Gabriele Cosmo
79 lines
2.6 KiB
Markdown
79 lines
2.6 KiB
Markdown
\page ExampleGB03 Example GB03
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## Geometry based biasing
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This example illustrates a use of generic biasing classes to implement a
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technique near to "geometry importance biasing".
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The geometry is the same than in EM tests, with the sampling calorimeter
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made of a series of layers of absorber and gap.
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The biasing applies to neutrons only.
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Instead of explicitly assigning "importance" values to the layers, we
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split neutrons moving forward and kill the ones moving backward, when they
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reach the exit of an absorber volume.
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The splitting factor can be controlled by command line, eg:
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```
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/GB03/biasing/setSplittingFactor 2
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```
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which also determines the killing probability : 1/(splitting factor).
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It can be seen than when defining 10 layers (see exampleGB03.in), a
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splitting factor 2 works fine : we don't suffer from under- or over-splitting.
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If going to 20 layers, then a splitting with a factor 2 is too large,
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and the biasing suffers from over-splitting. (And we can not go lower than
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"2", which would mean "1" and hence, no biasing...)
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To alleviate the over-splitting, we introduce a probability to apply the
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splitting (and killing) (this is one solution, others can be considered), that
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can be changed as:
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```
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/GB03/biasing/setApplyProbability 0.5
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```
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With above value, we can see that we recover a satisfactory biasing scheme,
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with neutrons penetrating the entire setup, without over-splitting.
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The commands in ```/GB03/biasing``` section are available only if application
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started with biasing "on".
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The classes involved are:
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- GB03BOptnSplitOrKillOnBoundary : which is the biasing operation making
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the splitting and killing;
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- GB03BOptrGeometryBasedBiasing : which is the biasing operator, making
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decision to use above operation, and configuring it, passing it the
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splitting factor and probability to apply the biasing.
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## HOW TO START ?
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The example can be executed in "batch" mode if macro file name is specified
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or interactive mode.
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To run it:
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```
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./exampleGB03 [-m macro_file] [-b [on|off]]
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```
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Without parameters the application runs in interactive mode with biasing "on".
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## THE OUTPUT
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During the run the histograms of energy distributions for neutrons and gammas
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after the "shield" volume and their positions along x axis are filed and
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saved to GB03.root file.
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Depending on ```/GB03/verbose``` flag
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For *verbose >= 1* all particles penetrating the shield were counted and
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printed with their weights and Emin Emax values.
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The track #, particle, kinetic energy and position on each step are printed
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if *verbose >= 2*.
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The particle count per thread is also printed if *verbose >= 3*.
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