Running the MCNPX input file: ex1, should give you a file called: wssa Look for "Source Surface Write" in the manual. If you rename this file to: rssa and run the script called:, that should run McStas using as source the rssa file. This will create a file called wssa, which you can rename to rssa and run the MCNPX input file: ex1_read. There are no tallies (detectors) in this file, this you will need to define yourself. It is meant as an example to show you how the procedure is done. I hope it help -if not, please ask PS: I realize that the renaming of files is annoying - but it was never quite annoying enough for me to fix it... best regards, Esben