Gamma rays interacting mainly with the counter wall
produce small pulses which are registered in the low energy
end of the pulse height distributions. Helium nuclei scattered
at wide angles as well as the recoil nuclei of the other gases
present in the detectors, also contributes to this part of the
distributions. The gamma ray contribution to the pulse
height distribution of 3
He counter can extend almost up to
the thermal neutron peak [10]. Under normal operating
conditions neutrons and gamma rays are effectively distinguished
from each other by rise time discrimination, since,
typically, pulses originating from gamma rays have longer
rise times [9]. Spectra collected using gamma and beta rays
show similar behavior in both detectors. They contribute to
the low energy end of the pulse height distribution with the
count number exponentially decreasing as channel number
increases. Data collected with various shaping time constants
were very well fitted (R2499:95%) with the function