Neutron yields are measured at the National Ignition Facility (NIF) by an extensive suite of neutron activation diagnostics. Neutrons interact with materials whose reaction cross sections threshold just below the fusion neutron production energy, providing an accurate measure of primary unscattered neutrons without contribution from lower-energy scattered neutrons. Indium samples are mounted on diagnostic instrument manipulators in the NIF target chamber, 25-50 cm from the source, to measure 2.45 MeV deuterium-deuterium fusion neutrons through the {sup 115}In(n,n'){sup 115m} In reaction. Outside the chamber, zirconium and copper are used to measure 14 MeV deuterium-tritium fusion neutrons via {sup 90}Zr(n,2n), {sup 63}Cu(n,2n), and {sup 65}Cu(n,2n) reactions. An array of 16 zirconium samples are located on port covers around the chamber to measure relative yield anisotropies, providing a global map of fuel areal density variation. Neutron yields are routinely measured with activation to an accuracy of 7% and are in excellent agreement both with each other and with neutron time-of-flight and magnetic recoil spectrometer measurements. Relative areal density anisotropies can be measured to a precision of less than 3%. These measurements reveal apparent bulk fuel velocities as high as 200 km/s in addition to large areal density variations between the pole and equator of the compressed fuel.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2011

Nuclear Physics using NIF

The National Ignition Facility (NIF) is the world's premier inertial confinement fusion facility designed to achieve sustained thermonuclear burn (ignition) through the compression of hydrogen isotopic fuels to densities in excess of 10{sup 3} g/cm{sup 3} and temperatures in excess of 100 MK. These plasma conditions are very similar to those found in the cores of Asymptotic Giant Branch (AGB) stars where the s-process takes place, but with a neutron fluence per year 10{sup 4} times greater than a star. These conditions make NIF an excellent laboratory to measure s-process (n,{gamma}) cross sections in a stellar-like plasma for the first time. Starting in Fall 2009, NIF has been operating regularly with 2-4 shots being performed weekly. These experiments have allowed the first in situ calibration of the detectors and diagnostics needed to measure neutron capture, including solid debris collection and prompt {gamma}-ray detection. In this paper I will describe the NIF facility and capsule environment and present two approaches for measuring s-process neutron capture cross sections using NIF.

08 HYDROGEN↗