Answer to Question #445 Submitted to "Ask the Experts"

Category: Doses and Dose Calculations — External dose calculations

The following question was answered by an expert in the appropriate field:

We are two Italian students in Physics, and we have the following question: If we have the gamma photons flux (expressed in photons/s/GeV), is it possible to relate this flux with the absorbed dose (for example in mammals)? Best regards, P. Potenza & D. Orlando

Yes. If you know the incident gamma energy spectrum (given in photons/s/Gev), you can calculate the absorbed dose rate using energy/dose conversion factors given in Table !-4 of ICRU Publication 39, Determination of Dose Equivalents Resulting from External Radiation Sources, February 1985. These conversion factors are given in Gy/photon/Gev.

A convolution integral of S(E)D(E) over the range of energies covered by your gamma spectrum will give you the absorbed dose rate in Gy/s. S(E) is the differential gamma energy spectrum in photons/s/Gev, and D(E) is the differential ICRU conversion factors in Gy/photon/Gev. Multiplying the calculated dose rate by the time period of interest will give you the absorbed dose in Gy.

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