Taizo Kawauchi

Apparatus for time-resolved and energy-resolved measurement of internal conversion electron emission induced by nuclear resonant excitation with synchrotron radiation

A high-energy and large-object-spot type cylindrical mirror analyzer (CMA) was constructed with the aid of electron trajectory simulations. By adopting a particular shape for the outer cylinder, an energy resolution of 7% was achieved without guide rings as used in conventional CMAs. Combined with an avalanche photodiode as an electron detector, the K-shell internal conversion electrons were successfully measured under irradiation of synchrotron radiation at 14.4 keV in an energy-resolved and time-resolved manner.

Performance Recovery of Silicon-Avalanche- Photodiode Electron Detector by Low-Temperature Annealing

We report that the silicon avalanche photodiode (APD) for electron detection almost fully recovers from the damage caused by electron irradiation by annealing. With the electron irradiation at an energy of 8 keV, a prominent increase of the non-amplified component of the dark current was observed, and the gain and energy resolution for APD were significantly lowered. Upon annealing at 500 K for 10 h, the dark current was reduced and the gain and energy resolution were recovered. We also show that the dark current of APD depends on the material of the surface protection layer. The origin of the degradation and recovery is discussed.

Effect of electron irradiation dose on the performance of avalanche photodiode electron detectors

Avalanche photodiodes (APDs) are efficient detectors for electrons with energies below 100 keV. The damaging effects of 8 keV electron beam irradiation on the dark current and the output signal of the APD detector were investigated in this study. The APD dark current increases after electron doses exceeding 1.4×1013 cm−2. Preirradiation by high doses of 8 keV electrons further causes a deformation of the pulse height distribution of the APD output in the subsequent detection of low-flux electrons. This effect is particularly prominent when the energy of the detected electrons is lower than that of the damaging electrons. By comparing the experimental data with results of a simulation based on an electron trapping model, we conclude that the degradation of the APD performance is attributable to an enhancement of secondary-electron trapping at irradiation induced defects.

Hydrogen Redistribution and Performance Improvement of Silicon Avalanche Photodiode by Low-Temperature Annealing

We report the performance improvement of the silicon avalanche photodiode (APD) for electron detection by annealing. It was found that the dark current is reduced and that the gain and energy resolution are improved by annealing at 500 K for 10 h. By means of the nuclear reaction analysis, the depth distribution of hydrogen in APD was measured before and after annealing. The hydrogen concentration in the near-surface region was significantly increased by annealing. We discuss that passivation of the impurity and/or defect levels by hydrogen atoms is a possible reason for the performance improvement of the photodiode.

Nuclear resonant scattering of synchrotron radiation by physisorbed Kr on TiO2(110) surfaces in multilayer and monolayer regimes

Physisorbed Kr layers on TiO2(110) surfaces were investigated by means of nuclear resonant scattering (NRS) of synchrotron radiation at Kr thicknesses ranging from multilayer to monolayer. The NRS intensity was measured as a function of the Kr exposure, from which the NRS signal corresponding to monolayer was estimated as 0.23 cps. The time spectra measured at various thicknesses showed a monotonous decay without any quantum beat features. The recoilless fraction f evaluated from the analysis of the time spectrum revealed a substantial reduction upon temperature rise from 19 to 25 K. As its origin, an order-disorder phase transition of the monolayer Kr is proposed.