Dear @hanhechong,
Thank you for your question.
As to what regards the produced neutron, this is rather straightforward. Please find here a user routine
mgdraw.f (5.5 KB) which scores every neutron interaction. This is too much for what you need, so you can additionally filter on ICODE.EQ.100 and/or 101 just for the produced neutrons, but I kept this way to discuss with you the vanishing part of the question.
Could you elaborate a it more on what you mean by vanishing? The neutrons could fall below transport threshold (if you put a higher one than default), or be absorbed in a nuclear interaction.
Please note that you would have to compile this routine by linking with ldpmqmd, since you are also requesting COALESCE above 125 MeV/n. COALESCE slides, no. 19.
I have adjusted your input file without the first OPEN and SOURCE cards.
Best,
Daniel