//$Id: .README.txt 98745 2016-08-09 13:36:03Z gcosmo $

///\file "exoticphysics/phonon/.README.txt"
///\brief Example phonon README page

/*! \page Examplephonon Example phonon

\author Daniel Brandt - SLAC \n
 dbrandt@slac.stanford.edu

This example demonstrates how phonon propagation in cryogenic crystals
can be simulated in Geant4.

\section phonon_s1 INTRODUCTION

Phonon propagation is different from most other Geant4 propagation
simulations in a number of respects:

- Phonons are massless particles moving slower than the speed of light

- Phonon propagation and momentum vectors are not parallel

- Events isotropic in phonon-momentum space are not isotropic in real
 space.

This example will simulate the propagation of acoustic phonons through
a Germanium crystal, providing processes to simulate phonon scattering
of isotopic impurities, mode mixing between polarization states and
anharmonic downconversion (phonon splitting). As such it provides all
the physics required to realistically simulate phonon propagation in
cryogenically cold semiconductor crystals.

\section phonon_s2 GEOMETRY

In this example the geometry is a cylindrical Germanium crystal
centered at (0,0,0) with Almuninium end caps. Phonons absorbed in the
Al end caps are counted by the sensitive detector.

\section phonon_s3 PRIMARY EVENT

The primary event is a single phonon of energy 7.5 meV at the center of
the Ge crystal. The polarization type (fast transvere, slow transverse or
longitudinal) is determined randomly according to the density of states
in Germanium. The direction of propagation is than determined by by the
User Stacking Action class XPhononStackingAction.

\section phonon_s4 EXECUTION & OUTPUT

The executable must be run from within the source directory of the example
to ensure that it can find the path for crystal data files.
Alternatively the search path for the crystal maps can be set in the
setting the G4LATTICEDATA environment variable. If this variable does not
exist, it defaults to ./CrystalMaps.

Data files for each crystal material are stored in a named subdirectory
under $G4LATTICEDATA/, along with a config.txt file which specifies the
numerical constants for the lattice.  This example includes germanium [111]
in CrystalMaps/Ge/.

Upon execution, the vis.mac visualization macro will automatically be
executed. For the visualization to work, OpenGL support must be installed.
The macro will automatically generate a single Primary Event (7.5 meV phonon)
at the center of the crystal.

The trajectory colour will indicate the polarization state of the phonon:
- Longitudinal:    blue
- Fast Transverse: green
- Slow Transverse: red

A small circle will be drawn wherever a phonon is absorbed into the 
Aluminium. All events within the Aluminium are written into plain-text
space-sparated-value (ssv) files:

\subsection phonon_s4_sub1 timing.ssv

- COLUMN 1: Time phonon was absorbed in ns since start of run
- COLUMN 2: Energy of phonon absorbed

\subsection phonon_s4_sub2 tcaustic.ssv

- COLUMN 1: x-position of absobrtion in mm
- COLUMN 2: y-position of absobrtion in mm
- COLUMN 3: z-position of absobrtion in mm

Every time a phonon is simulated, the information is appended to timing.ssv
and caustic.ssv. If the files do not exist they will be created.

\section phonon_s5 TESTING

In order to test the example, it can be run as
\verbatim
./XGeBox run.in > test.out
\endverbatim

This will create a single primary event and then cause the example to
terminate automatically, with all screen output redirected to test.out.

If all went well, test.out should be identical to run.out provided with
this example. Also, the files caustic.ssv and timing.ssv should have been 
created and be identical to caustic.out and timing.out respectively.

After the first time the example runs, it will append to caustic.ssv and
timing.ssv. If the testing should be re-run, then caustic.ssv and timing.ssv
will have to be deleted.

*/
