Search

Kernel averaging misorientation (KAM) measurements and positron annihilation lifetime spectroscopy (PALS) were conducted to investigate the damage introduced by the tensile and fatigue testing of type 316L stainless steel. The fatigue tests were carried out at room temperature and at 550 °C under the strain controlled mode with total strain amounts, Δe of 0.4% and 1.5%. A number of different samples were prepared by interrupting the fatigue test at various ratios of fatigue cycle time to fatigue lifetime. Both KAM and PALS analyses indicated increasing damage as increasing misorientation average or number of vacancies with increasing strains in tensile- and fatigue-tested samples. Dislocations play an important role in the evolution of damage as they produce vacancies and form dislocation structures. In the fatigue test at high temperature, accelerated dislocation relaxation encourages formation of dislocation structures that result in an early increase in misorientation. Under the same conditions, the positron lifetime rather decreased because of the migration of defects at early stages of fatigue and rapidly increased at fracture. We observed different responses to mechanical straining that can be useful for evaluation of damage in 316L stainless steel.

We have designed and been constructing a compact accelerator-driven neutron facility for Bragg edge transmission imaging of structural materials to obtain position dependent crystallographic information. In order to combine a high neutron wavelength resolution, which is especially required for strain measurements, and an intense neutron beam flux at the sample position, which is required for obtaining high quality statistics within practical measurement times, the components of the neutron facility are optimized. To achieve a high wavelength resolution while maintaining an intense neutron beam flux at the sample position, a solid methane decoupled cold moderator at about 20 K coupled with neutron guide tubes is employed. The target–moderator system, especially the moderator thickness was optimized using the Monte-Carlo simulation code PHITS. Neutrons will be produced using a 35-MeV electron accelerator which is currently under construction. The accelerator has a design maximum beam power of 10 kW, a maximum repetition rate of 100 Hz and a maximum pulse width of 10 μ s . The combination of the flight path length of about 8 m and the repetition rate is suitable for efficient Bragg edge measurements. The pulse width of the electron beam is suitable to achieve a high wavelength resolution with the solid methane decoupled moderator. The estimated flux of the neutron beam at the sample position is 1.2 × 104 ∼ 4 . 5 × 104 /cm2/s depending on the usage of super mirror guide tubes. The wavelength resolution at the sample is 0.5 ∼ 0.7% in the wavelength region from 0.3 to 0.4 nm.

To comprehensively investigate the correlation between free volume properties (size and distribution) in the interior of polyamide (PA) active layer and mass transport mechanism, six polyamide thin film composite (TFC) membranes were characterized using positron annihilation lifetime spectroscopy (PALS). In case of pressurized filtration conditions, the rejection rate of boron across all PA membranes was found to be inversely proportional to the free volume size. The more boron transport occurred at the membrane containing larger free volume. In addition, the transition of the neutral boron transport mechanism from convection to diffusion was found to occur at a membrane free volume radius around 0.275 nm within the applied pressure range (2 and 10 bar), as verified by PALS and the dimensionless Peclet number. We believe that mass transport mechanism transition from convection to diffusion is caused by the compression of polyamide active layer due to applied hydraulic pressure (10 bar), resulting in lowering the convective mass transport pathway inside polyamide active layer. These membrane free volume size criteria and experimental filtration results may subsequently be used as new design guidelines for the development of high boron rejection polyamide TFC membranes having a low energy consumption.

We systematically investigate the pore structure of cellulose triacetate (CTA) and polyamide (PA) forward osmosis (FO) membranes with positron annihilation lifetime spectroscopy (PALS) and fractional rejection (FR) method to better understand the relationship between membrane pores (atomic-scale free volume) and separation performance. The results reported in this study suggest a range of membrane pore sizes and inner structures appropriate for the osmotic membrane process regardless of membrane materials. The PALS data suggest that the active layer of both FO membranes is mainly composed of generally uniform pores of larger size (0.29−0.30 nm) compared to seawater reverse osmosis (SWRO) (0.20−0.24 nm) membranes. The membrane pore size distribution (PSD) deduced by the FR method suggest that the PSD of both FO membranes are significantly shifted to smaller sizes under pressurized conditions, possibly due to the overall compression of the FO membranes. The effects of applied pressure on the structure and performance of active layer should be further investigated along with other properties such as thickness, swelling and sorption properties.

The electron emission properties of a coniferous carbon nano-structure (CCNS) based field emission electron gun have been measured. The CCNS was grown on a stainless steel substrate using chemical vapor deposition (CVD) and biased to about 50 kV. Stable, high-current-density electron emission (102 mA/cm 2 ) was measured continuously for more than 1300 h. This result compares favorably to printed and directly grown carbon nanotube (CNT) based emitters. A wide range of potential applications are foreseen for CCNS based electron emitters, such as high intensity X-ray sources.

A Zero-Boil-Off (ZBO) cryostat is designed to realize a compact, stand-alone cryogenic system for the AIST superconducting accelerator (SCA). Under normal operation there is no evaporative helium loss from the cryomodule and therefore operating costs associated with the supply of liquid helium can be eliminated. The only significant loss of helium from the module occurs during the initial cavity cool-down procedure or when the re-condensing cryostat is replaced. It takes about 3 h to cool down the cryostat head from room temperature (300 K) to 4 K. During this time around 100 L of liquid helium is lost due to evaporation. By pre-cooling the cryostat inside a low heat load vacuum tube before transfer to the cryomodule, this evaporative loss could be essentially eliminated, significantly reducing the volume of liquid helium required for the initial cryomodule cool-down. The pre-cooling system also provides an efficient method to test the cryostat prior to use.

A new photon-induced positron annihilation lifetime spectroscopy approach has been developed using an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). The high energy ( 42 MeV ), intense (105 photons pulse−1), and ultra-short pulse (3 ps pulse width) photon beam creates positrons throughout an entire sample via pair production. A positron lifetime spectrum can be obtained by measuring the time difference between the accelerator's RF frequency and the detection time of the annihilation gamma rays. The positron lifetimes for lead and yttria-stabilized zirconia samples have been successfully measured.

A slow-positron beam system for in-situ positron lifetime measurements during ion beam irradiation is currently under development in order to obtain fundamental information on radiation-induced defects. The system uses a high-intensity positron beam generated through pair-creation by a 70 MeV electron beam from a linear accelerator. The system has typical pulsing electrodes for chopping and bunching positrons. The incident directions of positrons and ions are 0° and 45° to the surface normal of samples, respectively. H, He and inert-gas ions up to 150 keV can be introduced to a target chamber with the irradiation temperature variable from room temperature to 600 °C. In a preliminary examination of the beamlines, 150 keV Ar+, electrons from a photocathode and positrons from a radioisotope were successfully transported to the target chamber from their respective sources. In addition, in-situ lifetime measurements using the existing positron beamline were demonstrated.

Decay dynamics of dielectronic recombination (DR) processes of H-like titanium ions was investigated with an electron beam ion trap. In the DR of H-like ions a K-shell vacancy is available even after the decay of the doubly excited state produced by the recombination. Therefore secondary X-ray emission is possible. An observed X-ray spectrum of DR obtained in the present experiment was well reproduced theoretically by taking into account the secondary X-rays.

Highly charged argon ions, Ar7+,8+ with kinetic energy of several keV, have been used to irradiate dodecanethiol self assembled monolayers. The irradiated samples were then imaged in situ by scanning tunneling microscopy. Comparisons between un-irradiated and irradiated surfaces showed the appearance of a number of small defects or ‘nanocraters’ in the regular domains of the monolayer after ion impact. Single nanocrater is produced by individual highly charged ion impact. The origin of the craters is analyzed by performing a time of flight study of desorbed positive ions.

The conceptual design of a new electron beam ion trap primarily intended for the study of electron–ion interactions is outlined along with some preliminary predictions regarding its capabilities.

We have determined resonant strengths of the KLn ð2 6 n 6 5Þ resonances for helium-like Ti ions and ð3 6 n 6 5Þ resonances for helium-like Fe ions. The results were obtained using the Tokyo electron beam ion trap. Characteristic X-rays from both dielectronic recombination and radiative recombination were detected as the electron beam energy was scanned through the resonances. 2003 Elsevier Science B.V. All rights reserved.

Electron beam trajectory simulations have been performed to design a new electron beam ion trap. The design of the magnet and electrode structures was optimized based on the results of the simulations.

We have measured electron impact ionization cross-sections of hydrogen-like iron and hydrogen-like molybdenum with an electron beam ion trap. The measurements were performed in the electron energy range between 13.5 and 40 keV for hydrogen-like iron and between 50 and 80 keV for hydrogen-like molybdenum.