ABSTRACT
The titanium-stabilized austenitic stainless steel Fe-15Cr-15Ni, which shows enhanced resistance to irradiation swelling compared with more traditional 316Ti, has been selected as a core material for fast reactors. Data on the evolution of irradiation swelling in 15-15Ti steels at very high doses, which cannot be easily achieved by neutron irradiation, are still lacking. In this paper, the swelling behavior of the titanium-modified austenitic stainless steel 15-15Ti was investigated by pre-implantation of He at room temperature followed by Ni-ion irradiation at 580 °C to peak doses of 120, 240 and 400 dpa. Relatively small cavities were observed in the zone of helium implantation, while large cavities appeared in the region near the damage peak. A correction formula for the dpa curve was proposed and applied to samples with large swelling. It was found that the steady-state swelling rate of 15-15Ti remains at ~1%/dpa even at high doses. By comparing the swelling data of the helium-implanted and helium-free regions at same doses, 70 dpa and 122 dpa, the suppression of swelling by excessive helium can be deduced at such doses.
ABSTRACT
The accuracy of activity determination for activated nuclide 56Mn is the key to the manganese bath method applying to the characterization of radionuclide neutron source. As an alternative to the 4π(C)-γ method, TDCR-Cerenkov method could also be applied to the measurement of 56Mn in the manganese bath device, if the existing calculation model is extended. There are two difficulties when the existing TDCR-Cerenkov method is applied to the activity determination of 56Mn. One is that the efficiency computation of gamma transitions, and the other is the interference contributed by Cerenkov photons emitted in the photomultiplier windows induced by Compton scattering. In this study, the above two difficulties are solved by extending the calculation model. For efficiency computation, the decay scheme of 56Mn is taken into account in the calculation of efficiency. Among them, the efficiency of gamma transition is calculated from the simulated secondary electronic spectra. In addition, Cerenkov photons emitted in photomultiplier windows are corrected by additional light proof experiment and improved calculation model. The results derived from this extended method are in good agreement with other standardization technique.
ABSTRACT
Using Monte Carlo simulation and experiment, this study shows that the self-attenuation correction factors (SACFs) for identical samples measured with different detectors are not equal. The Geant4 toolkit is used to study and the following conclusions are drawn: compared with the unattenuated case, when γ-rays with different energies are attenuated by the matrix and container, the distribution of γ-rays on the surface of the entrance window of the detector is distorted. As a consequence, the SACF should be modified to account for both the self-attenuation of the sample, and the corresponding changes in detector efficiency as a result of the changes in the spatial distribution and to the energy spectra caused by the self-attenuation of the source matrix. This paper demonstrates that within certain energy ranges, and for a certain range of detectors, the required SACF modifications are not negligible. Detector parameters should therefore be considered and included when calculating the SACF.
ABSTRACT
A new 4πß(LS)-γ digital coincidence counting (DCC) system has been developed at NIM. The system equipped with a triple-to-double coincidence ratio (TDCR) counter in the ß-channel and a NaI(Tl) scintillation detector in the γ-channel. A dedicated DCC software was designed for off-line implementation of 4πß(LS)-γ coincidence counting method. The software consists of three modules: software-based circuits module, dead-time and resolving-time correction module and efficiency extrapolation module, respectively. The performance of the newly developed 4πß(LS)-γ DCC system was demonstrated by a comparison measurement of Co-60 solution with the conventional 4πß(PC)-γ DCC system.
Subject(s)
Scintillation Counting , SoftwareABSTRACT
This paper presents the results of microstructural analysis of novel preceramic paper-derived SiCf/SiC composites fabricated by spark plasma sintering. The sintering temperature and pressure were 2100/2200 °C and 60/100 MPa, respectively. The content of fibers in the composites was approx. 10 wt %. The SiCf/SiC composites were analyzed by positron annihilation methods, X-ray diffraction technology, scanning electron microscopy, and Raman spectroscopy. Longer sintering time causes the proportion of the 6H-SiC composition to increase to ~80%. The increase in sintering temperature from 2100 °C to 2200 °C leads to partial transition of 4H-SiC to 6H-SiC during the sintering process, and the long-life component of positrons indicates the formation of Si vacancies. The Raman characteristic peaks of turbostratic graphite appear in the Raman spectrum of SiC fibers, this is caused by the diffusion of carbon from the surface of the SiC fiber and the preceramic paper during the high-temperature sintering process.
ABSTRACT
Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are promising materials for applications as structural components used under high irradiation flux and high temperature conditions. The addition of SiC fibers (SiCf) may improve both the physical and mechanical properties of CMCs and lead to an increase in their tolerance to failure. This work describes the fabrication and characterization of novel preceramic paper-derived SiCf/SiCp composites fabricated by spark plasma sintering (SPS). The sintering temperature and pressure were 2100 °C and 20-60 MPa, respectively. The content of fibers in the composites was approx. 10 wt.%. The matrix densification and fiber distribution were examined by X-ray computed tomography and scanning electron microscopy. Short processing time avoided the destruction of SiC fibers during SPS. The flexural strength of the fabricated SiCf/SiCp composites at room temperature varies between 300 and 430 MPa depending on the processing parameters and microstructure of the fabricated composites. A quasi-ductile fracture behavior of the fabricated composites was observed.
ABSTRACT
In this study, carbon nanorods (CNR) and graphene nanoribbons (GNR) derived from metal-organic frameworks (MOFs) were first prepared by solvothermal method. Then, Ni-Co layered double hydroxide (LDH)/CNR and LDH/GNR composite materials for supercapacitors were synthesized using a facile co-precipitation method. With the help of GNR, the Ni-Co LDH/GNR composite material showed great specific capacity (1765 F g-1), rate performance (68% capacity retention when current density increased from 1 to 20 A g-1) and cycling stability (83% capacity retention after 2000 charge-discharge cycles at 5 A g-1). Furthermore, an asymmetric supercapacitor (ASC) with Ni-Co LDH/GNR as positive and activated carbon (AC) as negative electrodes was fabricated. The ASC device delivered a high energy density of 25.4 W h kg-1 at power density of 749 W kg-1 and exhibited excellent cycling stability (96% specific capacity retention after 5000 cycles).
ABSTRACT
A defined solid angle counting apparatus for radon-222 activity absolute measurement is presented. Two home-made vacuum sealed radium-226 sources with radioactivity of 500kBq and 3MBq are used to minimize the impact from gas impurities. The defined solid angle is calculated using precisely measured geometrical parameters by several algorithms. The result from Monte Carlo simulation agrees with results obtained by other methods within the estimated uncertainty limit. Alpha particle's scattering behavior in the measurement chamber and collimator is simulated by the geant4 code and a total scattering alpha particle ratio of 0.23% as well as a relative uncertainty contribution to activity measurement of 0.02% to 0.09% are estimated. A typical total combined standard uncertainty of 0.28% is evaluated for the radon activity primary measurement.
ABSTRACT
The dielectric constant and electrical conductivity of a composite of two insulators, poly(1,1-difluoroethylene) (yellow) and K(2)CO(3) (white), increased dramatically near the percolation threshold f(c) (f=concentration of K(2)CO(3)). This intriguing phenomenon can be interpreted in terms of interface percolation caused by the formation of chemically activated interfaces.
