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

From: <wurth_at_ipno.in2p3.fr>
Date: Wed, 11 May 2011 15:00:06 +0200

Hello everybody,

Sorry my last forwarded mail was a draft never sent to Alberto, it
contains some (too) late thoughts and is absolutely not relevant, this
is the real mail sent to Alberto Fasso the next day.

I did some forward to our last week discussion. Mr Fasso meant and I
agree that it could be some interest to some people.
Sorry for the cumulative mails if you are not interested.

I'm still looking for an even approximate composition of plain aluminum
paper or the special one which wraps some TLD dosimeters.

Best regards.


-------- Message original --------
Sujet: Re: Dosimetry simulations : composition of materials of interest
and results ?
Date : Fri, 06 May 2011 08:55:14 +0200
De : Sébastien Wurth<wurth_at_ipno.in2p3.fr>
Pour : Alberto Fasso'<fasso_at_slac.stanford.edu>


Thanks for the lecture, it helps but arises some other questions (sorry).
Maybe I can switch back to the discuss in order to stop pestering you.

All right, I could do some tests as you adviced and I will. It don't cost much and is always useful.
This will indeed settle the case of the surroundings materials.

About dose now :

I quote wikipedia : "This equilibrium occurs when a material is underirradiation and results in a constantcharge."

Ok, my materials are under (constant) irradiation : I posted an attached plot from my previous tests at E=200 keV.
One can see that the tin filter(d=5.75) as a dose approximately 10 times superior than the RPL glass just behind (d=2.61).

If there is charged particule equilibrium and the dose is independant of density how can I explain the difference?

Of course there is a particle fluence attenuation which is superior in tin than in glass but what about energetic fluence?

I'am going to read again my dosimetry courses...

Best regards.


Le 05/05/2011 22:55, Alberto Fasso' a écrit :
> Sebastien,
> 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,
> Alberto
> 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

Received on Wed May 11 2011 - 15:55:22 CEST

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