Shunji Kishimoto

High time resolution x‐ray measurements with an avalanche photodiode detector

An avalanche photodiode (APD) detector has been developed for x‐ray timing measurements with a subnanosecond time resolution. The performance of the APD detector was investigated with synchrotron x‐ray beams in multi‐ and single‐bunch runs at the Photon Factory (PF) ring. A time resolution of 0.28 ns (FWHM) and a peak‐to‐background ratio of more than 107 were obtained from the main peak of 14.4‐keV x rays in a single‐bunch time spectrum. The intrinsic efficiency and the counting‐rate capability were also measured. As an application with a high time resolution, time spectra of quantum beats in nuclear resonance of 57Fe were observed with the APD detector at the undulator beam line BL‐NE3 of the TRISTAN accumulation ring; the first peak of the beats was completely separated from the prompt peak of the non‐nuclear components with a good time resolution and the beat structure was sharply seen to the range of ≳100 ns later with a very low background.

Origin of Fast Scintillation Components of LiCaAlF6 Crystals

The origin of the fast scintillation component of Ce-doped LiCaAlF6 crystal excited by gamma ray irradiation was studied with X-ray and vacuum ultraviolet (VUV) irradiation. A fast luminescence component was observed under VUV irradiation and was ascribed to luminescence at defects in the host matrix on the basis of VUV spectroscopy. No fast scintillation component was observed in the scintillation time profile under X-ray irradiation. The fast scintillation component under gamma ray irradiation can be concluded to be the result of Cherenkov radiation from energetic secondary electrons.

Imaging plate for time‐resolved x‐ray measurements (invited)

Two apparatus have been developed for time‐resolved measurements of x‐ray diffraction patterns using an imaging plate detector. The first one is based on a cinema method which permits up to 40 exposures of a two‐dimensional x‐ray pattern (100×108 mm2) with a 0.3‐s time resolution. The second one works as a 200‐mm‐long linear detector which enables a time resolution of 23 μs for a duration of up to 46 ms, based on a streak‐camera method. These apparatus have no count rate limitation, a high detective quantum efficiency (more than 80% for 8–20 keV), a 1:105 dynamic range in x‐ray intensity and a spatial resolution of 150 μm (FWHM) due to the performance of the imaging plate.

Subnanosecond time-resolved x-ray measurements using an organic-inorganic perovskite scintillator

We have developed a fast x-ray detector using an organic-inorganic perovskite scintillator of phenethylamine lead bromide (PhE-PbBr4). The scintillator had a dominant light emission with a fast decay time of 9.9 ns. An x-ray detector equipped with a 0.9-mm-thick PhE-PbBr4 crystal was used to detect nuclear resonant scattering in N61i (the first excited level: 67.41 keV; lifetime: 7.6 ns) by using synchrotron radiation. With this detector, we could successfully record the decaying gamma rays emitted from N61i with a time resolution of 0.7 ns (full width at half maximum) and a relatively high detection efficiency of 24%.

X-ray polarization anomaly of forbidden reflections of iron pyrite, FeS2, near the Fe K-absorption edge

X-ray polarization analysis of allowed and forbidden reflections from iron pyrite, FeS 2 , was carried out using synchrotron radiation. Since the incident beam was σ-polarized, the polarization of allowed reflections was also σ. However, the polarization of the forbidden reflections showed complex structure. From investigating the polarization and its azimuthal angle dependence, it was concluded that the reflections were caused by the ATS (Anisotropy of the Tensor of Susceptibility) scattering.

Development of an APD-Based PET Module and Preliminary Resolution Performance of an Experimental Prototype Gantry

The development of a high-resolution Positron Emission Tomography (PET) technique with sub-millimeter spatial resolution, which utilizes newly designed reverse-type APD-arrays, is uderway. All the detector blocks are modularized with the overall dimension of each module, including the APD array, LYSO scintillator matrix and Front-End Circuits (FECs), which are only 30 × 30 × 80 mm3. Each APD device also has a monolithic 16 × 16 pixel structure with an active area of 1.0 mm2 per pixel. The FEC includes two identical analog ASICs specifically designed for APDs with a noise characteristic of 560 + 30 e-/pF and a timing resolution of 460 ps (rms), respectively. An energy resolution of 13.7 ± 1.1% (FWHM) with 662 keV gamma-rays was measured using the 16 × 16 arrays. At this stage a pair of module and coincidence circuits has been assembled into an experimental prototype gantry. Spatial resolutions of 0.9, 1.4, and 1.3 mm (FWHM) were obtained from FBP reconstructed images in preliminary experiments with a point source positioned centrally, and 1 and 5 mm off-center, respectively. Comparison with a Monte-Carlo simulation of a fully-designed gantry over a wider range of field-of-view showed good correlation with the experimental data. A simple but conceptual design of a DOI configuration is also proposed as a test example of a future APD-PET scanner.

Fast signal processing of a yttrium–aluminum–perovskite:Ce detector for synchrotron x-ray experiments

An amplifier has been developed to form narrow pulses of less than 100 ns for a YAP:Ce scintillator, which appears promising as a detector for high-counting rate x-ray measurements. The performance of the detector system has been evaluated with monochromatic 8, 16.5, and 25 keV synchrotron x-ray photons at the Photon Factory. The whole deadtime obtained was 84 ns, which is around 3.5 times the decay time of the scintillation (25 ns), indicating that the present system is almost optimum. It has been found that the counting loss for 1 M counts/s is only 8%–9%, and that the detector can count extremely strong photons up to 5 M counts/s.

Behavior of a fast counting system with an avalanche photodiode detector for synchrotron X-rays

Abstract The behavior of a fast counting system with an avalanche photodiode (APD) detector was examined using X-rays produced by synchrotron radiation. The system with the APD detector had a dead time of about 4ns. This provided superior performance with a count-rate capability of up to 108 counts/s in a multi-bunch mode of a storage ring. The relation between the input photon rates and the observed count rates is given based on a model for pulsed X-rays. The model well explains the behavior of a system with the APD detector in a single-bunch mode and at input rates below 108 photons/s in a multi-bunch mode. However, at higher rates the shape and variable amplitude of the pulse from an amplifier cause a difference from the behavior predicted by the model.

RECENT DEVELOPMENTS IN THE AVALANCHE PHOTODIODE X-RAY DETECTOR FOR TIMING AND FAST COUNTING MEASUREMENTS

An avalanche photodiode (APD) detector using a new silicon device has been developed for x‐ray timing measurements. The device, Model No. S5343 (Hamamatsu Photonics), has an excellent time resolution of 0.10 ns and has only a short tail, or a full width of 1.41 ns at 10−5 maximum, in the response function for the time spectrum. Measurements of the purity between the main and second bunches to the order of 10−9 were successfully executed in observing the bunch structure of the Photon Factory ring with the detector as an application to the bunch‐purity monitor. The APD detector also has a property for fast counting up to the order of 108 counts per second by using its output width, shorter than several nanoseconds. The count‐rate property has been examined with the pulsed beams of synchrotron radiation and with an APD device Model No. C30817E (EG&G Optoelectronics), which has a depletion layer about 100 μm thick. The results show that the count‐rate response can almost be expressed by a counting model for t...

X-ray detection capability of a BaCl2 single crystal scintillator

The x-ray detection capability of a scintillation detector equipped with a BaCl2 single crystal was evaluated. The scintillation decay kinetics can be expressed by a sum of two exponential decay components. The fast and slow components have lifetimes of 1.5 and 85 ns, respectively. The total light output is 5% that of YAP:Ce. A subnanosecond timing resolution was obtained. The detection efficiency of a 67.41 keV x-ray is 87% for a detector equipped with a BaCl2 crystal 6-mm thick. Thus, excellent timing resolution and high detection efficiency can be simultaneously achieved. Additionally, luminescence decay characteristics under vacuum ultraviolet excitation have been investigated. Radiative decay of self-trapped excitons is thought to be responsible for the fast scintillation component.