This report details the analyses and related uncertainties in measuring longitudinal-stress-density paths in indirect laser-driven ramp equation-of-state (EOS) experiments [Smith et al., Nat. Astron. 2(6), 452-458 (2018); Smith et al., Nature 511(7509), 330-333 (2014); Fratanduono et al., Science 372(6546), 1063-1068 (2021); and Fratanduono et al., Phys. Rev. Lett. 124(1), 015701 (2020)]. Experiments were conducted at the National Ignition Facility (NIF) located at the Lawrence Livermore National Laboratory. The NIF can deliver up to 2 MJ of laser energy over 30 ns and provide the necessary laser power and control to ramp compress materials to TPa pressures (1 TPa = 10 × 106 atmospheres). These data provide low-temperature solid-state EOS data relevant to the extreme conditions found in the deep interiors of giant planets. In these experiments, multi-stepped samples with thicknesses in the range of 40-120 µm experience an initial shock compression followed by a time-dependent ramp compression to peak pressure. Interface velocity measurements from each thickness combine to place a constraint on the Lagrangian sound speed as a function of particle velocity, which in turn allows for the determination of a continuous stress-density path to high levels of compressibility. In this report, we present a detailed description of the experimental techniques and measurement uncertainties and describe how these uncertainties combine to place a final uncertainty in both stress and density. We address the effects of time-dependent deformation and the sensitivity of ramp EOS techniques to the onset of phase transformations.

The work presented herein develops a high-throughput ejecta source platform named HEFESTUS, the High Explosive First Ejecta Shock Test Source. The proposed design utilizes small high explosive charges (< 1g) for ease of use in experimental facilities. The platform will be used to elucidate the ejecta formation process and quantify ejecta production rates. We perform detailed continuum hydrodynamics simulations to highlight the feasibility of such a platform. We investigate the sensitivity to generate ejecta with platform geometry, mesh refinement, and materials' equations of state.

Lithium fluoride (LiF) is a unique crystal possessing the largest reported bandgap of any material and is predicted to remain transparent to visible light under stresses in excess of 1000 GPa. Dynamic compression experiments often utilize LiF as a window material to maintain stress on a sample while enabling direct measurements of interface velocity. However, typical velocimetry diagnostics measure changes in the optical path length; therefore, an accurate understanding of LiF’s equation of state and refractive index is needed. Here, we present a measurement of the LiF refractive index up to 900 GPa from a low-temperature ramp-compression experiment at the National Ignition Facility. To demonstrate propagation of optical uncertainty from this work to equation of state measurements, simulations in which a tin–LiF interface reaches a peak stress of 825 GPa show that the principal isentrope of tin can be determined up to 1450 GPa with a 1.2% uncertainty in density while considering uncertainties in the optical response of LiF.

A model-independent technique was used to determine the $\gamma$-ray Strength Function ($\gamma$SF) of $^{56}$Fe down to $\gamma$-ray energies less than 1 MeV for the first time with GRETINA using the $(p,p')$ reaction at 16 MeV. No difference was observed in the energy dependence of the $\gamma$SF built on $2^{+}$ and $4^{+}$ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm(2)/s). The generator's maximum neutron flux at this irradiation position is 2.58 x 10(7) n/cm(2)/s +/- 5% (approximately 3 x 10(8) n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG.

A new code has been developed named RAINIER that simulates the γ-ray decay of discrete and quasi-continuum nuclear levels for a user-specified range of energy, angular momentum, and parity including a realistic treatment of level spacing and transition width fluctuations. A similar program, DICEBOX, uses the Monte Carlo method to simulate level and width fluctuations but is restricted in its initial level population algorithm. On the other hand, modern reaction codes such as TALYS and EMPIRE populate a wide range of states in the residual nucleus prior to γ-ray decay, but do not go beyond the use of deterministic functions and therefore neglect cascade fluctuations. This combination of capabilities allows RAINIER to be used to determine quasi-continuum properties through comparison with experimental data. Several examples are given that demonstrate how cascade fluctuations influence experimental high-resolution γ-ray spectra from reactions that populate a wide range of initial states.

Statistical γ -decay from highly excited states is determined by the nuclear level density (NLD) and the γ -ray strength function ( γ SF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and γ SF to evaluate the γ -width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers.

M.D. Jones, A.O. Macchiavelli, M. Wiedeking, L.A. Bernstein, H.L. Crawford, C.M. Campbell, R.M. Clark, M. Cromaz, P. Fallon, I.Y. Lee, M. Salathe, A. Wiens, ∗ A.D. Ayangeakaa, † D.L. Bleuel, S. Bottoni, ‡ M.P. Carpenter, H.M. Davids, § J. Elson, A. Görgen, M. Guttormsen, R.V.F. Janssens, ¶ J.E. Kinnison, L. Kirsch, A.C. Larsen, T. Lauritsen, W. Reviol, D.G. Sarantites, S. Siem, A.V. Voinov, and S. Zhu Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA iThemba LABS, P.O. Box 722, Somerset West 7129, South Africa Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94551, USA Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA Department of Physics, University of Oslo, N-0316 Oslo, Norway Department of Nuclear Engineering, University of California, Berkeley, California 94720, USA Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA A model-independent technique was used to determine the γ-ray Strength Function (γSF) of Fe down to γ-ray energies less than 1 MeV for the first time with GRETINA using the (p, p′) reaction at 16 MeV. No difference was observed in the energy dependence of the γSF built on 2 and 4 final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator designed for 40Ar/39Ar dating of geological materials produces nearly monoenergetic 2.45MeV neutrons at outputs of 108n/s. The narrow energy range is advantageous relative to the 235U fission spectrum neutrons due to (i) reduced 39Ar recoil energy, (ii) minimized production of interfering argon isotopes from K, Ca, and Cl, and (iii) reduced total activity for radiological safety and waste generation. Calculations provided show that future conditioning at higher currents and voltages will allow for a neutron output of over 1010n/s, which is a necessary requirement for production of measurable quantities of 39Ar through the reaction 39K(n,p)39Ar. A significant problem encountered with increasing deuteron current was beam-induced electron backstreaming. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics®. Experimental tests verified these simulations. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of -800V relative to the target.

A new measurement is presented of the 6Li(n,α)t cross section from 245 keV to 10 MeV using a 252Cf fission chamber with 6LiI(Eu) and Cs2LiYCl6:Ce (CLYC) scintillators which act as both target and detector. Neutron energies are determined from the time of flight (TOF) method using the signals from spontaneous fission and reaction product recoil. Simulations of neutron downscatter in the crystals and fission chamber bring 6Li(n,α)t cross section values measured with the 6LiI(Eu) into agreement with previous experiments and evaluations, except for two resonances at 4.2 and 6.5 MeV introduced by ENDF/B-VII.1. Suspected neutron transport modeling issues cause the cross section values obtained with CLYC to be discrepant above 2 MeV.

A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator design produces near monoenergetic 2.45 MeV neutrons at outputs of 10^8 n/s. Calculations provided show that future conditioning at higher currents and voltages will allow for a production rate over 10^10 n/s. A significant problem encountered was beam-induced electron backstreaming, that needed to be resolved to achieve meaningful beam currents. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics. Experimental tests verified these simulation results. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of -800 V relative to the target.

Background: The Cd isotopes are well studied, but experimental data for the rare isotopes are sparse. At energies above the Coulomb barrier, higher states become accessible.Purpose: Remeasure and supplement existing lifetimes and magnetic moments of low-lying states in $^{106}\mathrm{Cd}$.Methods: In an inverse kinematics reaction, a $^{106}\mathrm{Cd}$ beam impinging on a $^{12}\mathrm{C}$ target was used to Coulomb excite the projectiles. The high recoil velocities provide a unique opportunity to measure $g$ factors with the transient-field technique and to determine lifetimes from lineshapes by using the Doppler-shift-attenuation method. Large-scale shell-model calculations were carried out for $^{106}\mathrm{Cd}$.Results: The $g$ factors of the ${2}_{1}^{+}$ and ${4}_{1}^{+}$ states in $^{106}\mathrm{Cd}$ were measured to be $g({2}_{1}^{+})=+0.398(22)$ and $g({4}_{1}^{+})=+0.23(5)$. A lineshape analysis yielded lifetimes in disagreement with published values. The new results are $\ensuremath{\tau}(^{106}\mathrm{Cd};{2}_{1}^{+})=7.0(3)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ and $\ensuremath{\tau}(^{106}\mathrm{Cd};{4}_{1}^{+})=2.5(2)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$. The mean life $\ensuremath{\tau}(^{106}\mathrm{Cd};{2}_{2}^{+})=0.28(2)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ was determined from the fully-Doppler-shifted $\ensuremath{\gamma}$ line. Mean lives of $\ensuremath{\tau}(^{106}\mathrm{Cd};{4}_{3}^{+})=1.1(1)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ and $\ensuremath{\tau}(^{106}\mathrm{Cd};{3}_{1}^{\ensuremath{-}})=0.16(1)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ were determined for the first time.Conclusions: The newly measured $g({4}_{1}^{+})$ of $^{106}\mathrm{Cd}$ is found to be only 59% of the $g({2}_{1}^{+})$. This difference cannot be explained by either shell-model or collective-model calculations.

Background: The structure of the semimagic Sn-50 isotopes were previously studied via measurements of B(E2; 2(1)(+) -> 0(1)(+)) and g factors of 2(1)(+) states. The values of the B(E2; 2(1)(+)) in the isotopes below midshell at N = 66 show an enhancement in collectivity, contrary to predictions from shell-model calculations.Purpose: This work presents the first measurement of the 2(1)(+) and 4(1)(+) states' magnetic moments in the unstable neutron-deficient Sn-110. The g factors provide complementary structure information to the interpretation of the observed B(E2) values.Methods: The Sn-110 nuclei have been produced in inverse kinematics in an alpha-particle transfer reaction from C-12 to Cd-106 projectiles at 390, 400, and 410 MeV. The g factors have been measured with the transient field technique. Lifetimes have been determined from line shapes using the Doppler-shift attenuation method.Results: The g factors of the 2(1)(+) and 4(1)(+) states in Sn-110 are g(2(1)(+)) = +0.29(11) and g(4(1)(+)) = +0.05(14), respectively. In addition, the g(4(1)(+)) = +0.27(6) in Cd-106 has been measured for the first time. A line-shape analysis yielded tau(Sn-110;2(1)(+)) = 0.81(10) ps and a lifetime of tau(Sn-110;3(1)(-)) = 0.25(5) ps was calculated from the fully Doppler-shifted gamma line.Conclusions: No evidence has been found in Sn-110 that would require excitation of protons from the closed Z = 50 core.

The thermopower of W, Mo, Ta, Li and Sn has been measured relative to stainless steel, and the Seebeck coefficient of each of these materials has then been calculated. These are materials that are currently relevant to fusion research and form the backbone for different possible liquid limiter concepts including TEMHD concepts such as LiMIT. For molybdenum the Seebeck coefficient has a linear rise with temperature from SMo=3.9μVK−1 at 30°C to 7.5μVK−1 at 275°C, while tungsten has a linear rise from SW=1.0μVK−1 at 30°C to 6.4μVK−1 at 275°C, and tantalum has the lowest Seebeck coefficient of the solid metals studied with STa=−2.4μVK−1 at 30°C to −3.3μVK−1 at 275°C. The two liquid metals, Li and Sn have also been measured. The Seebeck coefficient for Li has been re-measured and agrees with past measurements. As seen with Li there are two distinct phases in Sn also corresponding to the solid and liquid phases of the metal. In its solid phase the SSn-solid=−1.5μVK−1 at 30°C and −2.5μVK−1 near the melting temperature of 231°C. There is a distinct increase in the Seebeck coefficient around the melting temperature as the Sn melts and stays relatively constant over the rest of the measured temperatures, SSn-melt=−1.4μVK−1 from 235°C to 275°C.

Three dimensional (3-D) virtual reality can be an effective tool for education, training and improved human performance in nuclear engineering applications. This technology can be used to model and simulate nuclear facilities with the help of custom-made packages and/or using well-known programming languages. We earlier reported the development of nuclear-specific virtual reality models using a well known game engine. This paper introduces some new features and scenarios which were developed for the models of interest. Specifically, some of the built-in features of the game engine are exploited to add nuclear-specific applications and to enhance interactivity. With this technology, Nuclear Power Plant (NPP) personnel and first responders can “play” and, hence, experience and emulate the operational and emergency scenarios of a plant through these specifically developed interactive and 3-D graphical models of nuclear facilities.