The first direct measurement of fuel density-radius product $\rho R$ in laser-fusion experiments is obtained by measuring the number of deuterium and tritium ions elastically scattered out of the fuel by 14-MeV fusion neutrons. They were recorded with the solid-state track detector CR-39. The energy spectrum of these particles is found to agree well with the theoretical result. This diagnostic was used in low- and high-compression experiments and gave measured $\rho R$ values of 1.3×${10}^{-4\mathrm{}}$ and 1.2×${10}^{-3\mathrm{}}$ g/${\mathrm{cm}}^2$, with an uncertainty of ∼ 20%.

• Received 3 May 1982

DOI:https://doi.org/10.1103/PhysRevLett.49.463