Hisashi Morii

Atomic Number and Electron Density Measurement Using a Conventional X-ray Tube and a CdTe Detector

In order to apply the dual-energy technique to material identification, a new computed tomography scanning system was proposed using a conventional X-ray tube and a CdTe detector. This system can provide information of projection data at two distinct energy bands for scanned materials. After introducing an approximation, the measured projection data were reconstructed to obtain the distributions of the X-ray linear attenuation coefficients of the materials at two different energies. Then, the corresponding atomic number and electron density can be derived with the dual-energy X-ray computed tomography (DXCT) method adopted. By comparing the obtained results with theoretical ones, the feasibility of using this system for identifying low-Z materials was demonstrated in this study.

Application of CdTe photon-counting x-ray imager to material discriminated x-ray CT

We proposed that material discriminated X-ray CT with conventional X-ray tube and energy differentiation type 64ch CdTe radiation line sensor. Distribution of Atomic number was obtained by using dual-energy X-ray CT. In this study, problem of conventional X-ray tube was reduced by the collimator and measurement time. So line attenuation coefficient was obtained depend on theory. Atomic number was calculated with two different methods. We could obtain atomic number within about three error margin.

Material discriminated x-ray CT by using conventional microfocus x-ray tube and cdte imager

Material discriminated X-ray CT system has been constructed by using conventional micro-focused X-ray tube (small white X-ray source) and photon counting type CdTe X-ray imager with energy-band discriminate function. We have already reported material identify X-ray CT using K-shell edge data. In this report the principle of material discrimination was adapted the separation of electron-density and atomic number from attenuation coefficient mapping in X-ray CT reconstructed image in dual energy X-ray CT method. The dual energy X-ray method was obtained good electron-density mappings by using two monochrome X-ray source, however, it is difficult for very large-scale equipment such as an accelerator to be necessary and to apply this system to homeland security field at the airport and so on. The measurement sample was prepared as three kinds material rods (aluminum(Al), titanium(Ti) ,iron(Fe) of 6mm-diameter). We could observed material discriminated X-ray CT reconstructed image, however, the discrimination properties were not good than two monochrome X-ray CT method. This results was could be explained because X-ray scattering, beam-hardening and so on based on white X-ray source, which could not observe in two monochrome X-ray CT method. However, since our developed CdTe imager can be detect five energy-bands at the same time, we can use multi-band analysis to decrease the least square error margin. We will be able to obtain more high separation in atomic number mapping in X-ray CT reconstructed image by using this system.

CdTe x-ray image sensor using a field emitter array

The authors have demonstrated the novel CdTe x-ray imaging device that consists of a Schottky CdTe diode and a 12×12 matrix-structured field emitter array (FEA). The Schottky CdTe diode was fabricated by depositing In on a Cl-doped p-type (π-type) CdTe substrate and Sb2S3 on the opposite side of the CdTe substrate. The matrix-structured FEA was fabricated by reactive ion etching and etch-back method. The output current was successfully detected by the recombination of holes with electrons from the FEA, and clearly depended on the x-ray intensity.

Carrier transportation and polarization properties in CdTe diode detectors

The carrier transportation properties of a P-intrinsic-N (PiN) type CdTe diode detector for radiation spectrography was evaluated under the non-polarized and polarized condition with high speed signal processing method for a practical photon-counting system. The rise-up time distribution in each energy region was obtained by our system in each operation condition. These results suggest that the polarization affects transportation speed of holes slower than electrons, because the rise-up time distribution in same detection efficiency of the polarization condition (passage of time 90 min at bias voltage 200 V), and the non-polarization condition with lower bias voltage (passage of time 1 min at bias voltage 50 V) shows obviously different tendency by energy region. We believe our new approach could give key information for analyzing the polarization phenomenon in CdTe diode detectors.

CdTe x-ray sensing driven by electron beam from field emitters

In this paper, a CdTe X-ray sensing device which consists of a CdTe pin diode and a field emitter is fabricated. The CdTe pin diode was fabricated by an excimer laser doping method, which was applied to form an n-type CdTe layer. An indium thin layer was evaporated on the p-type CdTe as a dopant material, and then an n-type CdTe layer was formed by irradiating a KrF laser to the dopant layer in a high-pressure Ar ambient. The field emitter used in this experiment was sputter-induced carbon nanoneedle field emitters. A positive bias voltage of ~200 V was applied to the n-region of the CdTe diode and output currents flowing were measured in the CdTe by supplying an electron beam on the p-region of the CdTe. The electron beam current supplied from the emitter was 10 muA. The output current is shown to be proportional to the X-ray tube current which is also proportional to the X-ray intensity. Also, output current is obtained only when the electron beam is irradiated

Digital signal processing for CdTe photon-counting X-ray sensor

Recently the practical X-ray measurement system is demanded energy distinction function with the high count rate and the high energy resolution used photon-counting X-ray sensor. Photon-counting CdTe semiconductor detectors have a high energy resolution in a low count rate at room temperature. However, the energy resolution is decreased by pile-up phenomenon in a high count rate. It is because that the photon counting sensor was used the signal-processing algorithm that the photon energy was estimated by integration of the output waveform from the CdTe detector. Moreover, the photon counting sensor is required to maintain the property of a high energy resolution even if the pile-up occurred. This paper purposes to maintain the high energy resolution by changing the signal-processing algorithm which derived the digital energy value from the pulse rise height of the output waveform generated the pile-up from the CdTe detector. As a result, the pulse rise time required to estimate the pulse rise size was shorter than 500ns. As the result of calculating energy spectrum by using this data, the FWHM of about 4keV (at 60keV) when the count rate of 3counts/60us in the pulse attenuation constant of 60μs was obtained (the pile-up is occurred in this condition). Furthermore, for confirmation of this signal processing in high count rate condition, we used white X-ray together with Am241 in order to measure energy spectrums in a high count rate. As a result of measurement energy spectrum in a high count rate, the FWHM was about 11keV (at 60keV) when the count rate of 500kcps.This result is indicated the possibility that the photon counting sensor has application for the high count rate imaging without decrease of the high energy resolution.

X-ray, gamma-ray detector/imager by CdTe semiconductor and its applications

Photon counting type X-ray, gamma-ray detector and imager were developed by using CdTe compound semiconductor. The detector / imager could be applied for practical application and we tried to apply material identificated X-ray CT. The imager has photon energy discriminate function and high linearity between number of incident photons and output counts. It make high contrast image for X-ray penetration image and material identification in X-ray computed tomography (CT) measurement.

Photon counting x-ray CT with 3D holograms by CdTe line sensor

The novel 3-D display system is required in the medical treatment field and non-destructive testing field. In these field, the X-ray CT system is used for obtaining 3-D information. However, there are no meaningful 3-D information in X-ray CT data, and there are also no practical 3-D display system. Therefore, in this paper, we propose an X-ray 3-D CT display system by combining a photon-counting X-ray CT system and a holographic image display system. The advantage of this system was demonstrated by comparing the holographic calculation time and recognizability of a reconstructed image.

Thermal Neutron Detection by CdTe Detector

Thermal neutron detector is developed by using Cadmium telluride (CdTe) semiconductor, due to large thermal neutron capture cross section of Cd. The developed detector demonstrated the occurrence of the 96 keV gamma ray emissions from 113Cd(n, γ) 114Cd reaction.