RE: [fluka-discuss]: USRBDX Neutron-Energy

From: Joachim Vollaire <>
Date: Mon, 18 Dec 2017 10:30:04 +0000

Hello Konstantin
To reduce the interaction length for nuclear inelastic interactions by for example a factor 50 (typical value used for such problem) you can use the following it your target is made of TUNGSTEN.
If you want the biasing to be applied only to primary photons, then you have to specify SDUM = INEPRI…
Concerning the scoring, the following should work, as you beam energy is equal to 15 MeV I have score the spectra using the energy boundary of the neutron groups for transport up to 20 MeV. It should eventually be increased with the number of bins if you go above in another problem. I have not manually specified the surface between Tung and AIR (you should or consider it in the normalization)
USRBDX 99. NEUTRON -31. Tung AIR 1.Neutron
USRBDX 0.02 1E-14 260. &

Finally, I would like to correct something in my previous reply, in fact, as correctly pointed out by one of my colleague, you can use the generalised particle ENERGY to calculate the energy fluence going through a surface separating two regions (practically this would be useful to do the accounting of energy entering a region and exiting it in some cases…)
Hoping this help

From: Konstantin Rönsch []
Sent: 16 December 2017 13:00
To: Joachim Vollaire <>;
Subject: Re: [fluka-discuss]: USRBDX Neutron-Energy

Hello Joachim,

thanks for your answer. So i detect the neutron spektra via USRBDX Part:Neutron .

And now i use the LAM_BIAS Card with SDUM = GDECAY, and the settings seen in the picture below. Is this the right way for my simulation?

Based on your advice to set the binning structure manually and to use logaithmic bins for neutrons spectra scoring, how can I realize it in the simulation?


Thanks for your answer and help.
Am 16.12.2017 um 12:23 schrieb Joachim Vollaire:
Hello Konstantin
A few things looking at your input. As you are using an electron beam and you want to see neutrons from photonuclear reactions it is recommended to add a LAM-BIAS card to increase the probability of nuclear reactions (FLUKA will correct the weight of generated particles accordingly). See the corresponding part of the manual.
Concerning the scoring, USRBDX is a surface crossing estimator (shared surface between adjacent regions), so it does not make sense to use the generalized particle ENERGY which corresponds to energy deposited along tracks not at surface crossing. The filtering with AMB74 does not make sense either as this is usually used for dose equivalent scoring (generalized particle DOSE-EQ) to select the desired dose equivalent conversion factor (folded with the fluence from track length estimators -> USRTRACK/USRBIN…).
So the first card is the correct approach. Note that the binning structure below 20 MeV will not be linear as you request but it will correspond to the boundaries of the 260 energy groups used for neutron transport below 20 MeV. It is suggested to manually set the binning structure (upper limit in that case) and use logarithmic bins for neutrons spectra scoring.
Hoping this help

From:<> [] On Behalf Of Konstantin Rönsch
Sent: 15 December 2017 20:33
Subject: [fluka-discuss]: USRBDX Neutron-Energy

Dear Fluka experts,
with Fluka i simulate an elektron beam on a tungsten target and i want to detect the energy spectrum of the neutron radiation between the materials tungsten and air.
I use the Card USRBDX to detect the spectrum, but i am not shure which settings are correct for my example. I simulate USRBDX for Neutrons and in an other card USRBDX with energy and a AUXSCORE card to filter the neutron part of the energy. So which way is the correct, or what are the differents, because the results are not exactly the same.
Thanks for help

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Received on Mon Dec 18 2017 - 12:51:02 CET

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