Use of 41Ar production to measure ablator areal density in NIF beryllium implosions.

For the first time, ⁴¹Ar produced by the (n,Y) reaction trom ⁴⁰Ar in the beryllium shell ot a DT filled Inertial Confinement Fusion capsule has been measured. ⁴¹Ar is co-deposited with beryllium in the sputter deposition ot the capsule shell. Combined with a measurement ot the neutron yield, the radioactive ⁴¹Ar then quantifies the areal density of beryllium during the DT neutron production. The measured 1.15 ± 0.17 × 10⁺⁸ atoms of ⁴¹Ar are 2.5 times that from the best post-shot calculation, suggesting that the ⁴¹Ar and Be areal densities are correspondingly higher than those calculated. Possible explanations are that (1) the beryllium shell is compressed more than calculated, (2) beryllium has mixed into the cold DT ice, or more likely (3) less beryllium is ablated than calculated. Since only one DT filled beryllium capsule has been fielded at NIF, these results can be confirmed and expanded in the future. [ABSTRACT FROM AUTHOR]