Author: Peter Gumplinger - TRIUMF, Vancouver, Canada
gum@t.nosp@m.rium.nosp@m.f.ca

This example demonstrates how ultra-cold neutrons (UCN) propagate in a guide pipe and how this can be simulated in Geant4.

INTRODUCTION

This example exhibits the functionality of UCN physics

GEOMETRY

The geometry consists of a single hollow pipe (cylinder) placed in a world.

Default World Size: G4Box - 1m x 1m x 100m

The pipe wall is made of G4_Ni while the world and, hence, the inside of the pipe is made from G4_Galactic

The G4UCNMaterialPropertiesTable properties are:

  "REFLECTIVITY" = 1
  "DIFFUSION" = 0.1
  "FERMIPOT" = 252.0 neV
  "SPINFLIP"= 0.
  "LOSS" = 12.5e-5
  "LOSSCS" = 0.
  "ABSCS"= 4.49    // 1/v loss cross-section  at room temp.
  "SCATCS" = 18.5  // (incoherent) "elastic" scattering cross-section

The MicroRoughnessParameters are:

  Roughness correlation length w = 30nm
  Surface roughness b = 1nm
  # of angles theta_i in the look-up tables: 180
  # of energie bins in the look-up tables: 1000
  min. and max. values of theta_i: 0*degree and 90*degree
  min. and max values of Energy: 1neV and 1000neV
  # of angles theta_o in the look-up table calculation: 15
  # of angels phi_o   in the look-up table calculation: 15
  angular cut: 0.01*degree

The default step limits in the vacuum is 1mm and maxTime is 100s

The simulation is in a G4UniformGravityField

PHYSICS LIST

The ExUCNPhysicsList defines only

G4Neutron, G4Proton, G4Electron, G4AntiNeutrinoE, G4MuonPlus, G4MuonMinus and G4GenericIon

Through ExUCNExtraPhysics the following processes are instantiated:

and in ConstructUCN()

THE PRIMARY GENERATOR

The primary kinematic consists of a single ultra-colde neutron (uniform between 1neV and 100neV from the origin uniform into 4pi

A RUN is a set of events.

VISUALIZATION

The Visualization Manager is set in the main () (see ExUCN.cc) for interactive session. The initialisation of the drawing is done via the command

/control/execute vis.mac

TESTING

This example handles the program arguments in a new way. It can be run with the following optional arguments:

% ExUCN [-m macro ] [-u UIsession] [-t nThreads]

The -t option is available only in multi-threading mode and it allows the user to override the Geant4 default number of threads. The number of threads can be also set via G4FORCENUMBEROFTHREADS environment variable which has the top priority.

Execute ExUCN in 'batch' mode from macro files e.g.

% ExUCN -m ExUCN.in > ExUCN.out &

Execute ExUCN in 'interactive' mode with visualization e.g.

% ExUCN
Idle> type your commands, for example:
Idle> run/beamOn 1
...

HISTOGRAMS

no histograms for now