Bug in FLUKA or error in the setup?

From: Mina Nozar <nozarm_at_triumf.ca>
Date: Thu, 15 Aug 2013 12:19:22 -0700

Hello everyone,

There is something happening in my setup that just doesn't make sense
and I have tried different things in the last three days, trying to find
out whether the mistake is from my part.

I have 75 MeV electron beam 4x4 cm square incident on a Beam Dump
composed of Al with some cooling channels. We have divided up the BD
and some of the shielding around the BD into sub regions in order to use
the results for thermal analysis.

Here is the description of the strange behaviour (as best as I can
describe it). The beam spot area (BS) where the beam hits is at an
angle of 3.06 deg. wrt the horizontal plane. The BS is 74 cm long, 4 mm
high, and 4 cm wide. I have the BS divided up into 16 equal regions:
BS1-BS16 (see attachment please).

When I look at the Beam Particle distribution (usrbin), I see the beam
go through all of these regions as expected but when I look at deposited
energy in BS4, BS8, BS12, and BS16 (stacked up vertically), I see zero
deposited energy. When I look at beam particle and photon fluences in
these regions, I see distributions that make sense but nothing in BS4,
BS8, BS12, and BS16. How could this be???

Another related oddity is that I see similar behaviour in the lead
shielding that lines up with these regions - longitudinally: PbSh1_6,
Pb_Sh1_14, PbSh1_22 (see attachment please). The only common thing
between these lead regions and the beam spot regions where I see no
deposited energy or beam particle/photons is that they share the same
two planes as the boundaries in x (longitudinally). I have not done
anything special with these regions - physics-wise, thresholds, etc. I
see both neutron and photon fluences (using usrbin) in these lead
regions and the adjacent regions show deposited energies but not
these... This does not make any sense.

EMF-cut is set to 100 keV for e+, e- and 10 keV for photons.

I would like to know whether this is a bug in FLUKA or some silly
mistake from my part (which I can't seem to find).

Thanks and best wishes,

(image/png attachment: BP_in_BS_01_05_09_13.png)

(image/png attachment: BP_in_BS_02_06_10_14.png)

(image/png attachment: BP_in_BS_03_07_11_15.png)

(image/png attachment: Ph_in_BS_01_05_09_13.png)

(image/png attachment: Ph_in_BS_02_06_10_14.png)

(image/png attachment: Ph_in_BS_03_07_11_15.png)

Received on Thu Aug 15 2013 - 23:18:02 CEST

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