title: Neutron activation diagnostics at the National Ignition Facility (invited).
abstract: 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 (115)In(n,n')(115 m) In reaction. Outside the chamber, zirconium and copper are used to measure 14 MeV deuterium-tritium fusion neutrons via (90)Zr(n,2n), (63)Cu(n,2n), and (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.
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA. bleuel1@llnl.gov
authors.forename: D L
authors.initials: DL
authors.lastname: Bleuel
authors.forename: C B
authors.initials: CB
authors.lastname: Yeamans
authors.forename: L A
authors.initials: LA
authors.lastname: Bernstein
authors.forename: R M
authors.initials: RM
authors.lastname: Bionta
authors.forename: J A
authors.initials: JA
authors.lastname: Caggiano
authors.forename: D T
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authors.lastname: Casey
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authors.lastname: Cooper
authors.forename: O B
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authors.lastname: Drury
authors.forename: J A
authors.initials: JA
authors.lastname: Frenje
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authors.initials: CA
authors.lastname: Hagmann
authors.forename: R
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authors.lastname: Hatarik
authors.forename: J P
authors.initials: JP
authors.lastname: Knauer
authors.forename: M Gatu
authors.initials: MG
authors.lastname: Johnson
authors.forename: K M
authors.initials: KM
authors.lastname: Knittel
authors.forename: R J
authors.initials: RJ
authors.lastname: Leeper
authors.forename: J M
authors.initials: JM
authors.lastname: McNaney
authors.forename: M
authors.initials: M
authors.lastname: Moran
authors.forename: C L
authors.initials: CL
authors.lastname: Ruiz
authors.forename: D H G
authors.initials: DH
authors.lastname: Schneider