RE: biasing in 800 MeV electron accelerator shielding

From: Joachim Vollaire <joachim.vollaire_at_cern.ch>
Date: Tue, 18 Jun 2013 21:16:08 +0000

Dear Yuanjie

Using the LAM-BIAS card is a first good approach, you do not indicate the parameters you used,
but reducing the interaction length for photonuclear interaction by a factor of
the order of 0.02 / 0.05 would be appropriate for this type of problem.


Concerning biasing to compensate the absorption of particles, the
most straightforward approach is region based importance biasing. You can make you walls as
concentric layers (using RPP / cylinders.... depending on your tunnel shape) and play with the importance ratio to keep the
population of tracked particles constant through the shielding. A good approach is to consider the attenuation length
of neutrons to define the thickness of the layers and importance ratio between adjacent regions. Note that in FLUKA importances can
only take values between 0.00001 and 100000.
If your geometry is too complicated to split you could use the USIMBS routine to obtain a similar results during particle tracking
without changing the geometry.

Then, there is one thing to consider, is your problem ~symmetrical (can you approximate your tunnel by a cylinder ?) ? If this is
the case then using the cylindrical binning and plotting a 2D r,z plot you will see that the results are satisfying as the scoring
volumes get larger as you penetrate the shielding.

Hoping this help
Best regards
Joachim

-----Original Message-----
From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-discuss_at_mi.infn.it] On
Behalf Of ???
Sent: 18 June 2013 09:58
To: fluka-discuss
Subject: biasing in 800 MeV electron accelerator shielding


Dear FLUKA user,

I want to simulate the neutron and photon dose rate after 50 cm concrete and 300
  cm soil shielding in a 800 MeV electron accelerator. The photonuclear reactions
  were activated and LAM-BIAS is used. Since it is a deep penetration problem, th
e biasing should be used. But I am not clear about what kind of biasing is prefe
rred in such a problem. Could someone give me some suggestion?
Many thanks!

Best wishes
Yuanjie
Received on Thu Jun 20 2013 - 11:10:18 CEST

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