Microstructure Evolution during Radiation Damage with Collision Cascades

Progress of the research on microstructural evolution during radiation damage accompanied with collision cascades, particularly by neutrons, is summarized from the research papers published since 1992. The major part of irradiation was performed with JMTR (Japan Materials Testing Reactor), and comparisons were made with the result of D-T fusion neutron irradiation with RTNS-II (Rotating Target Neutron Source, LLNL). The subjects concerned are : (1) Correlation of high-energy particle irradiation by use of the recoil energy spectrum, (2) Cascade localization induced bias effect for void growth, (3) Influence of primary recoil energy spectrum on microstructural evolution, (4) Variation of the cascade localization induced bias effect with material parameters and irradiation conditions, (5) Fluctuation effect of point defect reaction on nucleation of interstitial clusters, (6) Binary collision calculation of subcascade structure and its correspondence to observed subcascade defects in 14 MeV neutron irradiated copper, (7) Detection of the role of free point defects from the variation of defect structures near permanent sinks, (8) Low dose fission neutron irradiation on P- and Ti-modified austenitic alloys with improved temperature control, (9) Role of free point defects in defect structure evolution during cascade damage, (10) Origin of unbalanced reaction of vacancies and interstitial during irradiation with cascades and influence on microstructural evolution, (11) Influence of details of reactor history on microstructural development, (12) Exposure time and recoil energy dependence of defect accumulation, (13) Development of controlled temperature-cycle irradiation technique in JMTR, (14) Microstructure evolution by neutron irradiation during cyclic temperature variation, (15) Role of solute atoms on microstructural evolution in neutron irradiated nickel, (16) Microstructural evolution in low dose neutron irradiated Fe-15Ni-15Cr alloy, and (17) Effect of cascade localization induced bias effect and fluctuation of point defect reactions on defect structure evolution near planar sinks

VARIABLE LATENT VACANCY MECHANISM OF DIFFUSION IN AMORPHOUS METALS

A model which is pertinent to describle the characteristics of atomic diffusion in amorphous metals is proposed. The process corresponding to the thermal equilibrium generation of diffusion carriers such as lattice vacancies in crystalline metals is sought in the thermally reversible change of already existing vacancy like positions to the state of easier activation for their motion. Discussions on the temperature dependence of diffusion speed is given from the proposed variable latent vacancy mechanism

Local-Circuit Phenotypes of Layer 5 Neurons in Motor-Frontal Cortex of YFP-H Mice

Layer 5 pyramidal neurons comprise an important but heterogeneous group of cortical projection neurons. In motor-frontal cortex, these neurons are centrally involved in the cortical control of movement. Recent studies indicate that local excitatory networks in mouse motor-frontal cortex are dominated by descending pathways from layer 2/3 to 5. However, those pathways were identified in experiments involving unlabeled neurons in wild type mice. Here, to explore the possibility of class-specific connectivity in this descending pathway, we mapped the local sources of excitatory synaptic input to a genetically labeled population of cortical neurons: YFP-positive layer 5 neurons of YFP-H mice. We found, first, that in motor cortex, YFP-positive neurons were distributed in a double blade, consistent with the idea of layer 5B having greater thickness in frontal neocortex. Second, whereas unlabeled neurons in upper layer 5 received their strongest inputs from layer 2, YFP-positive neurons in the upper blade received prominent layer 3 inputs. Third, YFP-positive neurons exhibited distinct electrophysiological properties, including low spike frequency adaptation, as reported previously. Our results with this genetically labeled neuronal population indicate the presence of distinct local-circuit phenotypes among layer 5 pyramidal neurons in mouse motor-frontal cortex, and present a paradigm for investigating local circuit organization in other genetically labeled populations of cortical neurons

Ephus: Multipurpose Data Acquisition Software for Neuroscience Experiments

Physiological measurements in neuroscience experiments often involve complex stimulus paradigms and multiple data channels. Ephus (http://www.ephus.org) is an open-source software package designed for general-purpose data acquisition and instrument control. Ephus operates as a collection of modular programs, including an ephys program for standard whole-cell recording with single or multiple electrodes in typical electrophysiological experiments, and a mapper program for synaptic circuit mapping experiments involving laser scanning photostimulation based on glutamate uncaging or channelrhodopsin-2 excitation. Custom user functions allow user-extensibility at multiple levels, including on-line analysis and closed-loop experiments, where experimental parameters can be changed based on recently acquired data, such as during in vivo behavioral experiments. Ephus is compatible with a variety of data acquisition and imaging hardware. This paper describes the main features and modules of Ephus and their use in representative experimental applications

Dislocation Loop Formation and Growth under In Situ Laser and/or Electron Irradiation

Vacancies and interstitial atoms are primary lattice (point) defects that cause observable microstructural changes, such as the formation of dislocation loops and voids in crystalline solids. These defects' diffusion properties determine the phase stability and environmental resistibility of macroscopic materials under ambient conditions. Although in situ methods have been proposed for measuring the diffusion energy of point defects, direct measurement has been limited. In this study, we propose an alternative in situ method to measure the activation energy for vacancy migration under laser irradiation using a pulsed laser beam from a laser-equipped high-voltage electron microscope (laser-HVEM). We made in situ observations that revealed the formation and growth of vacancy dislocation loops in an austenitic stainless steel during laser irradiation. These loops continued to grow when thermal annealing was performed after laser irradiation at the same temperature. We anticipate that laser-HVEM will provide a new method for investigating lattice defects

Thermal Evolution of the Proton Irradiated Structure in Tungsten–5 wt% Tantalum

We have monitored the thermal evolution of the proton irradiated structure of W–5 wt% Ta alloy by in-situ annealing in a transmission electron microscope at fusion reactor temperatures of 500–1300 °C. The interstitial-type a/2 dislocation loops emit self-interstitial atoms and glide to the free sample surface during the early stages of annealing. The resultant vacancy excess in the matrix originates vacancy-type a/2 dislocation loops that grow by loop and vacancy absorption in the temperature range of 600–900 °C. Voids form at 1000 °C, by either vacancy absorption or loop collapse, and grow progressively up to 1300 °C. Tantalum delays void formation by a vacancy-solute trapping mechanism