"Exposure" reflects the extent of ionization events taking place when air is irradiated by ionizing photons (gamma radiation and/or x rays). In photography, exposure is the amount of light allowed to fall on each area unit of a photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.
Applicable units are those of quantitykind:ElectricChargePerMass
http://hps.org/publicinformation/ate/faqs/gammaandexposure.html
http://en.wikipedia.org/wiki/Exposure_%28photography%29
http://dbpedia.org/resource/Exposure
"Exposure" reflects the extent of ionization events taking place when air is irradiated by ionizing photons (gamma radiation and/or x rays). In photography, exposure is the amount of light allowed to fall on each area unit of a photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.
For X-or gamma radiation, $X = \frac{dQ}{dm}$, where $dQ$ is the absolute value of the mean total electric charge of the ions of the same sign produced in dry air when all the electrons and positrons liberated or created by photons in an element of air are completely stopped in air, and $dm$ is the mass of that element.
http://www.iso.org/iso/catalogue_detail?csnumber=31895