RE: Air dose to water dose conversion

From: Thomas Otto <>
Date: Mon, 21 Mar 2011 12:02:41 +0000

Hello Betrand,
I have little experience with secondary electron equilibrium in FLUKA,
there may be others who have an authoritative opinion on the concept.
In FLUKA, as in any other simulation code, the simplifications of
"nature", such as cut-off energies, will have an influence on the outcome
of calculations.

In measurement, however, an "equilibrium ionization chamber" must be as
large as the range of secondary electrons of the radiation it is considered
to measure. This is technically feasible for photon energies energies up
to approx 100 or 200 keV, afterwards the chambers would become too large
to operate. This only as a caveat about the size of the geometry you may
need to establish equilibrium !

Under secondary electron equilibrium, absorbed dose from photon radiation
at energy E in material N can be converted to absorbed dose in material M
by the ratio of mass-energy-transfer coefficients (mu_en(E,M)/rho):
D(E,M) =3D D(E,N) * (mu_en(E,M)/rho) / (mu_en(E,N)/rho)
The coefficients are tabulated by Hubbell and Berger and are reproduced
for a mall range of materials in many textbooks. For electrons (charged
particles in general), a similar relation with the mass-stopping
coeffients S is holding.

As for useful literature on fundamental concepts of dosimetry, try to find
a copy of Vol 1 of Attix, Roesch and Tochilin (eds.) "Radiation
Dosimetry", even if the quantities and units have other names today, the
discussion is chapter 1 by Roesch and Attix is very good. Another good
fundamental text is from Gudrun Alm Carlsson in Kase, Bjaerngard, Attix
(eds.) "The Dosimetry of ionizing radiation 1".

Best regards, Thomas

Thomas Otto
Safety Officer Technology Department
CH-1211 Geneve 23

Tel (+41)(0) 22 76 73272
GSM (+41)(0) 76 487 0648
Received on Mon Mar 21 2011 - 16:24:33 CET

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