1. An apparatus for absolute nuclear material assay, comprising: a multigate neutron multiplicity counter, a processor that time dependent moments, a processor that fits dead time, lifetime, biases, and selects the number of parameters to solve for, a processor that iteratively solves algebra for 5 parameters and biases, a processor that compares truncated data moments with untruncated and truncated theoretical moments, and a processor that checks parameter consistency and stability by adjusting the number of unknowns.