Relevant changes in PENELOPE 2014
---------------------------------

The formats of the input and geometry files of the 2014 version are
compatible with those of version 2011; however, material data files are
organized differently and need to be generated with the 2014 version of
the 'material.f' program (you can also use the program 'tables.f').

Essentially, the physics and the structure of the code are the same as
those of version 2011. The programming style has been slightly improved
by replacing some common blocks by modules (i.e., we use Fortran 90).
Note that 'penelope.f', 'pengeom.f', and 'penvared.f' should be compiled
in this order and before the main program, to make the modules available
to those program units that use them.

The main differences with the previous version 2011 of PENELOPE are the
following:

1) Global parameters (maximum number of materials, dimension of the
energy interpolation grid, size of the secondary stack) are defined in
module 'PENELOPE_mod'.

2) Particle state variables are stored in module 'TRACK_mod', which is
used in the main program and in the tracking routines.

3) Ionizations of inner shells by electron and positron impact are
described as proper inelastic collisions. This ensures that the net
deposited energy in each interaction event is positive.

4) Cross sections for ionization of N subshells calculated from the
relativistic distorted wave Born approximation have been included in the
database.

5) For electrons and positrons, the energy loss DESOFT due to soft
interactions between two consecutive hard interactions (which is
delivered through module 'PENELOPE_mod'), can be deposited uniformly
along the step. That is, instead of depositing DESOFT at the hinge we
can use a kind of continuous-slowing-down model, and provide a more
realistic description of the slowing down due to energy-loss events.
This feature is used in 'penmain.f' to evaluate the average energy loss
along track segments that end at interfaces, thus giving improved
stability for geometries involving thin bodies. It also reduces the
dependence of results on the value of the user parameter DSMAX. Manifest
improvements are found, e.g., in the case of electron transport through
a stack of very thin foils.

6) The geometry package 'pengeom.f' has been modified. Array dimensions
are now defined in the module 'PENGEOM_mod'. Element labels have been
extended to 4-character alphanumeric strings.

7) The variance-reduction routines 'penvared.f' have been reformulated.
The new routines include the techniques of bremsstrahlung splitting, and
Woodcock delta scattering of photons. X-ray slitting can also be applied
in 'penmain.f'.

8) The program 'penmain.f' includes additional options (bremsstrahlung
and x-ray splitting, modifiable geometry parameters), as well as a
refined calculation of absorbed dose in inhomogeneous volumes.

9) Two programs, 'penmain-sum.f' and 'pencyl-sum.f', are provided for
combining results from independent simulation runs of the same problem
(poor man's parallelisation).

10) Optionally, the program 'penmain.f' can keep track of the age of
particles, measured from the start of the primary particle that
initiates each shower.

