Re: Differences in Flux and Dose Equivalent Errors in USRTRACK

Lewis,

in the 41.sum.lis, the fluences are weighted with fluence-to-dose-equivalent
conversion coefficients, which have larger values at some energies than at
others. Depending on the shape of the neutron fluence spectra, some neutrons
contribute much to dose, and other neutrons less.
To simplify, suppose that the conversion coefficients be very large at high
energies and very small at low energies. And suppose the spectra be very
rich in low-energy neutrons and very poor in high-energy neutrons.
Then the response in 41.sum.lis, and its standard deviation, would be affected
mainly by the number of high energy neutrons, while the response of 31.sum.lis,
and its standard deviation, would be affected mainly by the number of
low energy neutrons.
This is a very exaggerated picture, but it shows that in principle the two
standard deviations do not need to be equal.

I have written the above assuming that you were comparing the standard
deviations of total dose and total fluence (both integrated over energy).
If you compare the standard deviations of dose and fluence in each of the 50
energy intervals, I expect the differences to be much smaller, since each
interval can be considered approximately monoenergetic.

Your USRTRACK and AUXSCORE input are correct.

Alberto

On Tue, 3 May 2011, Macfarlane, Lewis wrote:

> Alberto,
>
> Many thanks for your response. Apologies for my delay, I have been on holiday
> for a short while.
>
> In my AUXSCORE I have used WHAT(2) =utron and SDUM =B74. My USRTRACK,
> WHAT(2) was DOSE-EQ. I have attached my input file. I would have expected
> 31.sum.lis and 41.sum.lis to have the same standard deviations given that
> they should be the same results, albeit with the latter having flux-dose
> conversion factors applied. However they do not have the same standard
> deviations. I have attached the input file as suggested,
>
> Many thanks again!
> Lewis.
>
> -----Original Message-----
> From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Alberto Fasso'
> Sent: 21 April 2011 21:21
> To: fluka-discuss_at_fluka.org; Macfarlane, Lewis
> Subject: Re: Differences in Flux and Dose Equivalent Errors in USRTRACK
>
> Lewis,
>
> in your USRTRACK detector, did you put WHAT(2)=DOSE-EQ?
> in your AUXSCORE card, did you put WHAT(2)=NEUTRON and SDUM=AMB74,
> or WHAT(2) blank and SDUM=AMB7?
> In the second case, you would get dose equivalent for all particles,
> as you suggest.
>
> But it is always difficult to answer questions if the user doesn't send the
> input file
>
> Alberto
>
> On Thu, 21 Apr 2011, Macfarlane, Lewis wrote:
>
>> Dear Experts,
>>
>> In a recent FLUKA case I have undertaken, I've scored both neutron
>> fluence and neutron dose equivalent in the same geometry region, using
>> USRTRACK.
>>
>> I have used two separate USRTRACK cards with different names. The first
>> scores neutron fluence. The second scores dose equivalent and applies
>> AMB74 flux-dose conversion factors for neutrons only through an AUXSCORE
>> card. I ran the case for 10 cycles, 1.e7 primary particles per cycle.
>> The sources is a proton beam with a rectangular spectrum, energy range
>> 190-210 MeV.
>>
>> Upon viewing the results, I noticed that the 2 USRTRACKS had very
>> different associated standard deviations when I would expect that
>> neutron fluence and neutron dose equivalent should have the same
>> standard deviation as the only difference is the application of
>> fluence-dose equivalent conversion coefficients! Can anyone tell me the
>> reason why this is the case? I'm suspecting maybe the standard deviation
>> in the dose equivalent output is in fact for all particles, whereas the
>> result has been filtered for neutrons only, is =
>> this the case?
>>
>> Many thanks,
>> Lewis MacFarlane.
>
>

-- 
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