Kensuke Amemiya

Improvement of the Productivity in the THM Growth of CdTe Single Crystal as Nuclear Radiation Detector

The effect of the THM growth rate on the CdTe crystalline quality and the detector performance was intensively investigated. The maximum growth rate for the single crystal growth was found to be approximately 15 mm/day which was 3 times greater than the conventional one. By optimizing other growth conditions, 90% of every ingot volume has become a single crystal. Te inclusions in the CdTe single crystal grown at various growth rates were also investigated by IR transmission microscopy. There was no correlation between the behavior of Te inclusions and the growth rate. The detector performance was also independent of the growth rate. Taking advantage of the large volume CdTe single crystals, about 700 000 Schottky detectors with 4 mm × 7.5 mm × 1 mm were fabricated for the research and development of the new positron emission tomography (PET) system using CdTe detectors. The average FWHM for the 662 keV line from 137Cs and its standard deviation were 2.24% and 0.48%, respectively. This uniformity was essential for the development of the new PET system.

Simulation of Flying Height and Response Time of Thermal Flying Height Control Sliders With Thermal Insulators

Thermal flying height control (TFC) has recently been implemented in magnetic recording disk drives to reduce the flying height at the read/write element of magnetic recording sliders. This paper investigates the flying height and response time of TFC sliders with single and dual TFC heaters and thermal insulators. Simulation results show that the presence of a thermal insulator has little effect on the response time of thermal protrusions. In addition, the effect of the dimensions of a TFC heater on the flying height and thermal response time is important. For a given heater power, the dual TFC heater design with thermal insulators can provide a very flexible control over flying height and response time of TFC sliders.

Basic Performance Test of a Prototype PET Scanner Using CdTe Semiconductor Detectors

A prototype positron emission tomography (PET) scanner using CdTe semiconductor detectors was developed, and its initial evaluation was conducted. The scanner was configured to form a single detector ring with six separated detector units, each having 96 detectors arranged in three detector layers. The field of view (FOV) size was 82 mm in diameter. Basic physical performance indicators of the scanner were measured through phantom studies and confirmed by rat imaging. The system-averaged energy resolution and timing resolution were 5.4% and 6.0 ns (each in FWHM) respectively. Spatial resolution measured at FOV center was 2.6 mm FWHM. Scatter fraction was measured and calculated in a National Electrical Manufacturers Association (NEMA)-fashioned manner using a 3-mm diameter hot capillary in a water-filled 80-mm diameter acrylic cylinder. The calculated result was 3.6%. Effect of depth of interaction (DOI) measurement was demonstrated by comparing hot-rod phantom images reconstructed with and without DOI information. Finally, images of a rat myocardium and an implanted tumor were visually assessed, and the imaging performance was confirmed.

Negative ion beam production by a microwave ion source equipped with a magnetically separated double plasma cell system

Filamentless negative ion beam production was investigated with a compact microwave ion source (2.45 GHz). One of the key points for negative ion production is the magnetic configuration. A magnetic filter field to lower electron temperature was generated in a negative ion production cell, which was shielded magnetically from a discharge cell with a magnetic field to couple microwave to plasma. Production of H− beam was studied with this source. H− was extracted through a grid slit (2×16 mm2) from plasma and accelerated to 20–40 keV. H− beam current was measured with a Faraday cup after magnetic mass separation. Continuous H− beam current of 73 μA (0.23 mA/cm2) was obtained with a magnetron power of 700 W. H− beam current was increased around 1.4 times by adding Xe gas to the H2 gas. Other negative ion species, which have a potential for applications to industrial ion beam processing with little charge-up problem, were also investigated. Carbon and hydrocarbon negative ion beams were produced using boron ...

Ion beam acceleration using variable frequency RFQ

Abstract To develop a high-current MeV ion implanter, a beam acceleration feasibility study using a variable frequency RFQ system was carried out. The RFQ system consists of an LC tank circuit and conventional RFQ electrodes 60 cm in length. The resonance frequency was varied by changing the electrical capacity in the circuit. Experimental results show that injected N+ beams of 1.3 keV were accelerat frequency in the range of 12–15 MHz. The Q-value obtained was over 1500. Results show that a variable frequency RFQ system is suitable for application in MeV ion implantation.

New microwave ion source for high energy ion implanter

Abstract A new high current multiply-charged ion source, which is used for a high energy ion implanter, was designed to produce a mA-class multiply-charged ion beam. The discharge chamber is approximately four times larger than that of a conventional coaxial-type source and has a multipole magnetic field. An ion beam of a several mA is extracted from the new source and mass-analyzed. The extracted ion beam has an Ar 2+ beam of approximately 1 mA. The Ar 2+ /Ar + ratio obtained from this new source is 80%, which is a large improvement over the 10% of the conventional source. This ratio increases with absorbed microwave power.

Pulsed Bias Voltage Shutdown to Suppress the Polarization Effect for a CdTe Radiation Detector

Pulsed bias shutdown operation, in which the bias voltage supply is periodically shut down for a certain time, is suitable for suppressing the polarization effect in a CdTe radiation detector. The duration of the bias voltage shutdown should be short to decrease the dead time and ensure the continuity of the measurement; however, the polarization effect may not be suppressed if the duration is too short. Therefore, we investigated bias voltage shutdown durations and intervals that stabilize the detector performance. A stacked type detector consisting of four 1-mm-thick CdTe diodes was used. At 35degC, the energy resolution for the 511 keV photopeak of the 22 Na source saturates at around 30 min after the measurement start and then does not change up to 300 min when the bias voltage is shut down for 10 ms every 5 min. Similarly at 60degC, the energy resolution for the 511 keV photopeak is unchanged for 300 min when the bias voltage is shut down for 10 ms every 10 s.

Improvement of the productivity in the growth of CdTe single crystal by THM for the new PET system

The effect of the THM growth rate on the CdTe crystalline quality and the detector performance was intensively investigated. The maximum growth rate for the single crystal growth was found to be approximately 15 mm/day which was 3 times greater than the conventional one. By optimizing other growth conditions, 90% of every ingot volume has become a single crystal. Te inclusions in the CdTe single crystal grown at various growth rates were also investigated by IR transmission microscopy. There was no correlation between the behavior of Te inclusions and the growth rate. The detector performance was also independent of the growth rate. Taking advantage of the large volume CdTe single crystals, about 700,000 Schottky detectors with 4 mm times 7.5 mm times 1 mm were fabricated for the research and development of the new PET system using CdTe detectors. The average FWHM for the 662 keV line from 137Cs and its standard deviation were 2.24% and 0.48%, respectively. This uniformity was essential for the development of the new PET system. For the further improvement of productivity, the growth technology of a 100 mm diameter crystal by THM is in the development and is presented.

High energy aluminum ion implantation using a variable energy radio frequency quadrupole implanter

A high energy aluminum ion implantation using a variable energy radio frequency quadrupole (RFQ) implanter has been studied for the fabrication of high power semiconductor devices. The implanter consists of a microwave ion source with a crucible for AlCl3 sublimation, a sector type mass separator, a magnetic quadrupole triplet, a variable energy four-rod RFQ linac as an additional accelerator, an energy analyzer, and an implantation chamber. Al2+ ions, with energies of 1.0 MeV and 0.9 MeV, are implanted into a 6-inch diameter wafer, and the depth profile and dose uniformity are measured by secondary ion mass spectroscopy and sheet resistivity, respectively. Results show that the depth profile has the desired features for the projected range, and the dose non-uniformity is 0.7%.

Production of milliampere class mass‐separated multiply charged ion beam

A new type of microwave ion source for a megaelectron volt ion implanter is designed to produce milliampere class multiply charged ion beams. This ion source has a single stage plasma chamber with both a mirror and an octopole magnetic field to produce milliampere class lower‐charge‐state ions efficiently. The extracted ion beam is mass separated, and a Kr2+ beam of 2.3 mA and an Ar2+ beam of 3.0 mA are obtained with absorbed microwave powers of 700 and 570 W, respectively. Combination of this new source with an ion accelerator should realize a milliampere class megaelectron volt ion implanter.