Density diagnosis of fusion targets by neutron activation

A new density diagnostic was developed based on neutron activation of selected materials in the targets to circumvent the problem of higher material areal densities and low target emissivities. For a series of intermediate-density experiments performed at Shiva, the short-lived (2-min half-life) aluminum-28 was used which was formed in the target by the bombardment of silicon-28 with 14.1-MeV neutrons from the D-T reaction. This system rapidly collects a known fraction of the aluminum-28 formed, transports it to a shielded detector, and determines its radioactivity. This allows derivation by computer simulations of fuel densities for a number of different targets. In addition, a simplified model that provides an independent cross check on the computer analysis was developed