Exposure has the dimension radiation per mass. The SI composite unit of exposure is the coulomb of radiation per kilogram.

Maple knows the units of exposure listed in the following table.

An asterisk ( * ) indicates the default context, an at sign (@) indicates an abbreviation, and under the prefixes column, SI indicates that the unit takes all SI prefixes, IEC indicates that the unit takes IEC prefixes, and SI+ and SI- indicate that the unit takes only positive and negative SI prefixes, respectively.  Refer to a unit in the Units package by indexing the name or symbol with the context, for example, roentgen[SI] or R[SI]; or, if the context is indicated as the default, by using only the unit name or symbol, for example, roentgen or R.

The unit of exposure is defined as follows.

A roentgen is defined as $0.000258$ coulomb of radiation per kilogram.

$\mathrm{convert}\left('\mathrm{roentgen}'\,'\mathrm{dimensions}'\,'\mathrm{base}'=\mathrm{true}\right)$

$\frac{\mathrm{electric\_current}\left(\mathrm{radiation}\right)\mathrm{time}\left(\mathrm{radiation}\right)}{\mathrm{mass}}$

$\mathrm{convert}\left(1\,'\mathrm{units}'\,'\mathrm{roentgen}'\,\frac{'C\left(\mathrm{radiation}\right)'}{'\mathrm{kg}'}\right)$

$\frac{129}{500000}$

$\mathrm{convert}\left(1\,'\mathrm{units}'\,'\mathrm{roentgen}'\,\frac{'C'}{'\mathrm{kg}'}\right)$

$\frac{129}{500000}$

$\mathrm{Units}\left[\mathrm{UseMode}\right]\left('\mathrm{standard}'\right)$

$\mathrm{simple}$

$\mathrm{convert}\left(1\,'\mathrm{units}'\,'\mathrm{roentgen}'\,\frac{'C'}{'\mathrm{kg}'}\right)$

Error, (in `convert/units`) unable to convert `R` to `C/kg`

$\mathrm{convert}\left(1\,'\mathrm{units}'\,'\mathrm{roentgen}'\,\frac{'C\left(\mathrm{radiation}\right)'}{'\mathrm{kg}'}\right)$

$\frac{129}{500000}$

$\mathrm{convert}\left(1\,'\mathrm{units}'\,'\mathrm{roentgen}'\,\frac{'C'}{'\mathrm{kg}'}\,'\mathrm{symbolic}'\right)$

$\frac{129}{500000}$