first draft on stack

documentation/howto_create_module.rst

 Howto create new physics modules
 ================================
 
-There are different types of physics modules, which you can add to the CORSIKA~8 physics process 
+There are different types of physics modules, which you can add to the CORSIKA 8 physics process 
 sequence. Modules can act on particles, secondaries or the entire stack. Modules can create new particles 
 or they can modify or delete particles. They can also produce output. 
 
 Types of different modules are explained in ::modules
 
-When creating new modules, we suggest to stick as close as possible to the default CORSIKA~8 coding guidelines 
+When creating new modules, we suggest to stick as close as possible to the default CORSIKA 8 coding guidelines 
 and code structure. This makes code review and sharing with others not more complicated than needed. 
 
-When your modules creates output, use the available CORSIKA~8 output machinery. This is not explained here. 
+When your modules creates output, use the available CORSIKA 8 output machinery. This is not explained here. Also learn 
+how to use units, and use the loggers from the very beginning. Furthermore, get aquinted with C++17.  
 
 Let's consider the case of an "InteractionProcess" which will remove the projectile particle and create 
 secondary particles on the stack instead. It also has a cross section in order to evaulate the probability 
 with respect to other InteractionProcesses. Create a header file "SimpleProcess.hpp", which is conceptually
-based to resemble (roughly) a Matthews-Heitler model:
+based to resemble (roughly) a Matthew-Heitler model:
 
 .. code-block:: c++
 

documentation/index.rst

@@ -9,6 +9,7 @@ Welcome to the CORSIKA 8 air shower simulation framework.
    readme_link
    output
    particles
+   particle_stack
    media
    units
    environment

documentation/particles.rst

-Particle Properties
-===================
+Particle Storage and Stack
+==========================
 
-.. toctree::
-   particle_classes
+Particles in memory are stored in a Stack. The Stack handles the memory management and access to particle data
+properties. The stack can be extended with additional fields that then become part of the particle object.
 
-.. doxygengroup:: Particles
-   :project: CORSIKA8
-   :members:
+The standard Stack object in CORSIKA 8 is the NuclearStackExtension, further extended with internal 
+fields like `geometry node` and `weight` or `history`. But the important part is the `NuclearStackExtension`. 
 
+There are several ways to create particles:
+* novel particles on the stack:
+  *  stack::addParticle(particle_data_type const&)  
+  *  stack::addParticle(nuclear_particle_data_type const&)   
+  *  stack::addParticle(particle_data_momentum_type const&)  
+  *  stack::addParticle(nuclear_particle_data_momentum_type const&)  
+* secondary particles:
+  *  stack::addSecondary(parent const&, particle_data_type const&)  
+  *  stack::addSecondary(parent const&, nuclear_particle_data_type const&)   
+  *  stack::addSecondary(parent const&, particle_data_momentum_type const&)  
+  *  stack::addSecondary(parent const&, nuclear_particle_data_momentum_type const&)  
+  or directly:
+  *  particle::addSecondary(particle_data_type const&)  
+  *  particle::addSecondary(nuclear_particle_data_type const&)   
+  *  particle::addSecondary(particle_data_momentum_type const&)  
+  *  particle::addSecondary(nuclear_particle_data_momentum_type const&)  
+
+The content of these method parameters are:
+
+*  particle_data_type: {PID [corsika::Code], kinetic energy [HEPEnergyType], direction [DirectionVector], position [Point], time[TimeType]}
+*  particle_data_momentum_type: {PID [corsika::Code], momentum [MomentumVector], position [Point], time[TimeType]}
+*  nuclear_particle_data_type: {PID [corsika::Code], kinetic energy [HEPEnergyType], direction [DirectionVector], position [Point], time[TimeType], A [unsigned int], Z [unsigned int]}
+*  nuclear_particle_data_momentum_type: {PID [corsika::Code], momentum [MomentumVector], position [Point], time[TimeType], A [unsigned int], Z [unsigned int]}
 
-