Background: Neutron flux density is an important parameter related to nuclear power of the reactor. Digitized processing of neutron flux density in a wide measurement range of fission chamber detector has more advantages than the traditional analog circuits. Purpose: The aim is to improve the accuracy of neutron counting in the pulse mode

as well as mean square value calculation in the Campbell mode. Methods: The waveform of the output signal of fission chamber with various electronic noise was simulated

and then a trapezoidal shape filtering and digital adaptive filtering were employed to deal with digitized waveform signal of fission chamber in both low neutron flux density (pulse mode) and high neutron flux density (Campbell mode) circumstances. Results: By using these two methods

the accuracy of both the pulse counting and mean square value calculation was improved. Conclusion: Trapezoidal shape filtering and digital adaptive filtering can be applied to process digitized fission chamber output signal to achieve precise measurement of the neutron flux density in a wide range. Abstract