Negative Kerma factors were found by njoy processing of Ra-224,225 with the kinematic limit. This occurred by energy imbalance for the (n,2n), (n,3n) and (n,4n) reactions on both isotopes.
K. Shibata took action to remove the drawbacks. At first, those neutron spectra, which were given with LF=9, were converted to tabular forms with LF=1. Then, energy balance was checked and the spectra were modified near the threshold energies.