  We report a new scenario of time-of-flight (TOF) technique in which fast
neutrons and delayed gamma-ray signals were both recorded in a millisecond time
window in harsh environments induced by high-intensity lasers. The delayed
gamma signals, arriving far later than the original fast neutron and often
being ignored previously, were identified to be the results of radiative
captures of thermalized neutrons. The linear correlation between gamma photon
number and the fast neutron yield shows that these delayed gamma events can be
employed for neutron diagnosis. This method can reduce the detecting efficiency
dropping problem caused by prompt high-flux gamma radiation, and provides a new
way for neutron diagnosing in high-intensity laser-target interaction
experiments.
