

${\displaystyle \mathrm {1\,rd=0{,}01\,Gy=0{,}01\,{\frac {J}{kg}}} }$

The unit symbol rd should not be confused with the identical unit symbol for Rutherford , an outdated unit of activity . The unit symbol rad was also used, but is identical to the unit symbol rad for plane angles .