Neutron spectra from inertial confinement fusion targets for measurement of fuel areal density and charged particle stopping powers

Measurements of the ratio of dt to dd neutrons from pure deuterium fuel have been used as a method for determination of fuel areal density (〈ρR〉). The relationship between fuel 〈ρR〉 and dt neutron production becomes uncertain for 〈ρR〉 values large enough that the 1.01-MeV tritons from the d(d,t)p reaction lose a significant amount of energy in the fuel. A method based on neutron spectroscopy is described that improves the determination of fuel 〈ρR〉 in the region where tritons lose significant energy but have not yet thermalized. Charged particle stopping powers relevant to inertial confinement fusion ignition conditions may also be determined.