Fwd: Re: Dosimetry simulations : composition of materials of interest and results ?

From: <fasso_at_SLAC.Stanford.EDU>
Date: Wed, 11 May 2011 14:52:41 +0200


if you have charged particle equilibrium, the density of the material
is not critical.
Fano's theorem: In a medium of homogeneous atomic composition where is present
a primary uncharged radiation field of constant energy fluence, the energy
fluence of the secondary charged particles is also constant and independent of
medium density.
Qualitative proof: the number of secondaries released in volume element is
proportional to the material density, while their average range is inversely
proportional to it. Therefore their energy fluence (total energy-weighted path
length per cm3) is independent of density.
This is the reason why you can have a ionization chamber with walls having the
same composition as the filling gas, but of course much larger density.

I am not sure that this can help you, but if you can ensure charged particle
equilibrium (for instance wrapping the dosimeters with some material of
approximately the same composition) perhaps you can solve your problem.
In any case, you can do a test with FLUKA, simulating this situation
with different densities.

Meilleures salutations,


On Thu, 5 May 2011, wurth_at_ipno.in2p3.fr wrote:

> Alberto,
> You pointed out a major issue of mine.
> As I told you, I have the composition of the dosimeter materials
> silver-doped-glass for RPL and lithium fluoride for TLD with isotope ratio
> 7Li/6Li (not the natural one) plus several ppm of doping elements Mg, Cu,
> P. So I am using the most precise description I got.
> But, what about the materials surrounding these dosimeters ?
> Several mm of plastic with very various densities from 0.9 to 1.5 at least.
> Maybe I'm laking a little of physics knowledge here (it is quite possible)
> but I believed that in matter of deposited energy the density of the
> material is really the relevant data assuming of course that the materials
> are similar (dealing mostly with C,N,O,H in various quantities).
> Especially in some low energy EM problem like mine.
> I asked the same question I first asked today on the list about ABS resin
> to (I believed) the proper person to the french institute of radiation
> safety and radioprotection which is the "provider" of the RPL dosimeter
> and surroundings, well just say that I liked your answer more...
> And I am sure they conducted simulations too, so someone there did have
> those issues at the time.
> Anyway,
> Best regards.
> Arrivederci.
> Sebastien.
>>> Indeed I saw in the paper you linked that RPL glass could be replaced by
>>> plain aluminum, results (considering deposited energy or dose) would not
>>> change a lot.
>> Yes, but remember that the benchmark to which that paper referred was done
>> with a high energy hadron cascade, containing all kinds of particles at
>> all kinds of energies. I am not sure that the same could be assumed in a
>> low energy problem as yours seems to be.
>> Alberto

Alberto Fasso`
SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
Phone: (1 650) 926 4762   Fax: (1 650) 926 3569
Received on Wed May 11 2011 - 15:35:16 CEST

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