  A novel algorithm for the discrimination of neutron and {\gamma}-ray with
wavelet transform modulus maximum (WTMM) in an organic scintillation has been
investigated. Voltage pulses arising from a BC501A organic liquid scintillation
detector in a mixed radiation field have been recorded with a fast digital
sampling oscilloscope. The performances of most pulse shape discrimination
methods in scintillation detection systems using time-domain features of the
pulses are affected intensively by noise. However, the WTMM method using
frequency-domain features exhibits a strong insensitivity to noise and can be
used to discriminate neutron and {\gamma}-ray events based on their different
asymptotic decay trend between the positive modulus maximum curve and the
negative modulus maximum curve in the scale-space plane. This technique has
been verified by the corresponding mixed-field data assessed by the
time-of-flight (TOF) method and the frequency gradient analysis (FGA) method.
It is shown that the characterization of neutron and gamma achieved by the
discrimination method based on WTMM is consistent with that afforded by TOF and
better than FGA. Moreover, because the WTMM method is it self presented to
eliminate the noise, there is no need to make any pretreatment for the pulses.
