Online program Overview Session: NSS-04

Abstract

Very-high-energy electrons delivered at ultra-high dose rates, are being investigated for their promise within radiotherapy to treat deep-seated tumours. VHEE FLASH radiotherapy research requires two major components; a real-time dosimeter that remains linear at the required dose-per-pulse, and an accelerator that is stable, biologically benchmarked, and suitable for in vivo studies. Investigations have been conducted at the Pulsed Energetic Electrons for Research (PEER) beamline of the ANSTO Australian Synchrotron to realise this reality. Utilising a 100 MeV electron linac, PEER provides irradiation fields comprised of 100 ps bunches with a 2 ns spacing, forming bunchtrains with average and instantaneous dose-rates as high as 10⁸ Gy/s and 10⁹ Gy/s, respectively. The MOSkin detector was tested for linearity with a dose-per-pulse as high as 23 Gy within 200 ns. During this work, EBT-XD radiochromic film was employed as a reference dosimeter, however, a dose-rate dependence of the film was discovered. This was confirmed with another experiment which allowed calculation of a correction factor, enabling use of the film as an independent measurement of dose. Three cell lines (A549, T98G, and MDCK) were irradiated utilising real-time dosimetry, and mouse cadavers were irradiated to assess the feasibility of small animal experiments. These results support PEER as being suitable for future in vivo VHEE FLASH research.

Abstract

This work investigates the feasibility of using the ALPIDE pixelated detector for two-dimensional
microdosimetry applications in proton therapy. The detector offers several advantages for
microdosimetry, including low noise, fast readout capability, flexible spatial sampling, and very
high spatial resolution. Detailed Geant4 simulations were developed to model an experimental
setup using an 80 MeV proton beam passing through different aluminium thicknesses. A strong
agreement was observed between the responses of the ALPIDE detector and the SOI
microdosimeter, demonstrating the capability of ALPIDE to accurately characterise LET
distributions in proton radiation fields. In addition, the proposed calibration approach showed that
the cluster size measured by the ALPIDE detector can be reliably converted to LET in silicon.
Thanks to its pixelated architecture, arbitrary groups of pixels can be selected and analysed,
enabling high-resolution two-dimensional LET mapping of complex radiation fields. These results
demonstrate the strong potential of the ALPIDE detector as a versatile and cost-effective tool for
advanced microdosimetry and proton beam LET_d characterisation.

Abstract

Neutrons produced around particle accelerators are a major concern for radiation protection in research, medical, and industrial facilities due to their contribution to occupational exposure, patient dose, and material activation. Accurate characterisation of neutron fields is therefore essential, but conventional techniques such as activation foils, Bonner sphere systems, and solid-state nuclear track detectors are limited by their lack of real-time capability.  In this work, we present the AlphaBeast, a CMOS-based detector designed for real-time monitoring of thermal and fast neutrons. This sensor has been designed as an electronic alternative to solid-state track detectors, using polyethene and 10B converters for fast and thermal neutron detection with on-chip discrimination thresholds. The system was calibrated using the irradiation facilities available at the Institut Pluridisciplinaire Hubert Curien in Strasbourg, France. A GATE/Geant4 Monte Carlo model was developed to simulate the detector response and optimise its performance. The AlphaBeast sensor was then tested in various mixed radiation fields, including radiotherapy rooms and accelerator casemates. Experimental results show good agreement with simulations and demonstrate its potential for real-time neutron monitoring in particle accelerator facilities.

Abstract

Fully depleted silicon pnCCD sensors are used for X-ray spectroscopy in applications ranging from X-ray astronomy to synchrotron radiation sources and free-electron lasers, due to their outstanding capabilities, such as high energy resolution, low electronic noise and excellent quantum efficiency. At HLL, a new series of pnCCD sensors with a 36 μm pixel size has been fabricated to investigate the performance of small-pixel pnCCD devices. Applications requiring high spatial resolution can benefit from smaller pixel sizes, utilizing position reconstruction based on charge sharing. This contribution focuses on the systematic comparison of different designs within this pnCCD production run. The investigated sensors include devices based on our standard JFET amplifier, as well as variants with modified readout anodes, different options for the biasing of the MOS structures between the p-registers, and an option for a sensor design with self-aligned channel guide implants. Since the devices share the same basic geometry and sensor thickness, their comparison allows design-dependent effects on the detector performance to be directly assessed, while also exploring possible simplifications of the fabrication process and the overall detector system. For this purpose, the sensor variants are tested under comparable operating conditions using a newly developed experimental setup at HLL. The sensors are read out in a column-parallel architecture using the VERITAS 2.1 ASIC. Their spectral performance is evaluated in terms of noise behavior, gain uniformity, charge transfer inefficiency, and energy resolution. The observed performance differences between the variants will be discussed as a basis for identifying optimization paths for future pnCCD sensor designs.

Abstract

A prototype high-purity germanium (HPGe) double-sided strip detector has been developed to maintain high energy resolution and high throughput at count rates relevant to MHz-rate gamma-ray spectroscopy and imaging. Conventional HPGe detectors provide excellent energy resolution but suffer from throughput loss and resolution degradation at elevated count rates, limiting their use in applications such as beam diagnostics, nuclear decommissioning, medical imaging, and prompt spectroscopy of superheavy elements.

This work presents the design, fabrication, and characterization of fine-pitch HPGe double-sided strip detectors developed for high-rate spectroscopy and imaging. A 0.5 mm strip pitch detector geometry was selected using analytical calculations and numerical simulations of efficiency, charge collection, throughput, timing, energy resolution, and position resolution. This prototype demonstrated an energy resolution of 1.8 keV FWHM at 662 keV under low-rate conditions, consistent with predicted performance, and has now undergone additional characterization at higher rates. Extensive characterization has also been performed on 1.16 mm-pitch HPGe strip detectors, providing a broader experimental basis for evaluating fabrication yield, leakage current, strip-to-strip uniformity, charge sharing, charge loss, and spectroscopic performance.

Results from both the 1.16 mm-pitch and 0.5 mm-pitch detectors will be presented. Energy resolution and throughput are evaluated as functions of shaping time, strip geometry, and incident count rate. These results demonstrate progress toward fine-pitch HPGe detector systems capable of high-resolution spectroscopy, three-dimensional position sensitivity, and sustained performance in high-rate environments.

Abstract

Direct electron detectors for transmission electron microscopy have achieved high spatial resolution, while quantitative imaging of fast dynamic processes remains limited by temporal performance. The EDET80k system is a DEPFET-based direct electron detector developed for time-resolved transmission electron microscopy with full-frame rates up to 80 kHz for a 1 MPixel detector consisting of four 512 × 512 pixel arrays with 60 µm pixel pitch. The detector employs parallel rolling-shutter readout with 100 ns row timing for high-speed burst acquisition. 
To enable dynamic imaging studies with EDET80k, high-speed acquisition modes and a synchronized optical setup are investigated. The detector sequencing framework supports configurable operation modes tailored to the intended measurement conditions. Full-frame and region-of-interest (window) acquisition modes are implemented and verified in digital test benches. Standard full-frame operation provides frame times of approximately 12.8 µs, while windowed acquisition enables frame times down to 3.2 µs and below.
To investigate detector behavior under dynamic imaging conditions, a synchronized optical setup with pulsed illumination and structured moving targets is developed to emulate transmission electron microscopy bright-field imaging conditions. Initial dynamic imaging measurements are performed to investigate frame-to-frame motion visibility under microsecond frame times and varying illumination conditions. The presented approach establishes the basis for proof-of-concept time-resolved dynamic imaging with EDET80k.