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Prototypes of several National Ignition Facility (NIF) neutron time-of-flight (nTOF) detectors have been built and tested on OMEGA. One group uses a plastic scintillator coupled with a microchannel plate (MCP) photomultiplier tube (PMT), either a single-stage (gain up to 103) MCP PMT and a two-stage (gain up to 106) MCP PMT. Two ultrafast scintillators—BC-422 and BC-422Q—were used. Another nTOF prototype is based on a synthetic diamond wafer produced by the chemical vapor deposition. The nTOF detectors were tested on DD (2.45 MeV) and DT (14.1 MeV) neutron-producing implosions on OMEGA. Based on the results of these tests, a set of nTOF detectors is proposed for use on the NIF to measure ion temperature and DD and DT neutron yields from 109 to 1019. [ABSTRACT FROM AUTHOR]

We characterize the response of chemical vapor deposition (CVD) diamond detectors to inertial confinement fusion (ICF) neutrons generated at the OMEGA laser fusion facility in Rochester, NY. Four detectors are tested: three utilizing "optical grade" CVD diamond, and one utilizing "electronic grade" CVD diamond. Using a 50 Ω measurement system, we find that the optical grade wafers, biased to 1000 V/mm, have an average sensitivity of 0.24 µV ns/n for 2.5 MeV (DD fusion) neutrons and 0.62 µV ns/n for 14.0 MeV (DT fusion) neutrons. At the same E field, the electronic grade wafer has a sensitivity of 0.56 and 1.43 µV ns/n for 2.5 and 14 MeV neutrons, respectively. Linear dynamic range for the optical grade material is shown to be at least 10[sup 5]. Average full width at half maximum response times, as measured with pulsed laser and 3 GHz scope, are 376 and 880 ps for optical and electronic grades, respectively. These characteristics make CVD diamond suitable for ICF applications such as neutron time-of-flight spectroscopy, bang time measurements, and ion temperature measurements. [ABSTRACT FROM AUTHOR]

A detector for fuel areal density measurements in inertial confinement fusion capsules has been designed. Observation of neutrons scattered in an imploded deuterium capsule (0.27-0.6 MeV) is a promising method for areal density measurements in the National Ignition Facility DD surrogate capsules. In order to detect scattered neutrons, we need to (1) suppress interference due to the strong direct neutron burst and (2) suppress the background produced by neutrons scattering on nontarget material (mainly from the target chamber). In our detector system, we suppress direct neutrons by gating the detector. We suppress the nontarget background neutrons by placing the detector outside the target chamber and limiting the view of the detector with collimators. In addition, we are developing a lithium-glass scintillation-fiber detector (LG-SCIFI) to detect the scattered neutrons. The LG-SCIFI will work as a multichannel scintillator array. The scintillation signal will be amplified by a microchannel plate image intensifier, which is gated to accept signals only in a specific time-of-flight window for the scattered neutrons. The gated scintillation image will be recorded by a charge-coupled device. Since the detector is segmented, neutron detection events will be clearly identified as bright spots in the gated image. [ABSTRACT FROM AUTHOR]

We examine various options for calibration of the National Ignition Facility neutron detectors in the energy range E<14 MeV. These options include: downscatter of D–T fusion neutrons using plastic targets; nuclear reactions at a Tandem Van de Graaf accelerator; and “white” neutrons from a pulsed spallation source. As an example of the pulsed spallation option, we present calibration data that was recently acquired with a single crystal chemical vapor deposition diamond detector at the Weapons Neutron Research Facility at Los Alamos National Laboratory. [ABSTRACT FROM AUTHOR]