Mass measurements of exotic nuclei at the ESR

We plan to measure masses of exotic nuclei far from the valley of β-stability using the Experimental Storage Ring (ESR) at GSI, Darmstadt, as a time-of-flight (TOF), multi-turn mass spectrometer. For this purpose the ring must be tuned to an isochronous mode, so that the flight time per turn of an ion depends only on its mass-to-charge ratio and not on its velocity spread. For these measurements the timing detector is planned to be placed directly in the ESR to record each circulating ion.     

Shear viscosity of nuclear matter

This paper reports my recent studyIll on the shear viscosity of neutron-rich nuclear matter from a relaxation time approach. An isospin- and momentum-dependent interaction is used in the study. Dependence of density, temperature, and isospin asymmetry of nuclear matter on its shear viscosity have been discussed. Similar to the symmetry energy, the symmetry shear viscosity is defined and its density and temperature dependence are studied.     

Constraints on the skewness coefficient of symmetric nuclear matter within the nonlinear relativistic mean field model

Within the nonlinear relativistic mean field(NLRMF) model, we show that both the pressure of symmetric nuclear matter at supra-saturation densities and the maximum mass of neutron stars are sensitive to the skewness coefficient, J_0, of symmetric nuclear matter. Using experimental constraints on the pressure of symmetric nuclear matter at supra-saturation densities from flow data in heavy-ion collisions and the astrophysical observation of a large mass neutron star PSR J0348+0432, with the former favoring a smaller J_0 while the latter favors a larger J_0, we extract a constraint of -494 MeV≤J_0≤-10 MeV based on the NL-RMF model. This constraint is compared with the results obtained in other analyses.     

Comparison of oxidation model predictions with gasification data of IG-110, IG-430 and NBG-25 nuclear graphite

A phenomenological oxidation kinetics model of graphite is presented and its results are compared with the reported experimental gasification data for nuclear graphite of IG-110, IG-430 and NBG-25. The model uses four elementary chemical kinetics reactions, employs Gaussian-like distributions of the specific activation energies for adsorption of oxygen and desorption of CO gas, and accounts for the changes in the effective surface areas of free active sites and stable oxide complexes with weight loss. The distributions of the specific activation energies for adsorption and desorption, the values of the pre-exponential rate coefficients for the four elementary chemical reactions and the surface area of free active sites are obtained from the reported measurements using a multi-parameter optimization algorithm. At high temperatures, when gasification is diffusion limited, the model calculates the diffusion velocity of oxygen in the boundary layer using a semi-empirical correlation developed for air flows at Reynolds numbers ranging from 0.001 to 100. The model also accounts for the changes in the external surface area, the oxygen pressure in the bulk gas mixture and the effective diffusion coefficient in the boundary layer with weight loss. The model results of the total gasification rate and weight loss with time in the experiments agree well with the reported measurements for the three types of nuclear graphite investigated, at temperatures from 723 to 1226 K and weight loss fractions up to ～0.86.     

Semi-empirical predictions of even atomic energy levels and their hyperfine structure for the scandium atom

We report fine and hyperfine structure analysis of the system of even configurations of the Sc atom in a large multi-configuration basis. The complete energy scheme in the energy region up to about 50,000 cm⁻¹ has been established with the predicted values of the hyperfine structure constants A. The effects of the configuration interaction in the fine and hyperfine structure are discussed.     

Basic quantities of the equation of state in isospin asymmetric nuclear matter

Based on the Hugenholtz-Van Hove theorem,six basic quantities of the EoS in isospin asymmetric nuclear matter are expressed in terms of the nucleon kinetic energy t(k),the isospin symmetric and asymmetric parts of the single-nucleon potentials U0(ρ,k)and Usym,i(ρ,k).The six basic quantities include the quadratic symmetry energy Esym,2(ρ),the quartic symmetry energy Esym,4(ρ),their corresponding density slopes L2(ρ)and L4(ρ),and the incompressibility coefficients K2(ρ)and K4(ρ).By using four types of well-known effective nucleon-nucleon interaction models,namely the BGBD,MDI,Skyrme,and Gogny forces,the density-and isospin-dependent proper-ties of these basic quantities are systematically calculated and their values at the saturation density ρ0 are explicitly given.The contributions to these quantities from t(k),U0(ρ,k),and Usym,i(ρ,k)are also analyzed at the normal nuclear density ρ0.It is clearly shown that the first-order asymmetric term U/sym,1(ρ,k)(also known as the symmetry potential in the Lane potential)plays a vital role in deter-mining the density dependence of the quadratic symmetry energy Esym,2(ρ).It is also shown that the contributions from the high-order asymmetric parts of the single-nucleon potentials(Usym,i(ρ,k)with i＞1)cannot be neglected in the calculations of the other five basic quantities.Moreover,by analyzing the properties of asymmetric nuclear matter at the exact saturation density ρsat(δ),the corresponding quadratic incompressibility coefficient is found to have a simple empirical relation Ksat,2 = K2(ρ0)-4.14L2(ρ0).     

Constraining nuclear symmetry energy with the charge radii of mirror-pair nuclei

The nuclear charge radius plays a vital role in determining the equation of state of isospin asymmetric nuclear matter. Based on the correlation between the differences in charge radii of mirror-partner nuclei and the slope parameter(L) of symmetry energy at the nuclear saturation density, an analysis of the calibrated slope parameter L was performed in finite nuclei.In this study, relativistic and nonrelativistic energy density functionals were employed to constrain the nuclear symmetry energy ...     

Mechanical and leakrate predictions for nuclear power plant containments in accidental conditions

In 1996, EDF decided to build a containment model at the scale 1:3, the Maquette echange vapeur/air (MAEVA) mock-up, in order to check and study the behavior of a prestressed concrete containment vessel without liner in terms of mechanical strength and leaktightness, for loadings corresponding to its design and beyond design conditions. In parallel to the construction and testing of the mock-up, predictive calculations of the mechanical and leaktightness behaviour of the mock-up were performed in the framework of a cost shared R&D action supported by the European Union, the Containment Evaluation under Severe Accidents (CESA) project. The strategy of EDF concerning the R&D performed on leaktightness of concrete and concrete structures is first explained and the goal of two interesting programs is shortly presented and discussed in the first part of the paper. Then, the emphasis is made on the predictive calculations performed on the MAEVA mock-up by means of finite elements (FE) calculations. A summary of the main achievements is then given and the interest of FE calculations is discussed for describing both the mechanical and leaktightness behaviour of a concrete structure as a function of crack development.     

Small specimen predictions of fracture toughness for nuclear pressure vessel steels

The use of fracture mechanics in the fracture-safe design and continued safe operation of nuclear reactor pressure vessels has provided an incentive for the development of small specimens for obtaining pertinent fracture toughness data. Small specimens are required for economic reasons when a large number of heats are involved and for space limitation reasons such as in surveillance programs. Several approaches to obtaining fracture toughness from small specimens by either direct measurements or indirect correlations and calculations are reviewed, and their merits and limitations are discussed. Emphasis is placed on techniques which have been developed to determine static and dynamic fracture toughness from surveillance-type specimens. Recently developed techniques for obtaining J-initiation values from a single test specimen and methods for estimating lower and upper shelf fracture toughness from tensile properties are also presented.     

Density isomer of nuclear matter in an equivalent mass approach

The equation of state of symmetric nuclear matter is studied with an equivalent mass model. The equivalent mass of a nucleon has been expanded to order 4 in density. We first determine the first-order expansion coefficient in the quantum hadron dynamics, then calculate the coefficients of the second to fourth order for the given binding energy and incompressibility at the normal nuclear saturation density. It is found that there appears a density isomeric state if the incompressibility is smaller than a critical value. The model dependence of the conclusion has also been checked by varying the first-order coefficient.     

Long-term predictions of ambient dose equivalent rates after the Fukushima Daiichi nuclear power plant accident

To analyze radiation protection strategies and rehabilitation programs in Fukushima, prediction models have been developed for ambient dose equivalent rate distributions within the 80 km-radius around the Fukushima Daiichi nuclear power plant. The prediction models characterized by ecological half-lives of radioactive caesium for land-use, enable Fukushima residents to obtain distribution maps of ambient dose equivalent rates after the Fukushima Daiichi nuclear power plant accident. Model parameters such as the ecological half-lives for the short-term component and the fractional distribution of short-term component were evaluated using ambient dose equivalent rates through car/vehicle-borne surveys. It was found that the ecological half-lives among land-use differ only slightly, whereas the fractional distributions of the short-term component are clearly dependent on land-use. In addition, uncertainties concerning predictions of ambient dose equivalent rates arising from variability in model parameters were assessed using Monte Carlo simulations. Long-term changes of ambient dose equivalent rates were predicted for different land-use areas. Distribution maps of ambient dose equivalent rates for the next 30 years after the accident, created by the prediction models are expected to be useful for follow-up of the radiological situation since they provide information on the space variation of the ambient dose equivalent rates in inhabited areas.     

Apparent softening of the symmetry energy with the inclusion of non-nucleonic components in nuclear matter

Apparent softening of the symmetry energy with the inclusion of hyperon and quark degrees of freedom is demonstrated by the fact that the phase transition causes the change of the interaction and the suppression of nucleon fractions. The demonstration is fulfilled in the relativistic mean-field model.     

Dynamic model of the formation of collective heterogeneous boiling nuclei

Following a discussion of the wettability of solids by liquids and the associated wetting angles, details are given on the wetting angle hysteresis. Moreover the phenomenon of boundary line creep is demonstrated; the anticipated boundary line creep rates in the order of 10⁻⁵ mm/sec are made responsible for the dynamic behaviour of boiling nuclei (waiting time effect and related phenomena).Probable shapes of boiling nuclei and their physico-chemical conditions are discussed. Finally, a statistical dynamic model is outlined. It describes the formation of heterogeneous boiling nuclei in a collective of latent boiling nuclei. On the basis of simple models, a quantitatively usable formulation is presented for the expected distribution functions for the boiling probability as a function of superheat, time, and system parameters. This simplified model of computation is evaluated numerically and the results are discussed with respect to the applicability to experimental data.Based on this computational model it should be possible to obtain preliminary insights into the physico-chemical phenomena which take place at the interface and which are relevant to boiling nuclei.