AbstractA multi-foil activation method is applied to neutron measurement in the Gekko XII laser inertial fusion experiment. The total neutron yield is determined by using several threshold activation detectors, where the practical efficiencies have been estimated with a Monte Carlo neutron transport calculation in a detailed model of the experimental assembly. The neutron spectra over a wide energy range are also determined through their adjustment techniques using the multi-foil activation data. In particular, the new application to the fuel areal density (〈pR〉) measurement based on this method is introduced and is discussed on the expected measurement accuracy.