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Basic dosimetric quantities

Absorbed dose

Absorbed dose is one of the fundamental dosimetric quantities in radiation protection. It is a physical quantity to measure radiation energy absorbed by unit mass of materials.

Definition: Energy absorbed per unit mass of the material
   
Unit: Gray (Gy)

Equivalent dose

Biological effects are attributed not only to the absorbed dose but also depend on the type and energy of the radiation. Equivalent dose is a physical quantity to measure the effect to a tissue or organ by different types and energies of radiation.

Definition: For a particular type and energy of radiation, equivalent dose is the absorbed dose averaged over a tissue or organ and weighted for the radiation quality that is of interest. The weighting factor for this purpose is called "radiation weighting factor", which reflects the severity of biological effects due to different types and energies of radiation. When the incident radiation field consists of different types and energies of radiation, the equivalent dose in a tissue or organ is equal to the sum of the weighted absorbed doses.
   
Unit: Sievert (Sv)

Type of radiation
Energy of radiation
Radiation weighting factor
Photons
All energies
1
Electrons and muons
All energies
1
Neutrons
<10keV
5
10~100keV
10
>100keV~2MeV
20
>2MeV~20MeV
10
>20MeV
5
Protons (except recoil protons)
>2MeV
5
a particles, fission fragments, heavy nuclei
-
20


Effective dose

Biological effects also depend on the type of tissue or organ that has been irradiated. Effective dose is to quantify the total detriment from exposures of several organs or tissues.

Definition: Effective dose is the sum of the weighted equivalent doses in all the tissues and organs of the body. The factor by which the equivalent dose in tissue or organ is weighted is called "tissue weighting factor", which represents the relative contribution of that organ or tissue to the total detriment resulting from uniform irradiation of the whole body.
   
Unit: Sievert (Sv)

Tissue or organ
Tissue weighting factor
Gonads
0.20
Bone marrow (red)
0.12
Colon
0.12
Lung
0.12
Stomach
0.12
Bladder
0.05
Breast
0.05
Liver
0.05
Oesophagus
0.05
Thyroid
0.05
Skin
0.01
Bone surface
0.01
Remainder
0.05

(Source : 1990 Recommendations of the International Commission on Radiological Protection (ICRP Publication No. 60))

 

 

 


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Last revision date: <19 Dec 2012>