There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

J. Appl. Cryst.の発刊に際して

The ability of dual- and multi-energy CT to differentiate materials of different effective atomic numbers makes possible several new and clinically relevant CT applications.

Dual- and Multi-Energy CT: Principles, Technical Approaches, and Clinical Applications

This review (over 380 references) summarizes metal–organic frameworks (MOFs), Materials Institute Lavoisier (MILs), iso-reticular metal–organic frameworks (IR-MOFs), porous coordination networks (PCNs), zeolitic metal–organic frameworks (ZMOFs) and porous coordination polymers (PCPs) with selected examples of their structures, concepts for linkers, syntheses, post-synthesis modifications, metal nanoparticle formations in MOFs, porosity and zeolitic behavior for applications in gas storage for hydrogen, carbon dioxide, methane and applications in conductivity, luminescence and catalysis.

MOFs, MILs and more: concepts, properties and applications for porous coordination networks (PCNs)

Photon counting detectors (PCDs) with energy discrimination capabilities have been developed for medical x-ray computed tomography (CT) and x-ray (XR) imaging. Using detection mechanisms that are completely different from the current energy integrating detectors and measuring the material information of the object to be imaged, these PCDs have the potential not only to improve the current CT and XR images, such as dose reduction, but also to open revolutionary novel applications such as molecular CT and XR imaging. The performance of PCDs is not flawless, however, and it seems extremely challenging to develop PCDs with close to ideal characteristics. In this paper, the authors offer our vision for the future of PCD-CT and PCD-XR with the review of the current status and the prediction of (1) detector technologies, (2) imaging technologies, (3) system technologies, and (4) potential clinical benefits with PCDs.

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Vision 20/20: Single photon counting x-ray detectors in medical imaging

Polycrystalline CdTe thick films were grown by MBE technique with thicknesses up to 220 μm and growth rates up to 10 μm/h. The growth was performed on both, thermally oxidized silicon wafers and the Medipix2 ASIC [1]. We determined the mostly promising growth temperatures and show that the growth process is suitable to the Medipix2 readout electronics. For the first time, X-ray images with directly deposited CdTe were obtained. These first images show a high spatial resolution, demonstrating the high potential of future application of CdTe sensor films, directly deposited on readout-electronics. The detector properties of the films are characterized by electrical measurements and detector measurements.

High resolution x-ray imaging detector based on polycrystalline CdTe thick films

Currently, there is a great interest in the research and development of SrI 2 :Eu2+ scintillating crystals The high light yield, high density (46 g/cm3) and high effective atomic number (494) make the Eu2+-activated SrI 2 suitable for use as x-ray and gamma ray detector SrI 2 :Eu2+-single crystals were grown with the vertical Bridgman technique in silica ampoules to prevent melt hydration and oxygen contamination during the crystal growth For measurements, crystals were hermetically encapsulated in aluminum containers with quartz glass optical windows The radioluminescence spectra of the SrI 2 :Eu2+-samples show maximum at 431 nm and 432 nm for the 5% and 6% dopant concentrations respectively The light yield of the bulk samples was up to 80 000 photons/MeV and up to 119 000 photons/MeV for a 360 µm sample integrated in an x-ray imaging setup

Development of SrI 2 scintillators for spectroscopy and x-ray imaging applications

Impedance or admittance spectroscopy has been shown to be a very convenient tool for the investigation of deep levels in semiconductor junctions. At constant temperature a frequency sweep is performed. After that the impedance signal is analysed by a regularization method based on Tikhonov regularization in order to obtain the thermal relaxation times of the deep levels present in the junction. The high resolution of the regularization method in comparison to conventional techniques is demonstrated using simulated data. The temperature dependence of the thermal relaxation times provides information about the properties of the deep levels such as activation energy or capture cross section. Two donor levels with activation energies dE1 =0.58 eV and dE2 =0.68 eV are observed in our detector diodes. It can be shown that the concentration of level 2 is increased after irradiation.

Analysis of Deep Levels in GaAs Detector Diodes Using Impedance Spectroscopy

The FMF is developing gamma ray detectors with Coplanar Grid (CPG) configuration based on (Cd,Zn)Te. The work is focused on the crystal growth of detector material as well as the development of read-out electronics and data acquisition systems (GMCA). In order to increase the active detector volume, several CPG detectors are stacked back to back.

Coincidence measurements and long-term stability analysis with stacked (Cd,Zn)Te Coplanar Grid detectors

Nowadays, the detection of backscatter X-rays has become an essential part of road security scanners, where individuals are at risk of an accidental exposure to the pulsed photon radiation fields generated by the devices that implement this technique. Dose to soft-tissue measurements of a pulsed radiation field generated by a commercial cargo X-ray backscattering device are presented using a Timepix3 detector. To accurately estimate the imparted dose, the energy spectrum of a backscattering cargo scanner is measured with a thick CdZnTe hybrid semiconductor pixel detector. The deconvolution of this measured spectrum is performed and the contributions to the dose are calculated by means of the mass energy-absorption coefficients for soft-tissue. This methodology was assessed through a Monte-Carlo simulation, together with verification measurements using thermoluminescent detectors (TLDs) as a standard dosimetry system. Measurements of direct irradiation, for a 30 s scan with the device at 2 m from the detector, yielded a dose of (4.9 ± 0.7) μGy and (3.6 ± 0.3) μGy for the Timepix3 and TLDs, respectively. In a simulated cargo environment, with the detector behind a 1 mm thick steel wall, 30 s scan time, and 2 m source to detector distance, the dose measured by the Timepix3 was (1.7 ± 0.1) μGy, while for the TLDs (1.4 ± 0.6) μGy, showing that the proposed methodology has a similar response as compared to a standard dosimetry system.

Michael Fiederle

Papers

High resolution x-ray imaging detector based on polycrystalline CdTe thick films

Development of SrI 2 scintillators for spectroscopy and x-ray imaging applications

Analysis of Deep Levels in GaAs Detector Diodes Using Impedance Spectroscopy

Coincidence measurements and long-term stability analysis with stacked (Cd,Zn)Te Coplanar Grid detectors

Dose estimation in X-ray backscatter imaging with Timepix3 and TLD detectors