  Pressurized helium-4 based fast neutron scintillation detector offers an
useful alternative to organic liquid-based scintillator due to its relatively
low response to the $\gamma$-rays compared to the latter type of scintillator.
In the present work, we have investigated the capabilities of a pressurized
$^4$He (PHe) detector for the detection of fast neutrons in a mixed radiation
field where both the neutrons and the $\gamma$-rays are present. Discrimination
between neutrons and $\gamma$-rays is achieved by using fast-slow charge
integration method. We have also conducted systematic studies of the
attenuation of fast neutrons and $\gamma$-rays by high-density polyethylene
(HDPE). These studies are further corroborated by simulation analyses conducted
using GEANT4, which show qualitative agreement with the experimental results.
Additionally, the simulation provides detailed insights into the interactions
of the radiation quanta with the PHe detector. Estimates of the scintillation
signal yield are made based on our GEANT4 simulation results by considering the
scintillation mechanism in the PHe gas.
