Dose rate constant

Under dose rate constants ( English absorbed dose constant ) is defined as calculated for radionuclides specific physical constants in radiation protection or dosimetry . They are used to establish a relationship between the activity of radioactive emitters and the radiation doses generated by them at a certain distance .

It is generally assumed that:

the radiation source is punctiform
the weakening of the beam, d. H. Absorption and scattering is negligible
the square law of distances .

The symbol is usually the large gamma , the SI unit is Gy · m ² · s ⁻¹ · Bq ⁻¹ . ${\ displaystyle \ Gamma}$

Dose rate for gamma emitters

The dose equivalent rate takes into account the biological effectiveness of radiation. For gamma emitters it can be estimated using the following formula:

${\ displaystyle {\ dot {H}} = \ {\ frac {\ Gamma _ {H} \ cdot A} {r ^ {2}}}}$

${\ displaystyle {\ dot {H}}}$ is the dose equivalent rate
${\ displaystyle \ Gamma _ {H}}$ is the equivalent dose rate constant
r is the distance from the radiation source
A is the activity of the gamma emitter

${\ displaystyle {\ dot {H}}}$ is a function of the decay energies, the transition probabilities and the mass attenuation coefficient of the absorbing object. The following table lists some examples of . ${\ displaystyle \ Gamma _ {H}}$

Radionuclide	${\ displaystyle \ Gamma _ {H}}$ (mSv m ² h ⁻¹ GBq ⁻¹ )
⁶⁰Co *	0.354
²²⁶Ra * + daughter	0.221
Positron emitter **	~ 0.16-0.18
¹³⁷Cs *	0.0927
¹³¹I *	0.066
¹²³ I.	0.0465
^99mTc	0.0216

* Not a pure gamma
emitter ** Pair annihilation radiation

This means for example:

For one hour of irradiation from a source with 1 GBq ⁶⁰Co , an equivalent dose of a maximum of 0.35 mSv can be expected at a distance of one meter .

Others

The so-called gamma ray constant is obsolete. It does not take into account components from characteristic radiation .

For beta emitters , a special dose rate function is used instead of the constant.

In addition, there are also dose rate constants for X-ray sources , but here the relationship to the tube current is established.