Background:In the nuclear disarmament process

the measurement and verification of uranium casting in sealed container are important to process control and treaty implementation.It is a difficult and hot problem to verify uranium casting in a sealed metal container

due to the weak intensity of neutron and γ rays of uranium.Purpose:We want to measure the correlation functions of different casting in uranium casting verifications.Methods:Two BC501 scintillation detectors are placed outside the tagged neutron cone and in opposite position.The α detector forms the first channel pulse signal

while the two BC501 scintillation detectors form the second and third channel pulse signals.Those three pulsed time series are recorded by high speed acquisition system.The correlation functions between these signals are calculated by the time series.Results:Putting the two BC501 detectors into the tagged neutron cone

the time of flight for the 14-MeV neutron is measured.The FWHM in TOF spectrum is 2.0 ns.Putting the two BC501 detectors outside the tagged neutron cone

the correlation functions measured by high speed acquisition system and MCA are consistent.The spontaneous neutron decay constants of the castings are measured byγ rays.The decay constant of 6.5-kg Pb component is 184 μs 1.The decay constants of 4-kg and 15-kg HEU casting are 210 μs 1and 128 μs 1

respectively.The correlation functions C12(τ)

C13(τ) and C23(τ) are acquired.In C12(τ)

the γray peak coming from the inelastic reaction of 14-MeV neutrons with the casting is 5.0 ns before the neutron peak of fission chain.This time difference can estimate the casting position in container.The integrations of the C12(τ)

C13(τ)and C23(τ) increase with the casting mass.The C23(τ) values of Pb component and DU casting are far less than the values of HEU casting.The C23(τ) integration of Pb component is 3.0% comparing with 15-kg HEU casting

while the integration of 4-kg HEU is 24.8%.The C23(τ) can demonstrate reliably the existence of HEU casting.The C12(τ) and C13(τ) values between HEU and DU casting with similar mass are different obviously.Conclusions:The spontaneous neutron decay constants of the components are stable

it can be used as an important parameter independently for the uranium casting verification.The correlation function C23(τ) is effective to judge the existence of uranium casting.By use of the integrations of the C12(τ)

C13(τ) and C23(τ)

the mass or enrichment of the uranium casting can be distinguished.