To modify the beam you can read in the user guide on the general particle source.
To check for particles exiting the volume, you need to introduce another check into the stepping action, I believe it is touched in another thread on the forum.
To modify the beam you can read in the user guide on the general particle source.
To check for particles exiting the volume, you need to introduce another check into the stepping action, I believe it is touched in another thread on the forum.