Transport thresholds for low-energy neutrons

How do I define transport thresholds for low-energy neutrons?

In order to kill all low-energy neutrons below the group transport boundary one should use LOW-BIAS with WHAT(1) set to 1, i.e., selecting the highest energy group as cut-off boundary (inclusive). If you want to select a even higher neutron cut-off PART-THR has to be used which will then also stop the low-energy neutron group transport.

no neutron transport below 20 MeV

LOW-BIAS 1.0 0.0 Reg1 Reg2

no neutron transport below 500.0 MeV