  Neutron shielding simulations by using GEANT4 and PHITS code are performed.
As a neutron source, $^{252}$Cf is considered and the energy distribution of
the neutrons emitted from $^{252}$Cf is assumed the Watt fission spectrum. The
neutron dose equivalent rates with and without the shield are estimated for
shielding materials such as graphite, iron, polyethylene, NS-4-FR and
KRAFTON-HB. For the neutron shielding simulations by using GEANT4, high
precision (G4HP) model with G4NDL 4.2 based on ENDF-VII data are used. And for
PHITS simulations, JENDL-4.0 library are used for the same purpose. It is found
that differences between the shielding calculations by using GEANT4 with G4NDL
4.2 and PHITS with JENDL-4.0 library are not significant for all cases
considered in this work. We investigate the accuracy of the neutron dose
equivalent rates obtained from GEANT4 and PHITS by comparing our simulation
results with experimental data and other values calculated earlier. Calculated
neutron dose equivalent rates agree well with the experimental dose equivalent
rates within 20% errors except for polyethylene. For polyethylene material,
discrepancy between the calculations and the experiments are up to 40% but all
simulations show consistent features.
