Ion dose

Physical size
Surname	Ion dose
Formula symbol	${\displaystyle J}$
Size and unit system unit dimension SI A · s · kg -1 I · T · M −1

The ion dose J is a physical quantity used to quantify ionizing radiation . It describes the electrical charge of the ions of the same sign, which are created in a certain mass by ionizing radiation.

scope of application

The ion dose was used in radiation protection until January 1, 1995 as a dose parameter to quantify external ionizing radiation . After this point in time, new dose measures proposed by the International Commission on Radiation Units and Measurements (ICRU) were used. This was preceded by a new dose concept proposed by the International Commission on Radiological Protection (ICRP) in 1977 for body doses based on the dose equivalent . For a transitional period, the ion dose for photon radiation was used in a modified form as the “photon equivalent dose” .

unit

The SI unit of the ion dose is coulombs per kilogram.

${\displaystyle [J]=\mathrm {\frac {C}{kg}} \ }$.

An older unit that was no longer used after January 1, 1995 is the " X-ray " (unit symbol R), defined as one electrostatic unit per cm ^{3 of} air. An X-ray corresponds to 2.58 10 ⁻⁴ C / kg. ${\displaystyle \cdot }$

Standard ion dose

The standard ion dose is the ion dose generated by ionizing radiation freely in air under the standard conditions of 18 ° C and 760  Torr . ${\displaystyle J_{\mathrm {S} }}$

The following applies to the standard ion dose in free air:

${\displaystyle J_{\mathrm {S} }={\frac {\mathrm {d} Q}{\mathrm {d} m_{\mathrm {L} }}}={\frac {1}{\rho _{\mathrm {L} }}}\ {\frac {\mathrm {d} Q}{\mathrm {d} V}}\ }$.

${\displaystyle \mathrm {d} Q}$is the electrical charge of the ions of a sign that is generated per mass element of air in the volume element with the specific density . ${\displaystyle m_{\mathrm {L} }}$ ${\displaystyle \mathrm {d} V}$ ${\displaystyle \rho _{\mathrm {L} }}$

Magnitude

The standard ion dose is not an equivalent dose in the sense of the dose concept of today's radiation protection. It can best be compared with the absorbed dose on which the dose equivalent is based. In air under standard conditions , an average energy of about 34 eV is required to form an ion pair, each with an elementary charge e . In order to generate 1 C free ions of the same sign (corresponding to ion pairs), an energy of 34 joules is required. If this is related to 1 kg of air, the result is that a standard ion dose of 1 C / kg corresponds to an absorbed dose of 34 joules / kg (34  Gy ). A standard ion dose the size of the old unit 1 R would correspond to about 9 mGy. ${\textstyle {\frac {\mathrm {C} }{\mathrm {e} }}}$ ${\textstyle \,1\;\mathrm {eV} =\,1\;\mathrm {e} \cdot {\frac {\mathrm {J} }{\mathrm {C} }}}$

See also

• Radiation dose

swell

• Physikalisch Technische Bundesanstalt, "New dose parameters in radiation protection", PTB report Dos-23, Braunschweig, July 1994, pdf download , 977 kB

Individual evidence

1. ↑ M. Boutillon and A.-M. Perroche-Roux, Re-evaluation of the W value for electrons in dry air , Phys. Med. Biol. 32 p. 213, 1987 online