Void swelling in MA956 ODS steel irradiated with 122 MeV Ne-ions at elevated temperatures

An investigation of a commercial oxide dispersion-strengthened steel (MA9561) irradiated with high energy Ne-ions to high doses at elevated temperatures is presented. Specimens of MA956 oxide dispersion strengthened steel together with a 9% Cr ferritic/martensitic steel, e.g., Grade 92 steel were irradiated simultaneously with 20Ne-ions (with 122 MeV) to successively increasing damage levels of 1, 5 and 10 dpa at the damage peak at 440 C and 570 C, respectively. Cross-sectional microstructures of the specimens were investigated with transmission electron microscopy. MA956 oxide dispersion strengthened steel showed a higher resistance to void swelling especially to void growth at the grain boundaries than the ferritic/martensitic steel, e.g., Grade 92 steel did, and thus exhibited a prominence for an application in the situation of a high He production at high temperatures. The suppression of the growth of voids especially at the grain boundaries in MA956 is ascribed to an enhanced recombination of the point defects and a trapping of Ne atoms at the interfaces of the yttrium–aluminum oxide particles and the matrix.

Circumstantial Evidence for a Soft Nuclear Symmetry Energy at Suprasaturation Densities

Within an isospin- and momentum-dependent hadronic transport model, it is shown that the recent FOPI data on the pi(-)/pi(+) ratio in central heavy-ion collisions at SIS/GSI energies [Willy Reisdorf , Nucl. Phys. A 781, 459 (2007)] provide circumstantial evidence suggesting a rather soft nuclear symmetry energy E-sym(rho) at rho >= 2 rho(0) compared to the Akmal-Pandharipande-Ravenhall prediction. Some astrophysical implications and the need for further experimental confirmations are discussed.

Triton-He-3 relative and differential flows as probes of the nuclear symmetry energy at supra-saturation densities

Using a transport model coupled with a phase-space coalescence afterburner, we study the triton-He-3 (t-He-3) ratio with both relative and differential transverse flows in semicentral Sn-132 + Sn-124 reactions at a beam energy of 400 MeV/nucleon. The neutron-proton ratios with relative and differential flows are also discussed as a reference. We find that similar to the neutron-proton pairs, the t-He-3 pairs also carry interesting information regarding the density dependence of the nuclear symmetry energy. Moreover, the nuclear symmetry energy affects more strongly the t-He-3 relative and differential flows than the pi(-)/pi(+) ratio in the same reaction. The t-He-3 relative flow can be used as a particularly powerful probe of the high-density behavior of the nuclear symmetry energy.