Radiochemical Diagnostics Research Articles

Radiochemical diagnostics at the National Ignition Facility.

Since the National Ignition Facility (NIF) was commissioned in 2009, radiochemical techniques have been viewed as a potential method for diagnosing the performance of an NIF fusion shot. Radiochemical methods can also be used in conjunction with NIF shots to measure nuclear reaction cross sections in regimes that are inaccessible at accelerator facilities and can provide a route to produce radioactive tracer materials that can be used for other applications. This review presents the current status of radiochemical diagnostics at the NIF. Experimental results and the status of both solid and gaseous debris collection radiochemistry are presented.

Solid debris collection for radiochemical diagnostics at the National Ignition Facility

Radiochemical analysis of post-ignition debris inside the National Ignition Facility (NIF) target chamber can help determine various diagnostic parameters associated with the implosion efficiency of the fusion capsule. This technique is limited by the ability to distinguish ablator material from other debris and by the collection efficiency of the capsule debris after implosion. Prior to designing an on-line collection system, the chemical nature and distribution of the debris inside the chamber must be determined. The focus of our current work has been on evaluating capture of activated Au hohlraum debris on passive foils (5 cm diameter, 50 cm from target center) post-shot. Preliminary data suggest that debris distribution is locally heterogeneous along the equatorial and polar line-of-sights.

Overview of the 2009 Release of the Evaluated Nuclear Data Library (ENDL2009)

The Lawrence Livermore National Laboratory (LLNL) Physics Division has produced the next iteration of LLNL's evaluated nuclear database, ENDL2009. ENDL2009 is the second in a series of major ENDL library releases designed to support LLNL's current and future nuclear data needs. This library includes 585 distinct transport-ready evaluations in the neutron sub-library and many physics improvements for stockpile stewardship, attribution signatures, key radiochemical diagnostics and performance of conventional and hybrid fission/fusion reactors. In building this library, we adopted the best of the world's nuclear data efforts: 46% of the library is from the ENDF/B-VII.0 library, 10% is from the JENDL libraries and 8% from other libraries. The remaining 36% of the neutron sub-library and all of the charged-particle sub-libraries consist of new evaluations developed at LLNL for the ENDL2009 library. In addition, ENDL2009 supports new features such as energy-dependent Q values from fission, support for unresolved resonances and average momentum deposition. Finally, this release is our most highly tested release as we have strengthened our already rigorous testing regime by adding tests against LANL Activation Ratio Measurements and more than 1200 new critical assemblies. Our testing is now being incorporated into our development process and is serving to guide database improvements.

Prompt radiochemistry at the National Ignition Facility (invited)

Understanding mix in inertial confinement fusion (ICF) experiments at the National Ignition Facility requires the diagnosis of charged-particle reactions within an imploded target. Radiochemical diagnostics of these reactions are currently under study by scientists at Los Alamos and Lawrence Livermore National Laboratories. Measurement of these reactions requires assay of activated debris and tracer gases from the target. Presented below is an overview of the prompt radiochemistry diagnostic development efforts, including a discussion of the reactions of interest as well as the progress being made to collect and count activated material.

PROMPT BETA SPECTROSCOPY AS A DIAGNOSTIC FOR MIX IN IGNITED NIF CAPSULES

The National Ignition Facility (NIF) technology is designed to drive deuterium–tritium (DT) internal confinement fusion (ICF) targets to ignition using indirect radiation from laser beam energy captured in a hohlraum. Hydrodynamical instabilities at interfaces in the ICF capsule leading to mix between the DT fuel and the ablator shell material are of fundamental physical interest and can affect the performance characteristics of the capsule. Here we describe new radiochemical diagnostics for mix processes in ICF capsules with plastic or Be (0.9% Cu ) ablator shells. Reactions of high-energy tritons with shell material produce high-energy β-emitters. We show that mix between the DT fuel and the shell material enhances high-energy prompt beta emission from these reactions by more than an order of magnitude over that expected in the absence of mix. We further show how a mix signal could be detectable in an ignition failure regime corresponding to yields greater than about 2 kJ.

Investigation of the radiative strength function

The radiative strength function (RSF) is key for understanding nuclear reaction rates in areas ranging from astrophysics to radiochemical diagnostics. The RSF also provides a tool for understanding the characteristics of gamma-ray cascades. Unresolved transitions in nuclear deexcitation processes are best described by statistical properties such as the radiative strength function. The sequential extraction method developed at the Oslo Cyclotron Laboratory provides data for radiative strength functions for gamma-ray energies from 1MeV to the neutron binding energy. The data are averaged over about 100keV energy bin and normalized to the average total radiative width of neutron resonances. The radiative strength functions in all nuclei studied show a characteristic increase with increasing gamma-ray energy. However, the detailed structures in the radiative strength function for various nuclei show different behavior in various mass regions. In rare-earth nuclei, a resonance structure near 3MeV is observed. For several lighter nuclei (A<100), a large enhancement for low transition energies is observed. This unexpected phenomenon is not explained by existing theoretical models. Additional investigations using independent measurements are underway. The experiments and analysis methods will be described briefly. Experimental data for Fe, Sn, and Yb will be shown to illustrate the variety of behavior observed for the radiative strength function.