Takashi Miyachi

Study of the characteristics of a piezoelectric lead zirconate titanate radiation detector using a pulsed xenon source

The detector characteristics of piezoelectric lead zirconate titanate (PZT) were studied by directly irradiating a multilayered PZT detector with 400 MeV/n xenon ions. An extracted beam was processed with a rotating slit. Thus, passed through ∼103 xenon ions were available for 50 to 250u2002μs. The effect of polarization on the output signal was discussed, and the optimal electrode configuration was determined. The output signal appeared as an isolated pulse whose amplitude was qualitatively understood by the Bethe–Bloch formula. However, the calculated and the observed values differed depending on the rotation speed of the slit. A process that can explain the differences is presented here. The output signal appearing beyond the range of 400 MeV/n xenon ion beam was discussed. The sensitivity was compared with that obtained with hypervelocity collision of dust.

The Kaguya gamma-ray spectrometer: instrumentation and in-flight performances

A Gamma-Ray Spectrometer (GRS) had been developed as a part of the science payload for the first Japanese lunar explorer, Kaguya. The Kaguya was successfully launched from Tanegashima Space Center on September 14, 2007 and was injected into an orbit around the Moon and the mission ended on June 11, 2009. The Kaguya GRS (hereafter KGRS) has a large-volume Ge semiconductor detector of 252 cc as the main detector and bismuth-germanate and plastic scintillators as an active shielding. The Ge detector achieved an energy resolution of 3.0 keV (FWHM) for 1332 keV gamma ray in ground test despite the use of a mechanical cryocooler and observed gamma rays in energies ranging 0.2 to 12 MeV in lunar orbit. It was the first use of a Ge detector for lunar exploration. During the mission, KGRS participated in geochemical survey and investigated the elemental compositions of subsurface materials of the Moon. In this paper, we summarize the overview of the KGRS describing the design and in-flight performance of the instrument. This paper provides basic information required for reading science articles regarding the KGRSs observation data.

Study of Deterioration in a Piezoelectric Lead Zirconate Titanate Radiation Detector through Measurement of the Electromechanical Coupling Factor with 400 MeV/n Zenon Ions

The variation of the electromechanical coupling factor (ECF) was measured by bombarding a piezoelectric lead zirconate titanate (PZT) element with 400 MeV/n xenon ions. The element was exposed to energies up to 104 J, during which time the ECF was observed by the resonance method. The ECF gradually decreased with the energy accumulated during irradiation, and its behavior was scaled with an empirical formula. This decrease suggests that the piezoelectric quality deteriorated; hence, the sensitivity of the PZT radiation detector was considered to be degraded as well. The variation ultimately originated in resonance-associated processes. A potential detector suitable for use in severe-radiation environments was discussed.

Variation in resonant frequency of piezoelectric lead-zirconate-titanate element undergoing high-level radiation

A piezoelectric lead–zirconate–titanate (PZT) element was exposed to a 400 MeV/n xenon beam and the radiation effect on the element was studied as a variation of resonant and antiresonant frequencies by the resonance method. A possible effect of heating the element on the resonant frequency was avoided by using data obtained while the temperature of the element was kept constant. Consequently, the variation of the resonant frequency was empirically represented by a simple function of the amount of accumulated energy in the element. We therefore discuss the piezoelectric PZT element as a potential detector for high-level radiation. We point out that a piezoelectric equation including the heat term is required to explain the experimental results.

Dust detector using piezoelectric lead zirconate titanate with current-to-voltage converting amplifier for functional advancement

This paper describes the concept of a dust monitor using lead zirconate titanate (PZT) ceramics with a large detection area. Its potential as a dust detector is experimentally demonstrated. The dust monitor has a small volume compared to an impact ionization detector with the same detection area, due to the PZT sensor. The PZT sensor, as a traditional device for the in-situ observation of hypervelocity dust particles, has been used for momentum measurement. The hypervelocity impact signals of PZT sensors are typically read by charge-sensitive amplifiers. Instead, we suggest a new method that a current-to-voltage converting amplifier is useful for interpreting the impact signal of a PZT sensor arising from dust particles down to 0.5 μm in radius. We propose that datasets of dust impacts can be obtained with a higher statistical accuracy, if the new method is applied to instruments on forthcoming interplanetary-space-cruising spacecrafts.

Response of piezoelectric lead zirconate titanate to high-energy xenon ion beam pulse

To develop a new radiation detector, the characteristics of piezoelectric lead zirconate titanate (PZT) are currently being studied using a 400 MeV/n xenon (Xe) beam. In this study, the response of the PZT element to the pulsed beam was investigated by changing the beam intensity. It was found that the time distribution of the Xe ions in the pulse duration must be taken into account to understand the formation of the output signal that appeared on the PZT element.

Influence of a Polyimide Surface Layer on the Piezoelectric Response of Lead–Zirconate–Titanate Cosmic Dust Detector

The influence of a thermal reflector on the sensitivity of a lead–zirconate–titanate element is studied by bombarding the element with hypervelocity microparticles. The reflector is a 60-µm-thick layer made of polyimide resin that coats the surface of the element. By applying the fast Fourier transform method to data analysis, impact information is obtained through the fundamental resonant component. As a result, the sensitivity of the element is considerably reduced by the reflector. In addition, it is found that the sensitivity is substantially position-independent.

Gamma-ray spectrometer of high purity germanium detector cooled by the Stirling cycle cryostat in the lunar mission SELENE

The gamma ray spectrometer (GRS) will be onboard the Japanese lunar polar orbiter SELENE, to be launched in 2004, to obtain the information of element abundance on the entire lunar surface. GRS consists of a high-purity Ge detector as a main detector, which is an n-type Ge crystal with a high detection efficiency of 60% encapsulated in an aluminum canister. In addition, BGO and plastic scintillators are employed for an anti-coincidence shield and for suppression of Compton photons and energetic ion backgrounds. GRS will be the first gamma ray spectrometer employing a Ge detector for the lunar mission. GRS adopted a Stirling cycle refrigerator, whose cooling capacity is 2.0 W at 80 K. The mechanical vibration from the cryosystem to the Ge detector is effectively reduced by the dual opposed pistons in the compressor and the flexible thermo-coupling link between the two components. An excellent energy resolution of <3 keV at 1.33 MeV has been achieved in the prototype-model of GRS.