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Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a body-centered cubic (bcc) crystal structure. Ion irradiation is an indispensable tool in the study of the radiation effects of materials for nuclear energy systems. Due to the shallow damage depth in ion-irradiated materials, the nanoindentation test is the most commonly used method for characterizing the changes in mechanical properties after ion irradiation. Issues that affect the analysis of irradiation hardening may arise due to changes in the surface morphology and mechanical properties, as well as the inherent complexities in nanoscale indentation. These issues, including changes in surface roughness, carbon contamination, the pile-up effect, and the indentation size effect, with corresponding measures, were reviewed. Modeling using the crystal plasticity finite element method of the nanoindentation of ion-irradiated materials was also reviewed. The challenges in extending the nanoindentation test to high temperatures and to multiscale simulation were addressed. [ABSTRACT FROM AUTHOR]

BackgroundThe triple-to-double coincidence ratio-Čerenkov (TDCR-Čerenkov) method can be applied to the activity measurement of radionuclides by detecting the Čerenkov photons produced in a non-scintillation solution. The computation of the detection efficiency of this method is based on the premise that the energy of emitted β is completely deposited in the solution. However, this precondition is ideal and does not apply to the actual measurement because of the counting loss caused by the restrictions of a finite solution and the wall of the counting vial (i.e., wall effect).PurposeThis study aims to analyze the influence of the wall effect on the computation of detection efficiency.MethodsThe transport process of emitted β from the solution to the vial wall was analyzed in sections. Thereby the relationship between the number of Čerenkov photons and the deposition energy spectra of emitted β with different energies in different matrices was obtained. This relationship was used to further improve the calculation model of the TDCR-Čerenkov method. Subsequently, the calculation model was simplified to reduce the required time. Geant4 calculated the deposition spectra of emitted β in different matrices, subsequently, the efficiency of different nuclides was calculated using curves of the number of Čerenkov photons vs. the energy of the emitted β. To verify the accuracy of the improved calculation model, measurements were carried out on a variety of pure β-emitters.ResultsThe results derived from the improved TDCR-Čerenkov method are in good agreement with those of the TDCR-LS method. Especially for high energy β-emitters, the relative deviation of the results between the TDCR-Čerenkov and TDCR-LS methods is reduced from 0.47% for the original method to 0.02% (90Y), and 0.64% to -0.16% (32P).ConclusionsThe TDCR-Čerenkov method is more accurate when considering the wall effect in the activity measurement of high-energy β-emitters.

Background55Fe is a low-energy radionuclide that is difficult to measure and decays to a ground state of 55Mn through pure electron capture (EC), accompanied by the emission of Auger electrons and low-energy X-ray. As iron is the main component of nuclear reactor building materials, significant amounts of 55Fe have been produced in nuclear reactors and other neutron-producing nuclear facilities.PurposeThis study aims to develop an 55Fe nuclide standard through the absolute measurement of 55Fe activity and provides activity traceability services for 55Fe measuring instruments to ensure the accuracy and consistency of the measurement results of calibration instruments.MethodsThe liquid scintillation triple-to-double coincidence ratio (TDCR) method was applied to determining the activity of 55Fe. First, based on nuclear and atomic data of 55Fe, the electron deposition spectrum of 55Fe in a scintillator was calculated using a random atomic rearrangement model. Second, the counting efficiency of single-energy electron was computed based on the free parameter model. The total efficiency curve of 55Fe was then obtained by summing the efficiency of all deposited electrons. Finally, the experimental counting efficiency was derived by measuring the TDCR value and combining it with the total efficiency curve to realize an absolute measurement of 55Fe activity.ResultsThe experimental results show that correction factors for the asymmetric effect of photomultiplier tube (PMT) quantum efficiency obtained on test samples are between 1.001 and 1.005. The measured specific activity of 55Fe is 94.15 kBq∙g-1 with a relative standard uncertainty of 0.45%. Experimental efficiency is better than 63% for double coincidence logic sum of liquid scintillation counter.ConclusionsThis study demonstrates that low relative standard uncertainty of 55Fe activity could be achieved using the liquid scintillation TDCR method with high detection efficiency, and more consistent measurement results can be obtained after applying the asymmetry correction of PMT quantum efficiency.

Fluffy spherical structure NiCo2S4 decorated with cubic phase hexagonal nanosheets was successfully synthesized through a two-step solvothermal method for energy storage. The electrochemical measurements reveal its good reversibility together with its high rate ability (1354 F g−1 at 0.5 A g−1 and 1128 F g−1 at 10 A g−1). Positron annihilation techniques (positron annihilation lifetime spectra and Doppler broadening spectra) were conducted to investigate the defects and the electronic structure of the two-step synthesized NiCo2S4. The results showed high S/W ratio, which is consistent with the electrochemical results. An asymmetric supercapacitor (ASC) was assembled in a button cell using the two-step synthesized NiCo2S4 as the positive electrode material and commercially activated carbon as the negative electrode material. The ASC presents a high energy density of 30.8 W kg−1 at a power density of 352.2 W kg−1 and 15.5 W kg−1 at a power density of 6860 W kg−1, with excellent cycling stability (89.3% capacitance retention after 3000 cycles) and nearly 100% Coulombic efficiency. [ABSTRACT FROM AUTHOR]

Influence of the ion irradiation at elevated temperatures on the novel preceramic paper-derived SiCf/SiC laminated composites fabricated by spark plasma sintering was investigated. The composites were subjected to high-dose simultaneous irradiation of silicon (Si) ions at 400 °C. Irradiation induces amorphization of the damaged area up to 30 dpa, and then recrystallization of amorphous regions with increasing dose occur. No evidence of cavities was found in SiCf/SiC composites irradiated by silicon ions up to 100 dpa. The irradiated composites pre-injected with 5000 appm He displays low swelling (~ 0.3%). The irradiation with Si ions may suppress the cavity nucleation and they growth in SiC layers. [ABSTRACT FROM AUTHOR]