Editing Sievert (section)

===Operational quantities===
Operational quantities are measured in practice, and are the means of directly measuring dose uptake due to exposure, or predicting dose uptake in a measured environment. In this way they are used for practical dose control, by providing an estimate or upper limit for the value of the protection quantities related to an exposure. They are also used in practical regulations and guidance.<ref>ICRP publication 103, paragraph B147</ref>

The calibration of individual and area dosimeters in photon fields is performed by measuring the collision "air kerma free in air" under conditions of secondary electron equilibrium. Then the appropriate operational quantity is derived applying a conversion coefficient that relates the air kerma to the appropriate operational quantity. The conversion coefficients for photon radiation are published by the ICRU.<ref>''Measurement of H*(10) and Hp(10) in Mixed High-Energy Electron and Photon Fields.'' E. Gargioni, L. Büermann and H.-M. Kramer Physikalisch-Technische Bundesanstalt (PTB), D-38116 Braunschweig, Germany</ref>

Simple (non-anthropomorphic) "phantoms" are used to relate operational quantities to measured free-air irradiation. The ICRU sphere phantom is based on the definition of an ICRU 4-element tissue-equivalent material which does not really exist and cannot be fabricated.<ref>"Operational Quantities for External Radiation Exposure, Actual Shortcomings and Alternative Options", G. Dietze, D.T. Bartlett, N.E. Hertel, given at IRPA 2012, Glasgow, Scotland. May 2012</ref> The ICRU sphere is a theoretical 30&nbsp;cm diameter "tissue equivalent" sphere consisting of a material with a density of 1 g·cm<sup>−3</sup> and a mass composition of 76.2% oxygen, 11.1% carbon, 10.1% hydrogen and 2.6% nitrogen. This material is specified to most closely approximate human tissue in its absorption properties. According to the ICRP, the ICRU "sphere phantom" in most cases adequately approximates the human body as regards the scattering and attenuation of penetrating radiation fields under consideration.<ref>ICRP publication 103, paragraph B159</ref> Thus radiation of a particular energy fluence will have roughly the same energy deposition within the sphere as it would in the equivalent mass of human tissue.<ref name="IAEACalibration" />

To allow for back-scattering and absorption of the human body, the "slab phantom" is used to represent the human torso for practical calibration of whole body dosimeters. The slab phantom is {{nowrap|300 mm × 300 mm × 150 mm}} depth to represent the human torso.<ref name="IAEACalibration" />

The joint ICRU/ICRP proposals outlined at the 3rd International Symposium on Radiological Protection in October 2015 to change the definition of operational quantities would not change the present use of calibration phantoms or reference radiation fields.<ref name="endo" />