Livermore plutonium array program: experiments and calculations

The first precision array measurements with high-density plutonium-metal cylindrical parts of 3 and 6 kg took place at the Livermore Critical Assembly Facility from 1965 to 1969. Cubic arrays of up to sixty-four 6-kg parts were measured. Mock high-explosive epoxy moderators were used in several measurements. Experiments observing the effects of simulated body reflectors provided personnel safety guidance for the construction of these arrays. A comparison of Monte Carlo calculations and the experimental measurements indicated that the calculational method is sufficiently accurate to be used in nuclear safety guidance for arrays of these elements. Included for comparison are calculations for arrays comprised solely of the plutonium parts. Also included are calculations for 6-kt-part arrays in which a 0.479-cm-wide gap at the midplane has been eliminated and where the spacing was varied for each idealized array