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

Alberto,

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.

But assuming the electronic equilibrium, I can write :

Absorbed energy (D) = transfered energy (Kerma)

Or Kerma (K) is proportionnal to energetic fluence (F) : K =
(µtransfered/rhô)*F and D = K.

And here comes a Fluka question : I noticed that fluence calculations in
USRBIN classical detectors seems always to have a better convergence speed
(needs simply less statistics, less primaries) as dose calculation or
deposited energy for instance when you plot the results in flair or
pawlevbin+paw. Is this true or just an rather strange idea of mine ?

> 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
>>>
>>>
>>
>>
>>
>
> --
> Alberto Fasso`
> SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
> Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
> fasso_at_slac.stanford.edu
>
Received on Wed May 11 2011 - 15:35:03 CEST