Takehiro Shimaoka

Pulse height reduction effects of single-crystal CVD diamond detector for low-energy heavy ions

The performance of a diamond detector made of single-crystal diamond grown by chemical vapour deposition was studied for heavy ions, having energy of 3 MeV. Energy peaks of these low-energy ions were clearly observed. However, the pulse height for individual incident ion decreases with increasing atomic number of the ions. For understanding this pulse height reduction effect, we calculated the amount of ionizing and non-ionizing energy loss of incident ions in the diamond detector. The results of our calculation suggest the contribution of charge loss mechanisms other than the recombination effect of electron-hole pairs produced along the ionized track. We also mentioned the incomplete charge collection near the boundary region between the metal electrode and the diamond surface.

High-performance diamond radiation detectors produced by lift-off method

For stable semiconductor detector operation under harsh environments, an ideal single-crystal diamond without a charge trapping centre is required. For this study, a self-standing single-crystal CVD diamond was fabricated using a lift-off method. The reduction of charge trapping factors such as structural defects, point defects, and nitrogen impurities, was attempted using 0.2% of low-methane concentration growth and using a full metal seal chamber. A high-quality self-standing diamond with strong free-exciton recombination emission was obtained. Charge collection efficiencies were 100.1% for holes and 99.8% for electrons, provided that and . Energy resolutions were 0.38% for both holes and electrons. We produced a high-performance diamond radiation detector using the productive lift-off method.

Single-crystal CVD diamond detector for high-resolution particle spectrometry

The performance of a single-crystal diamond detector, grown by chemical vapour deposition, as an energy spectrometer for charged particles was studied. The detector was able to identify four different energies of -particles (5.389, 5.443, 5.486, and 5.545 MeV) thanks to a superior intrinsic energy resolution of (full width at half maximum). The electrode configuration, specifically the electric field configuration inside the diamond crystal, and the electrode materials, strongly affect the energy resolution for charged particles. The charge collection efficiency inside the diamond crystal was for both electrons and holes.

A diamond 14 MeV neutron energy spectrometer with high energy resolution

A self-standing single-crystal chemical vapor deposited diamond was obtained using lift-off method. It was fabricated into a radiation detector and response function measurements for 14 MeV neutrons were taken at the fusion neutronics source. 1.5% of high energy resolution was obtained by using the (12)C(n, α)(9)Be reaction at an angle of 100° with the deuteron beam line. The intrinsic energy resolution, excluding energy spreading caused by neutron scattering, slowing in the target and circuit noises was 0.79%, which was also the best resolution of the diamond detector ever reported.

Dependence of scintillation properties on cerium concentration for GPS single crystal scintillators grown by a TSSG method

Single crystal Gd<inf>2</inf>Si<inf>2</inf>O<inf>7</inf>:Ce (GPS:Ce) scintillators were grown by a top seeded solution growth (TSSG) method and their crystal structures and scintillation properties were measured. Single crystal GPS with several cerium concentration; (Gd<inf>1‒x</inf>Ce<inf>x</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (x=0.025, 0.1, 0.15), were synthesized with a RF-Czochralski furnace. For GPS:Ce 2.5 at.%, a crystal structure was orthorhombic. For GPS:Ce 10 and 15 at.%, these were triclinic. In PL measurements, broad emissions around 350 to 450 nm correspond to 5d–4f transitions of Ce³⁺ were observed. In gamma-ray measurements, each scintillator shows light output larger than that of BGO. High energy resolution of around 5% was obtained for GPS:Ce 2.5 and 10 at.%. GPS:Ce 2.5 at.% shows ca. 4.4 times light output larger than that of BGO. Decay times of triclinic GPS were faster than that of orthorhombic GPS.

Charge-collection efficiency and long-term stability of single-crystal CVD diamond detector under different carrier-drift conditions

We investigate the performance of a charged-particle detector fabricated using single-crystal diamond grown by chemical vapor deposition. The detector identified four different 241Am α-particle energies (5.389, 5.443, 5.486, and 5.545 MeV) thanks to its superior energy resolution of 0.407 ± 0.004% for electron drift and 0.418 ± 0.004% for hole drift (full width at half maximum). The charge-collection efficiency inside the diamond crystal was above 97.0% for both electrons and holes. The diamond detector also exhibited no significant degradation in terms of pulse-height spectra and energy resolution during operation for more than 100 h under electron-drift conditions. In contrast, the pulse-height spectra obtained under hole-drift conditions deteriorated because of the polarization phenomenon.

Single-crystal CVD diamond detector for low-energy charged particles with energies ranging from 100 keV to 2 MeV

The performance of a diamond detector made of a single-crystal diamond grown by chemical vapor deposition was studied for charged particles, having energies ranging from 100 keV to 2 MeV. Energy peaks of these low-energy ions were clearly observed. However, we observed that the pulse height for individual incident ion decreases with increasing atomic number of the ions. We estimated the charge collection efficiency of the generated charge carriers by charged particle incident. The charge collection above ~95% is achieved for helium (He+) with the energy above 1.5 MeV. On the other hand, the charge collection efficiency for heavy-ions shows lower values compared with that of He+, ~70% for silicon (Si+) and ~30% for gold (Au3+), at the same incident energy range, respectively.

Response measurement of single-crystal chemical vapor deposition diamond radiation detector for intense X-rays aiming at neutron bang-time and neutron burn-history measurement on an inertial confinement fusion with fast ignition

A neutron bang time and burn history monitor in inertial confinement fusion with fast ignition are necessary for plasma diagnostics. In the FIREX project, however, no detector attained those capabilities because high-intensity X-rays accompanied fast electrons used for plasma heating. To solve this problem, single-crystal CVD diamond was grown and fabricated into a radiation detector. The detector, which had excellent charge transportation property, was tested to obtain a response function for intense X-rays. The applicability for neutron bang time and burn history monitor was verified experimentally. Charge collection efficiency of 99.5% ± 0.8% and 97.1% ± 1.4% for holes and electrons were obtained using 5.486 MeV alpha particles. The drift velocity at electric field which saturates charge collection efficiency was 1.1 ± 0.4 × 10(7) cm/s and 1.0 ± 0.3 × 10(7) cm/s for holes and electrons. Fast response of several ns pulse width for intense X-ray was obtained at the GEKKO XII experiment, which is sufficiently fast for ToF measurements to obtain a neutron signal separately from X-rays. Based on these results, we confirmed that the single-crystal CVD diamond detector obtained neutron signal with good S/N under ion temperature 0.5-1 keV and neutron yield of more than 10(9) neutrons/shot.

Pulse shape distortion of output signals from single-crystal CVD diamond detector in few-GHz broadband amplifiers

The response of a diamond detector made from a single crystal grown by chemical vapour deposition was studied using a broadband amplifier. A short pulse width of for 241Am-?-particles was observed with a digital oscilloscope. To discuss pulse shape distortion from the detector in a measurement system, we simulated waveforms with a SPICE simulator using an equivalent circuit model that contained three main parts: detector, amplifier, and oscilloscope. In the simulation, we found that the pulse width spread by more than 200 ps following amplification. We discuss the effects of the detector read-out circuit time constant on the observed waveforms and confirm that the pulse width spread was restrained by use of a short time constant compared with carrier drift time in diamond crystals.