Calibration of a modular trap detector system towards a new realisation of the luminous intensity unit

A modular photometric trap detector system has recently been developed at Physikalisch-Technische Bundesanstalt (PTB). All parts of the detector are now completely calibrated. The new planned traceability chain for the realisation of luminous intensity unit can therefore be established for the first time. This contribution shows the results of the individual calibration steps including the associated measurement uncertainties and correlations. A major part of the calibrations along the traceability chain is done at the upgraded measurement setup TULIP (TUnable Lasers In Photometry). The improvements of the TULIP setup are presented and the effects on the measurement uncertainty are shown. The result of the first complete calibration according to the new traceability chain is compared to previous calibration results both in terms of spectral irradiance responsivity and luminous responsivity. The further steps required towards implementing the new traceability chain and the possible implications are discussed.

HEXITEC 2 × 2 tiled hard X-ray spectroscopic imaging detector system

HEXITEC is a spectroscopic imaging X-ray detector technology developed at the STFC Rutherford Appleton Laboratory for X-ray and γ-ray spectroscopic imaging applications. Each module has 80 × 80 pixels on a 250 μm pixel pitch, and has been implemented successfully in a number of applications. This paper presents the HEXITEC 2 × 2 detector system, a tiled array of 4 HEXITEC modules read out simultaneously, which provides an active area of 16 cm2. Systems have been produced using 1 mm thick Cadmium Telluride (CdTe) and 2 mm thick Cadmium Zinc Telluride (CdZnTe) sensor material. In this paper the system and data processing methods are presented, and the performance of the systems are evaluated. The detectors were energy calibrated using an 241Am sealed source. Three types of charge sharing correction were applied to the data-charge sharing addition (CSA), charge sharing discrimination (CSD), and energy curve correction (ECC) which compensates for energy lost in the inter-pixel region. ECC recovers an additional 34 % of counts in the 59.5 keV peak in CdTe compared to the use of CSD; an important improvement for photon-starved applications. Due to the high frame rate of the camera system (6.3 kHz) an additional End of Frame (EOF) correction was also applied to 6.0 % of events to correct for signals that were readout whilst the signal was still forming. After correction, both detector materials were found to have excellent spectroscopic performance with a mean energy resolution (FWHM) of 1.17 keV and 1.16 keV for CdZnTe and CdTe respectively. These results successfully demonstrate the ability to construct tiled arrays of HEXITEC modules to provide larger imaging areas.

High-Precision X-ray Total Scattering Measurements Using a High-Accuracy Detector System

The total scattering method, which is based on measurements of both Bragg and diffuse scattering on an equal basis, has been still challenging even by means of synchrotron X-rays. This is because such measurements require a wide coverage in scattering vector Q, high Q resolution, and a wide dynamic range for X-ray detectors. There is a trade-off relationship between the coverage and resolution in Q, whereas the dynamic range is defined by differences in X-ray response between detector channels (X-ray response non-uniformity: XRNU). XRNU is one of the systematic errors for individual channels, while it appears to be a random error for different channels. In the present study, taking advantage of the randomness, the true sensitivity for each channel has been statistically estimated. Results indicate that the dynamic range of microstrip modules (MYTHEN, Dectris, Baden-Daettwil, Switzerland), which have been assembled for a total scattering measurement system (OHGI), has been successfully restored from 104 to 106. Furthermore, the correction algorithm has been optimized to increase time efficiencies. As a result, the correcting time has been reduced from half a day to half an hour, which enables on-demand correction for XRNU according to experimental settings. High-precision X-ray total scattering measurements, which has been achieved by a high-accuracy detector system, have demonstrated valence density studies from powder and PDF studies for atomic displacement parameters.

Bias-voltage dependent operational characteristics of a fully spectroscopic pixelated cadmium telluride detector system within an experimental benchtop x-ray fluorescence imaging setup

Commercially available fully spectroscopic pixelated cadmium telluride (CdTe) detector systems have been adopted lately for benchtop x-ray fluorescence (XRF) imaging/computed tomography (XFCT) of objects containing metal nanoprobes such as gold nanoparticles (GNPs). To date, however, some important characteristics of such detector systems under typical operating conditions of benchtop XRF/XFCT imaging systems are not well known. One important but poorly studied characteristic is the effect of detector bias-voltage on photon counting efficiency, energy resolution, and the resulting material detection limit. In this work, therefore, we investigated these characteristics for a commercial pixelated detector system adopting a 1-mm-thick CdTe sensor (0.25-mm pixel-pitch), known as HEXITEC, incorporated into an experimental benchtop cone-beam XFCT system with parallel-hole detector collimation. The detector system, operated at different bias-voltages, was used to acquire the gold XRF/Compton spectra from 1.0 wt% GNP-loaded phantom irradiated with 125 kVp x-rays filtered by 1.8-mm Tin. At each bias-voltage, the gold XRF signal, and the full-width-at-half-maximum at gold Kα 2 XRF peak (∼67 keV) provided photon counting efficiency and energy resolution, respectively. Under the current experimental conditions, the detector photon counting efficiency and energy resolution improved with increasing bias-voltage by ∼41 and ∼29% at −300V; ∼54 and ∼35% at −500V, respectively, when compared to those at −100V. Consequently, the GNP detection limit improved by ∼26% at −300V and ∼30% at −500V. Furthermore, the homogeneity of per-pixel energy resolution within the collimated detector area improved by ∼34% at −300V and ∼54% at −500V. These results suggested the gradual improvements in the detector performance with increasing bias-voltage up to −500V. However, at and beyond −550V, there were no discernible improvements in photon counting efficiency and energy resolution. Thus, the bias-voltage range of −500 to −550V was found optimal under the current experimental conditions that are considered typical of benchtop XRF/XFCT imaging tasks.

Design of a Differential Safety Mechanism (DSM) Dedicated to the NSW Micromegas Wedges

The New Small Wheel Micromegas detector system for the Upgrade of ATLAS Muon Spectrometer is in the phase of integration and commissioning at the Laboratories BB5 and Building 191 at CERN respectively. In this framework, the produced modules are evaluated and tested at a Cosmic Ray Stand or at their final position on New Small Wheel. Providing gas mixture to the Micromegas Wedges, the static gauge pressure inside the detector’s layers must be kept below a nominal value around 3 mbar. Pressures above 10 mbar, due several reasons or gas line blocking, could cause serious damages in the detectors. In this work we describe the principle of operation and the design of a low cost intelligent unit, the “Differential Safety Mechanism”, dedicated to protect the Micromegas Wedges against unexpected slow or sudden increase of the static gauge pressure. The internal detailed structure, the simulation and the prototype tests of the DSM are presented analytically in this work.

High-Resolution Distributed Radiation Detector System Assisted by Intelligent Image Recognition

With the development of machine learning and image recognition technology, the detector system tends to be standardized and intelligent. However, large numbers of distributed radiation detectors connected to the power grid will bring huge uncertainty to the operation of the power grid and even cause certain interference. The monitoring system of the distributed radiation detectors can control the running status of the distributed photoelectric detection system in real-time and guarantee the safe and stable operation of the detector system. This article proposes an improved genetic detector system to avoid “blind spots” in the radiation detector monitoring based on the characteristics of photovoltaic (PV) arrays, which are considered as individual pixels, and then the reliability of the monitoring is ensured by the monitoring coverage of these pixels by the detector nodes. The performance of the radiation detector monitoring is restored by activating those spare nodes with sufficient energy to replace those that fail, ensuring that the distributed detection system can be monitored in a timely and efficient manner at all times. The simulation results confirm the reasonable validity of the algorithm.

GAMMA-RAY BURSTS: A PERSONAL VIEW

The first observations in gamma-ray astronomy were made in the late 1960's, primarily by balloon-borne observations. In the early 1970's, gamma-ray bursts were discovered, completely by accident, by satellites looking for man-made nuclear explosions in space. The celestial nature of these events were soon confirmed by other satellites. The first large detector system designed for cosmic gamma-ray bursts observations was the BATSE instrument on the Compton Gamma-Ray Observatory. Some of the details of the instrumentation onboard ballons and satellites and the gamma-ray bursts observational properties they determined are presented.