Note: Radiochemical measurement of fuel and ablator areal densities in cryogenic implosions at the National Ignition Facility.

A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the (198)Au/(196)Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.

Radiochemical determination of Inertial Confinement Fusion capsule compression at the National Ignition Facility.

We describe a radiochemical measurement of the ratio of isotope concentrations produced in a gold hohlraum surrounding an Inertial Confinement Fusion capsule at the National Ignition Facility (NIF). We relate the ratio of the concentrations of (n,γ) and (n,2n) products in the gold hohlraum matrix to the down-scatter of neutrons in the compressed fuel and, consequently, to the fuel's areal density. The observed ratio of the concentrations of (198m+g)Au and (196g)Au is a performance signature of ablator areal density and the fuel assembly confinement time. We identify the measurement of nuclear cross sections of astrophysical importance as a potential application of the neutrons generated at the NIF.

Pre-concentration and measurement of low levels of gamma-ray emitting radioisotopes in coastal waters.

We describe extensive testing of a large-volume, high-speed water sampler for the concentration and measurement of radionuclides using high-resolution gamma ray spectrometry. The sampler processed hundreds to thousands of liters of natural waters with variable suspended sediment and salinity loads at flow rates of 10-201/min. Extraction of most radionuclides in the water column was accomplished through the combination of physical filtration down to 0.1 microm particle size and chemical separation of dissolved species on cellulose-based inorganic sorbent beds without recourse to complex, or hazardous chemistry. Performance and extraction efficiencies for suites of radioisotopes were determined in the laboratory and in the field with river and coastal ocean water samples. Extraction and recovery efficiencies are better than 90% for most fission and activation product radioisotopes. This methodology has broad application to the study of the distribution and fate of radioisotopes in coastal waterways.