Measurement of the ⁸⁹Y(n,2n)⁸⁸Y and ⁸⁸Y(n,2n)⁸⁷Y Cross Sections Using Radiochemically Doped Target Capsules at the National Ignition Facility

The National Ignition Facility (NIF) is an Inertial Confinement Fusion (ICF) research facility at Lawrence Livermore National Laboratory (LLNL). During an ICF shot, a high-density carbon (HDC) capsule filled with deuterium and tritium (DT) is compressed to extreme densities and temperatures with 192 high energy laser beams. The resulting DT fusion produces alpha particles and a significant yield (≤10¹⁸) of 14.1 MeV neutrons in a short pulse (~100 ps). Material on the inside of the target capsule sees extremely large neutron fluxes (10^27-33 n/s/cm²), allowing (n,2n) cross section measurements to be made with low amounts of target material (~10¹³ atoms). The short burn time of a NIF shot also opens the possibility of reactions on excited nuclear states with lifetimes longer than the NIF burn. In an effort to begin measuring (n,2n) cross sections at NIF, radiochemical techniques were developed to add material to the inner surface of NIF capsules. Initial experiments measured the ⁸⁹Y(n,2n)⁸⁸Y cross section in a cryo-layered DT implosion with target capsules doped with ⁸⁹Y, ¹⁶⁹Tm, and ¹⁵²Eu. The results from two shots demonstrated the method is effective as the known cross section value was reproduced. Two shots with capsules containing ⁸⁸Y and ¹⁶⁹Tm were fired in January and September 2025 to measure the ⁸⁸Y(n,2n)⁸⁷Y cross section. The results from the NIF experiments to measure the ⁸⁹Y(n,2n)⁸⁸Y and ⁸⁸Y(n,2n)⁸⁷Y cross sections will be presented.