Three-dimensional simulation strategy to determine the effects of turbulent mixing on inertial-confinement-fusion capsule performance.

In this paper, we present and justify an effective strategy for performing three-dimensional (3D) inertial-confinement-fusion (ICF) capsule simulations. We have evaluated a frequently used strategy in which two-dimensional (2D) simulations are rotated to 3D once sufficient relevant 2D flow physics has been captured and fine resolution requirements can be restricted to relatively small regions. This addresses situations typical of ICF capsules which are otherwise prohibitively intensive computationally. We tested this approach for our previously reported fully 3D simulations of laser-driven reshock experiments where we can use the available 3D data as reference. Our studies indicate that simulations that begin as purely 2D lead to significant underprediction of mixing and turbulent kinetic energy production at later time when compared to the fully 3D simulations. If, however, additional suitable nonuniform perturbations are applied at the time of rotation to 3D, we show that one can obtain good agreement with the purely 3D simulation data, as measured by vorticity distributions as well as integrated mixing and turbulent kinetic energy measurements. Next, we present results of simulations of a simple OMEGA-type ICF capsule using the developed strategy. These simulations are in good agreement with available experimental data and suggest that the dominant mechanism for yield degradation in ICF implosions is hydrodynamic instability growth seeded by long-wavelength surface defects. This effect is compounded by drive asymmetries and amplified by repeated shock interactions with an increasingly distorted shell, which results in further yield reduction. Our simulations are performed with and without drive asymmetries in order to compare the importance of these effects to those of surface defects; our simulations indicate that long-wavelength surface defects degrade yield by approximately 60% and short-wavelength drive asymmetry degrades yield by a further 30%.

Comparison of three methods for determining CT dose profile: presenting the tritium method.

The purpose of the present work was to describe a method of using an imaging plate from a computed radiography system to determine the computed tomography (CT) dose profile (the tritium method) and to compare this method with point-dose measurements using a solid-state detector (CT Dose Profiler; RTI Electronics, Mölndal, Sweden) and the indirect method of comparing the air kerma-length product (P(KL)) at different beam collimations. The three methods were used to determine the full width at half maximum (FWHM) of the dose profile of a multi-slice CT at different nominal beam collimations. For all beam collimations, the obtained deviation between the tritium method and the CT Dose Profiler was smaller than 0.1 mm. The maximum relative error was 2 %. For the P(KL) method, the deviation from the CT Dose Profiler was between 0.2 and 0.4 mm, resulting in a relative error larger than 10 % for the smallest beam collimation even after normalisation to a known FWHM. In conclusion, the proposed method of using an imaging plate to determine the FWHM of the CT dose profile has a high accuracy and shows good agreement with the more advanced method of point-dose measurements using a solid-state detector.

Internal dose assessments: uncertainty studies and update of ideas guidelines and databases within CONRAD project.

The work of Task Group 5.1 (uncertainty studies and revision of IDEAS guidelines) and Task Group 5.5 (update of IDEAS databases) of the CONRAD project is described. Scattering factor (SF) values (i.e. measurement uncertainties) have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Based upon this work and other published values, default SF values are suggested. Uncertainty studies have been carried out using both a Bayesian approach as well as a frequentist (classical) approach. The IDEAS guidelines have been revised in areas relating to the evaluation of an effective AMAD, guidance is given on evaluating wound cases with the NCRP wound model and suggestions made on the number and type of measurements required for dose assessment.

Tritiation of lysozyme by the free-radical interceptor method and determination of the tritium distribution among individual residues of the chromatographically homogeneous protein.

Lysozyme has been tritiated by the free-radical interceptor method, which involves reaction of the carbon free radicals, resulting from gamma-irradiation of the lyophilized protein in a vacuum, with tritiated hydrogen sulfide. This technique resulted in a high yield of tritiated enzyme which was chromatographically indistinguishable from the native protein. To characterize this material with respect to its tritium distribution, it was first reduced, carboxymethylated, and digested with chymotrypsin. The peptides were separated and purified by ion exchange chromatography and electrophoresis and then analyzed to determine the specific activities of 78 of the 129 residues in the protein chain. The tritium was found to be broadly distributed, with only 12 residues apparently devoid of label. The relative specific activity, defined as the ratio of the specific activity of a given residue to the average specific activity for all residues of the same kind within the protein, did not exceed the value of 3.73 for isoleucine at position 88. A distinct spatial relationship is seen among the more heavily labeled residues when these results are related to the x-ray diffraction model of lysozyme. Thus, residues 16, 18, 19, 21, 23, 29, 31, and 32 may be grouped with 105, 110, 113, and 115; these highly labeled residues are close to a strongly hydrophobic region. Another heavily labeled area involves residues 50, 54, 57. 83, 84, and 88. In addition, residues 1 and 6 at the amino end of the chain are heavily labeled, as are 118, 121, and possibly 119 at the carboxyl end. This distribution of tritium appears to reflect the secondary free-radical distribution in the irradiated protein. These observations confirm previous indications that the secondary distribution is influenced by the conformation of the protein molecule.