SIMULATION OF RADIATION BACKGROUNDS ASSOCIATED WITH NUCLEAR DIAGNOSTICS IN THE NATIONAL IGNITION FACILITY
Experiments resulting in a significant neutron yield are scheduled to start in 2010 at the National Ignition Facility (NIF). Several experiments utilizing Tritium-Hydrogen-Deuterium (THD) and Deuterium-Tritium (DT) targets are scheduled as part of the National Ignition Campaign (NIC). A wide range of diagnostics will be used to measure several parameters of implosion such as the core and fuel shape, temperatures and densities, and neutron yield. Accurate evaluations of the neutron and gamma backgrounds are important for several diagnostics, such as the High Energy X-ray Imager (HEXRI) and Neutron-Time-Of-Flight (nTOF). Several sources of neutron and gamma backgrounds will impact the accuracy of the diagnostics measurements. Fusion neutrons generated by fuel burn and secondary neutrons resulting from the fusion neutrons interaction with structures present inside and outside the Target Chamber (TC) contribute to the neutron background. In the meantime, X-rays emitted from the implosion, X-rays resulting from Laser Plasma Interaction (LPI) of NIF beams with the hohlraum, and gamma-rays induced by neutron interactions with different structures inside and outside the TC contribute to the gamma background. A detailed model has been developed of the NIF facility and all structures inside the TC. Several Monte-Carlo simulations were performed to identify the expected signal-to- background ratios at several potential locations for the HEXRI and nTOF diagnostics. Gamma backgrounds associated with HEXRI were significantly reduced by using a tungsten collimator. The collimator resulted in the reduction of the gamma background at the HEXRI scintillator by more than an order of magnitude during the first 40 ns following a THD shot. The nTOF20 detectors inside the Neutron Spectrometry room are exposed to low levels of neutron and gamma background during yield shots.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 967291
- Report Number(s):
- LLNL-CONF-416019; TRN: US0904342
- Resource Relation:
- Conference: Presented at: The 6th International Conference on Inertial Fusion Sciences and Applications 2009, San Francisco, CA, United States, Sep 06 - Sep 11, 2009
- Country of Publication:
- United States
- Language:
- English
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