Absorbed dose

Surname

Absorbed dose

specific energy

${\ displaystyle D}$

Size and unit system	unit	dimension
SI	Gy	L ² · T ⁻²

The absorbed dose is a physical quantity which indicates the average energy that is given off by ionizing radiation to matter of the mass . It is the basis of dosimetry in the application of ionizing radiation and in radiation protection. In radiation protection, the absorbed dose is the basic parameter for determining the dose equivalent . ${\ displaystyle D}$ ${\ displaystyle E}$ ${\ displaystyle m}$

Calculation of the absorbed dose

Given the density of the material and the energy given off to the mass in the volume element , the absorbed dose is calculated as follows ${\ displaystyle \ rho}$ ${\ displaystyle \ mathrm {d} m}$ ${\ displaystyle \ mathrm {d} V}$ ${\ displaystyle \ mathrm {d} E}$

{\ displaystyle D \ = \ {\ frac {\ mathrm {d} E} {\ mathrm {d} m}} \ = \ {\ frac {1} {\ rho}} \ {\ frac {\ mathrm {d } E} {\ mathrm {d} V}}}

To evaluate energy doses, the material concerned must be known. The material dependency of the absorbed dose is based in particular on the different ionization energies of the atoms and molecules.

unit

The SI unit of the absorbed dose is the gray (Gy).

{\ displaystyle \ mathrm {1 \, Gy = 1 \, {\ frac {J} {kg}}}}

The unit wheel ( rd ) is obsolete . This designation stands for "radiation absorbed dose".

Measurement of the absorbed dose

The absorbed dose is determined by means of detectors that respond to energy-dependent physical radiation effects in the irradiated material, such as heat generation, ionization or the kinetic energy of generated charged particles. Are used z. B. calorimeters, ionization chambers and semiconductor detectors.

Energy doses when using ionizing radiation

Radiation therapy is an important application of ionizing radiation . Energy doses of up to 80 Gy are administered as a herbal dose. Such a high value can only be achieved by dividing this total dose into small daily individual doses of 1.8–2.5 Gy (fractionation).

In the case of food irradiation to reduce the germ load, energy doses of up to several kGy are administered.

Absorbed dose as a basic quantity in radiation protection

In radiation protection, the absorbed dose is the basis for the equivalent dose in the form of dose parameters and the non-measurable body doses . The relationship is expressed by quality factors or weighting factors. The type of radiation involved, on which the quality and weighting factors depend, also plays a role. In the calculation of dose parameters and body doses, the energy doses are therefore included separately according to the type of radiation ( or ). The index stands for "Radiation" for "Tissue" (usually the mean value over an entire organ). Compare the illustration in the article "Equivalent dose". ${\ displaystyle D_ {R}}$ ${\ displaystyle D_ {T, R}}$ ${\ displaystyle R}$ ${\ displaystyle T}$

Detectors for the absorbed dose are calibrated according to the dose measurement variables of the dose equivalent to be determined. The material dependency of the absorbed dose is taken into account in accordance with the ICRU using phantoms that, like biological soft tissue, absorb and scatter the radiation.

Only very high radiation exposures with energy doses above 1 Gy, where deterministic radiation effects are decisive, are described in radiation protection as energy doses instead of equivalent doses.

Absorbed dose rate

The absorbed dose rate expresses the change in the absorbed dose over time.

{\ displaystyle {\ dot {D}} \ = \ {\ frac {\ mathrm {d} D} {\ mathrm {d} t}} \}

The SI unit is watt / kg .

The absorbed dose rate is hardly used in practical radiation protection. For external radiation exposure, the dose rate used is instead the local dose rate , a dose measure of the dose equivalent.

swell

International Commission on Radiological Protection (ICRP): The 2007 Recommendations of the International Commission on Radiological Protection , ICRP Publication 103, 2007, German edition published by the Federal Office for Radiation Protection, Section 4 Variables used in radiation protection , ICRP Publication 103 , (PDF document, 2.2 MB)
ICRP: Conversion Coefficients for Radiological Protection Quantities for External Radiation Exposures , ICRP Publication 116, 2010, ( PDF document , 13 MB).
Physikalisch Technische Bundesanstalt, "New dose parameters in radiation protection", PTB report Dos-23, Braunschweig, July 1994, pdf download , 977 kB

Individual evidence

^ Nutrition review No. 6, B13, June 2007, download

[1] Nutrition review No. 6, B13, June 2007, download