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Title: Studies of Background Levels for the NIF Yield Diagnostics from Neutron and Gamma Radiation

Abstract

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is nearing completion of construction and is preparing for the National Ignition Campaign (NIC) with potentially significant yield in 2010. The design of a wide range of yield diagnostics in and outside the target-bay of the NIF must consider scattered background neutrons and neutron-induced gamma rays to measure neutrons and x-rays from target. The large and complex target chamber and facility make the calculation of scattered neutrons and gamma rays extremely challenging. The NIF was designed with shielded locations for many of the yield diagnostics including the neutron alcove and four diagnostic mezzanines. Accurate calculation of the background levels in these shielded locations requires advanced Monte Carlo techniques, e.g., variance reduction. Placement, size, and materials of collimators on the line of sight (LOS) through the shielding must be evaluated to trade off signal levels and unwanted backgrounds. The background at these locations is also affected by neutrons that pass through the laser beam tubes and scatter off of structures and walls in the switch yards. Detailed 3D Monte Carlo analyses are performed to determine neutron and gamma fluxes for some of the yield diagnostics.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
922121
Report Number(s):
UCRL-CONF-234392
TRN: US200803%%249
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: IFSA 2007, Kobe, Japan, Sep 09 - Sep 14, 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; COLLIMATORS; CONSTRUCTION; DESIGN; GAMMA RADIATION; IGNITION; LASERS; LAWRENCE LIVERMORE NATIONAL LABORATORY; NEUTRONS; SHIELDING; TARGET CHAMBERS; US NATIONAL IGNITION FACILITY

Citation Formats

Song, P, Eder, D, Moran, M, Landen, O, O'Brien, D, and Hsing, W. Studies of Background Levels for the NIF Yield Diagnostics from Neutron and Gamma Radiation. United States: N. p., 2007. Web.
Song, P, Eder, D, Moran, M, Landen, O, O'Brien, D, & Hsing, W. Studies of Background Levels for the NIF Yield Diagnostics from Neutron and Gamma Radiation. United States.
Song, P, Eder, D, Moran, M, Landen, O, O'Brien, D, and Hsing, W. Mon . "Studies of Background Levels for the NIF Yield Diagnostics from Neutron and Gamma Radiation". United States. doi:. https://www.osti.gov/servlets/purl/922121.
@article{osti_922121,
title = {Studies of Background Levels for the NIF Yield Diagnostics from Neutron and Gamma Radiation},
author = {Song, P and Eder, D and Moran, M and Landen, O and O'Brien, D and Hsing, W},
abstractNote = {The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is nearing completion of construction and is preparing for the National Ignition Campaign (NIC) with potentially significant yield in 2010. The design of a wide range of yield diagnostics in and outside the target-bay of the NIF must consider scattered background neutrons and neutron-induced gamma rays to measure neutrons and x-rays from target. The large and complex target chamber and facility make the calculation of scattered neutrons and gamma rays extremely challenging. The NIF was designed with shielded locations for many of the yield diagnostics including the neutron alcove and four diagnostic mezzanines. Accurate calculation of the background levels in these shielded locations requires advanced Monte Carlo techniques, e.g., variance reduction. Placement, size, and materials of collimators on the line of sight (LOS) through the shielding must be evaluated to trade off signal levels and unwanted backgrounds. The background at these locations is also affected by neutrons that pass through the laser beam tubes and scatter off of structures and walls in the switch yards. Detailed 3D Monte Carlo analyses are performed to determine neutron and gamma fluxes for some of the yield diagnostics.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Aug 27 00:00:00 EDT 2007},
month = {Mon Aug 27 00:00:00 EDT 2007}
}

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  • One of the planned core neutron diagnostics for NIF will use material activation to aid in determining information about target neutron yields. While this technique was routinely used on Nova and is in use today on Omega, the substantially larger chamber size and neutron yields for NIF raise several new issues for this technique. The effect of neutron scattering, due to the larger amount of entrant equipment inside the chamber, and more importantly, scattering inside the NIF target itself, is shown to be a significant effect. The appropriate location of the counting room to analyze activated samples that is sufficientlymore » protected from neutron fluences is discussed. There are no significant safety issues related to sample handling when using In and Cu for short durations (minutes). We recommend placement and thickness of Cu samples based on neutron yield.« less
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