collisions in particle systems

Dear all, I am new to this forum and to Blender
I have recently started using this great sw for the creation or realistic 3D geometry of sand grains. I have created a closed box and an emitter of little spheres.
I can accurately simulate the collisions with the walls and many other interesting things but these spheres are always intersecting each other. I can include a force field to let them feel a repulsive force between them but it is not enough.
Is there a way to include hard collisions between all the emitted particles?

For real physical interaction between the particles use the game engine. There are many discussions about this so using the forum search may be useful

thank you!
It’s becoming a little bit more complicated because I have to first create grains with the particle system and then switch to the game engine but the results are great!

Anyone know if the Bullet Integration will include that (outside of BGE), self collisions or particles and/or particle instances or if we have to wait for the node based system Lucas is working on before even dreaming of such things?