Abstract
Abstract
Frequency gradient analysis (FGA) neutron-gamma pulse shape
discrimination (PSD) based on Fourier transform has proved to be an
effective method for discrimination between two types of pulses by
simply constructing a discrimination parameter by subtracting the
amplitude of the 1st frequency component from the 0th frequency
component. However, the discrimination parameter constructed by the
above method could not meet the requirements at some lower sample
rates, and the dark noise caused using optoelectronic devices such
as miniaturized SiPMs array further erodes the difference between
the two frequency components. This paper proposes a new
discrimination parameter construction method based on FGA for
neutron-gamma discrimination, which is referred as mFGA (modified
FGA). This discrimination parameter uses the 0th frequency component
and other frequency components to enhance the discrimination
performance. A neutron detector module consisting of a
25.4 mm× 25.4 mm× 50.8 mm
NaI:Tl,6Li (NaIL) scintillator and an array of 8 × 8
SiPMs was established to verify the method of mFGA. The module
measured a 252Cf neutron source under three shielding
conditions: no shield, 5 cm high-density polyethylene (HDPE), and
10 cm lead brick. The proposed mFGA method was used to calculate
the figure of merit (FoM) under each shielding condition and
compared to the traditional frequency gradient method (FGA) and the
traditional charge comparison method (CCM). The results show that
the discrimination performance with the mFGA method is significantly
improved. Taking the HDPE shielding group as an example, the
performances of the three methods are FoM-FGA =1.14,
FoM-mFGA =2.75, FoM-CCM =0.92. At the same time,
with the increase of energy, due to the neutron gamma pulse becoming
similar, and the discrimination performance of FGA and CCM decrease
significantly. The discrimination performance of the mFGA method is
relatively stable in all energy regions. Therefore, the proposed
method is superior to the traditional FGA of the 0th frequency minus
the 1st frequency and has a good application prospect for
neutron-gamma discrimination with detectors of poor signal quality.