Air dose to water dose conversion

From: Bertrand H. Biritz <>
Date: Thu, 17 Mar 2011 21:02:49 -0400

Dear FLUKA forum,

I have a basic question regarding the applicability of a paragraph
I read in the NCRP report 151. There they mention
...the result from an instrument calibrated for exposure [in roentgen (R)]
is divided by 114 to obtain air kerma (Ka) (in gray), or by 104 to obtain
an acceptable approximation for absorbed dose (in gray) or dose equivalent
(in sievert) at a point in tissue.

I combined these two conversions to go from dose-to-air to dose-to-water.
For a simple simulation where I have a T=1 MeV electron beam hitting a
1cc of water the dose-to-air (if I replace the cube of water with air)
converted to dose-to-water is within 20-40% of what the USRBIN dose estimator
gives (the measured value is less than the converted one).
This is with PRECISIOn and using the EMFCUT option. Since I am new to
this I wasn't sure if this difference fell under the "acceptable approximation"
mentioned in the NCRP report.

When I run the actual simulation though the agreement between converted
dose-to-air for water and measured dose are off by about 90%, again with
the measured value being less. Is this because this time photon's with an
energy spectrum are hitting the water target? The basic set-up is a
mono-energetic T = 4 MeV electron beam hitting a tungsten target and then
the collimated beam of photons irradiates the water phantom.

Ultimately I was hoping to use a USRBIN EM-ENERGY estimator to measured
the deposited energy in the air surrounding the machine and then convert
that to dose-to-water to estimate the dose a person would receive if they
were standing a certain distance away from the machine. Is this the way
one would do it or am I going about this the wrong way?

Any insights would be greatly appreciated,
Received on Fri Mar 18 2011 - 10:09:44 CET

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