Dawn A. Shaughnessy

Radiochemical Determination of Inertial Confinement Fusion Capsule Compression at the National Ignition Facility

We describe a radiochemical measurement of the ratio of isotope concentrations produced in a gold hohlraum surrounding an Inertial Confinement Fusion capsule at the National Ignition Facility (NIF). We relate the ratio of the concentrations of (n,γ) and (n,2n) products in the gold hohlraum matrix to the down-scatter of neutrons in the compressed fuel and, consequently, to the fuels areal density. The observed ratio of the concentrations of (198m+g)Au and (196g)Au is a performance signature of ablator areal density and the fuel assembly confinement time. We identify the measurement of nuclear cross sections of astrophysical importance as a potential application of the neutrons generated at the NIF.

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.

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.

The Radiochemical Analysis of Gaseous Samples (RAGS) apparatus for nuclear diagnostics at the National Ignition Facility (invited).

Radiochemical diagnostic methods are currently under development for the National Ignition Facility (NIF). Samples in the gas-phase offer a direct method of collection by pumping out the large target chamber following a NIF shot and transporting the gas down-stream for further analysis. Ignition capsules will have a small amount (roughly 1015 atoms) of dopant added to the inner-most layers of the ablator shell. These elements will undergo nuclear activation from neutrons, deuterons, or alpha particles produced via the fusion process. For example, doping 124Xe and 127I in the shell will create activated xenon isotopes that can be correlated to the amount of fuel ρR and long-range mix in the capsule. We are building the Radiochemical Analysis of Gaseous Samples (RAGS) apparatus for collecting and analyzing activated gases produced via the ignition process. Following a shot, gases will be pumped out of the chamber and transported to a two-part system. The first part consists of a pre-filter that will remove particulates and other reactive gases. The second part is a cryogenic xenon collection station where xenon will be isolated, and will then either be removed for mass spectrometric analysis, or counted via gamma spectroscopy. Preliminary results from RAGS commissioning will be presented and future improvements to the apparatus will also be discussed.

Production and isolation of homologs of flerovium and element 115 at the Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrometry

New procedures have been developed to isolate no-carrier-added (NCA) radionuclides of the homologs and pseudo-homologs of flerovium (Hg, Sn) and element 115 (Sb), produced by 12–15xa0MeV proton irradiation of foil stacks with the tandem Van-de-Graaff accelerator at the Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrometry (CAMS) facility. The separation of 113Sn from natIn foil was performed with anion-exchange chromatography from hydrochloric and nitric acid matrices. A cation-exchange chromatography method based on hydrochloric and mixed hydrochloric/hydroiodic acids was used to separate 124Sb from natSn foil. A procedure using Eichrom TEVA resin was developed to separate 197Hg from Au foil. These results demonstrate the suitability of using the CAMS facility to produce NCA radioisotopes for studies of transactinide homologs.

Note: Radiochemical measurement of fuel and ablator areal densities in cryogenic implosions at the National Ignition Facility

A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the (198)Au/(196)Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.

Determination of gaseous fission product yields from 14 MeV neutron induced fission of 238U at the National Ignition Facility

We determined fission yields of xenon (133mXe, 135Xe, 135mXe, 137Xe, 138Xe, and 139Xe) resulting from 14xa0MeV neutron induced fission of depleted uranium at the National Ignition Facility. Measurements begin approximately 20xa0s after shot time, and yields have been determined for nuclides with half-lives as short as tens of seconds. We determined the relative independent yields of 133mXe, 135Xe, and 135mXe to significantly higher precision than previously reported. The relative fission yields of all nuclides are statistically indistinguishable from values reported by England and Rider (ENDF-349. LA-UR-94-3106, 1994), with exception of the cumulative yield of 139Xe. Considerable differences exist between our measured yields and the JEFF-3.1 database values.

First fission yield measurements at the National Ignition Facility: 14-MeV neutron fission of 238U

The use of the Solid Radiochemistry diagnostic platform at the National Ignition Facility (NIF) has allowed the development and implementation of the Target Option Activation Device assembly for fielding materials of interest inside the NIF chamber during high yield neutron shots. Preliminary studies with ultra-depleted uranium have allowed for the measurements of fission yields of 238U. Radiochemical procedures were utilized for the separation of fission and reaction products from the target material to provide higher sensitivity measurements. Cumulative fission mass-yields for 32 different isobars, 72xa0≤xa0Axa0≤xa0153, were measured from experiments fielded on two separate NIF shots.

Characterization of the homologs of flerovium with crown ether based extraction chromatography resins: studies in nitric acid

Eichrom’s Pb resin, a crown-ether-based extraction chromatography resin, was characterized for separation of the flerovium (Fl) homologs, Pb and Sn. Batch uptake of Pb(II) and Sn(IV) radionuclides was determined from an HNO3 matrix. Pb(II) was strongly retained on the resin at all HNO3 concentrations, while Sn(IV) showed no uptake. Extraction kinetics for Pb(II) were examined and show suitable uptake on the second time scale. Separation methods for the isolation of individual homologs, Pb(II) and Sn(IV), have been established using 2xa0mL pre-packed vacuum flow Pb resin columns.

Production and separation of carrier-free 7Be

A high-purity carrier-free (7)Be was efficiently isolated following proton bombardment of a lithium hydroxide-aluminum target. The separation of beryllium from lithium and aluminum was achieved through a hydrochloric acid elution system utilizing cation exchange chromatography. The beryllium recovery, +99%, was assessed through gamma spectroscopy while the chemical purity was established by mass spectrometry. The decontamination factors of beryllium from lithium and aluminum were determined to be 6900 and 300, respectively.