Reference Detector Research Articles

Enhancing timing performance of heterostructures with double-sided readout

Objective.Heterostructured scintillators offer a promising solution to balance the sensitivity and timing in TOF-PET detectors. These scintillators utilize alternating layers of materials with complementary properties to optimize performance. However, the layering compromises time resolution due to light transport issues. This study explores double-sided readout-enabling improved light collection and Depth-of-Interaction (DOI) information retrieval-to mitigate this effect and enhance the timing capabilities of heterostructures.Approach.The time resolution and DOI performances of 3 × 3 × 20 mm3BGO&EJ232 heterostructures were assessed in a single and double-sided readout (SSR and DSR, respectively) configuration using high-frequency electronics.Main results.Selective analysis of photopeak events yielded a DOI resolution of 6.4 ± 0.04 mm. Notably, the Coincidence Time Resolution (CTR) improved from 262 ± 8 ps (SSR) to 174 ± 6 ps (DSR) when measured in coincidence with a fast reference detector. Additionally, symmetrical configuration of two identical heterostructures in coincidence was tested, yielding in DSR a CTR of 254 ± 8 ps for all photopeak events and 107 ± 5 ps for the fastest events.Significance.By using high-frequency double-sided readout, we could measure DOI resolution and improve the time resolution of heterostructures of up to 40%. The DOI information resulted intrinsically captured in the average between the timestamps of the two SiPMs, without requiring any further correction.

Evaluating the Transmission Type Reference Chamber for Small Field Dosimetry

AbstractTo assess the efficacy of a transmission‐type parallel plane reference chamber (T‐REF) for small‐field percentage depth dose (PDD) measurements using two high‐resolution detectors. The study utilizes microSilicon and microDiamond detectors for small‐field measurements, both with and without a T‐REF reference chamber. TrueBeam linear accelerator provides various photon energies (6X, 6XFFF, 10X, 10XFFF) for depth dose measurements. A sun‐nuclear 3D water tank is used to measure the PDD up to a depth of 15 cm. Analysis of the data includes a 1D gamma passing rate calculated using an in‐house MATLAB program. The study compares the PDD measurements obtained with and without the T‐REF. The T‐REF exhibits negligible beam perturbations across different field sizes and energies. The overall maximum mean PDD differences are 0.31 ± 0.16% for microSilicon and 0.33 ± 0.17% for microdiamond. The overall mean 1D gamma passing rate is 99.6 ± 0.2%. This study demonstrates that the T‐REF is a reliable and effective reference detector for small‐field radiation dosimetry.

Fluence measurement of monoenergetic neutrons from D(d,n) and T(d,n) reactions at the KRISS

A Cockcroft–Walton accelerator from High Voltage Engineering Europa BV was installed at the Korea Research Institute of Standards and Science in June 2022 to generate monoenergetic neutron fields. In this study, the fluences of monoenergetic neutron fields with energy peaks at 2.5, 2.8, and 3.2 MeV from the D(d,n) reaction and at 14.8 MeV from the T(d,n) reaction were measured. To measure neutron fluence, Bonner spheres with diameters of 17.78, 20.32, and 25.40 cm were placed at a distance of 1.50 m from the target. Additionally, a small size long counter was used separately as a neutron reference detector to monitor the stability of neutron production rate. For a deuteron beam current of 1 μA, the neutron fluences of monoenergetic neutron fields with energy peak at 2.5, 2.8, 3.2, and 14.8 MeV were determined to be 0.71 ± 0.03, 1.10 ± 0.04, 13.9 ± 0.5, and 258.0 ± 8.1 cm−2s−1μA−1, respectively.

Light yield measurement of the Ce3+ activated LuAG nano-powder garnet scintillating detector

This paper focuses on the characterization of nano-powder (NP) scintillator, specifically presenting preliminary results of the measurement of the light yield (LY) of a newly synthesized Lutetium Aluminum (LuAG) garnet phosphor NP scintillator, doped with 0.1% cerium. The scintillation light yield was measured using the comparative method. Considering the light-scattering and self-absorbing properties of powder scintillators, alpha particles from 241Am source were used for excitation instead of Gamma/X rays, while a Ce3+ activated LuAG single crystal (SC) was employed as the reference detector due to its well-established light yield. A photomultiplier tube (PMT) served as the photodetector, and signals were read out by a nuclear instrumentation chain. The results demonstrate that the newly prepared LuAG:Ce NP exhibits a light output that is approximately 90% of that of the single crystal reference. These findings highlight the promising potential of NP scintillators as a viable alternative to single crystals, especially in applications where the preference for powder scintillators is evident.

Characterization of the First Prototype of an Angular Independent Silicon Diode Array for Quality Assurance in Stereotactic Radiosurgery

Quality assurance (QA) ensures the accurate and safe delivery of radiation treatment. However, there are several challenges for advanced radiotherapy techniques, such as stereotactic radiosurgery (SRS), where substantial doses of radiation with multi-directional beams and variable dose rates are delivered to specific areas. Current dosimeters lack high precision, exhibiting issues with dependency on the angle of measurement and the dose rate. This study investigates the characterization of a two-dimensional edgeless silicon diode array for QA in SRS. This detector underwent evaluation of its dose linearity, percentage depth dose (PDD), output factors (OFs), dose rate variability, and angular dependence with megavoltage linear accelerator beams. The edgeless array demonstrated a linear response in the direct detection of MV therapeutic X-rays with sensitivity of 6.95 × 10−3 ± 2.3 × 10−5 Gy/nC, and the percentage differences for PDD and OF measurements were found to be within 2% compared to the reference detector. A dose per pulse dependence of ±2% was demonstrated across the range of 0.12 to 0.39 mGy/pulse. The angular dependence was within 2% variation for irradiation angles greater than 80° and smaller than 120°; however, a maximum of 4% variation was observed with some diodes for angles between 80° and 120°. The improved performance of the edgeless array is likely to overcome limitations of the current dosimeters for SRS QA by operating without the need of any corrections.

The response of radiation detectors in modulated fields for small targets

Intensity-modulated delivery techniques in radiotherapy are advanced methods that use the superposition of small fields to create complex dose distributions. These techniques result in intense gradients and inhomogeneous dose regions, making the dosimetry of composite fields challenging, especially when the sub-fields superposition does not restore charged particle equilibrium. This work aims to address the response of radiation detectors in non-equilibrium conditions. Two ionization chambers and a micro-diamond detector were irradiated using composite fields from VMAT plans with spherical targets with diameters ranging from 0.5 to 8 cm. The radiation detectors' response and the dose delivered by the VMAT plans were measured using a plastic scintillator detector and radiochromic film as reference detectors. It was observed that an under-response of the ionization chambers was up to 13% and an over-response of the micro-diamond detector was up to 2.5%. Additionally, output correction factors were derived and used to measure the absorbed dose in composite plans using the radiation detectors. The measured dose was compared with that measured with radiochromic film. A dose difference was found within radiochromic film uncertainties (<2.5%). The results of this work suggest that radiation detectors require output correction factors when non-equilibrium conditions persist in composite fields. However, a link between static and composite fields could not be established because the field size cannot be determined accurately.

Split-ring resonator with interdigital Split electrodes as detector for liquid and ion chromatography

The analysis of food and drugs as well as the monitoring of chemical processes and bioreactors by high-performance liquid chromatography and ion chromatography requires universal, cost-effective, and sensitive detectors. Therefore, this work presents a split-ring resonator that detects changes in the electrical and dielectric properties of the eluate from liquid chromatography or ion chromatography by monitoring the amplitude of the transmitted signal using an envelope detector. The used split-ring resonator consists of a simple printed circuit board featuring two microstrip lines. One is formed to a ring with interdigital split electrodes. The interdigital split electrodes forming the sensitive area significantly enhance the sensitivity to changes in relative permittivity, dielectric losses and electrical conductivity of the eluate In addition, the split-ring resonator is a small, inexpensive and easy-to-use detector that uses several dielectric parameters simultaneously for the measurement. Furthermore, the split-ring resonator measures these parameters at a significantly lower frequency than optical detectors and therefore measures different changes in frequency-dependent permittivity. For demonstrating feasibility of a split-ring resonator as a detector for high-performance liquid chromatography and ion chromatography, various anion and cation standards, basic and acidic amino acids, sugars, as well as sugar alcohols were separated and detected. A conductivity detector for ion chromatography and a refractive index detector for high-performance liquid chromatography were used as reference detectors.

Developments of a centimeter-level precise muometric wireless navigation system (MuWNS-V) and its first demonstration using directional information from tracking detectors

Various positioning techniques such as Wi-Fi positioning system have been proposed to use in situations where satellite navigation is unavailable. One such system, the muometric positioning system (muPS), was invented for navigation which operates in locations where even radio waves cannot reach such as underwater or underground. muPS takes advantage of a key feature of its probe, cosmic-ray muons, which travel straightforwardly at almost a speed of light in vacuum regardless of the matter they traverse. Similar to other positioning techniques, muPS is a technique to determine the position of a client’s muPS receiver within the coordinate defined by reference detectors. This can be achieved either by using time-of-flight (ToF) or angle of arrival (AoA) measurements. The latter configuration (AoA), called the Vector-muPS has recently been invented and the present paper describes the developments of the first prototype of a vector muometric wireless navigation system (MuWNS-V) with this new vector-muPS concept and its demonstration. With MuWNS-V, the reference tracker and the receiver ran wirelessly with fully independent readout systems, and a positioning accuracy of 3.9 cm (RMS) has been achieved. We also evaluated the outcome of measuring continuous indoor localization of a moving receiver with this prototype. Our results indicated that further improvements in positioning accuracy will be attainable by acquiring higher angular resolution of the reference trackers. It is anticipated that “sub-cm level” navigation will be possible for muPS which could be applied to many situations such as future autonomous mobile robot operations.

DOI- and TOF-capable PET array detector using double-ended light readout and stripline-based row and column electronic readout.

We investigate a highly multiplexing readout for depth-of-interaction (DOI) and time-of-flight PET detector consisting of an N×N crystals whose light outputs at the front and back ends are detected by using silicon photomultipliers (SiPM). The front N×N SiPM array is read by using a stripline (SL) configured to support discrimination of the row position of the signal-producing crystal. The back N×N SiPM array is similarly read by an SL for column discrimination. Hence, the detector has only four outputs. We built 4×4 and 8×8 detector modules (DM) by using 3.0×3.0×20 mm3 lutetium-yttrium oxyorthosilicates. The outputs were sampled and processed offline. For both DMs, crystal discrimination was successful. For the 4×4 DM, we obtained an average energy resolution (ER) of 14.1%, an average DOI resolution of 2.5 mm, a non DOI-corrected coincidence resolving time (CRT), measured in coincidence with a single-pixel reference detector, of about 495 ps. For the 8×8 DM, the average ER, average DOI resolution and average CRT were 16.4%, 2.9 mm, and 641 ps, respectively. We identified the intercrystal scattering as a probable cause for the CRT deterioration when the DM was increased from 4×4 to 8×8.

Scintillation and cherenkov photon counting detectors with analog silicon photomultipliers for TOF-PET

Objective. Standard signal processing approaches for scintillation detectors in positron emission tomography (PET) derive accurate estimates for 511 keV photon time of interaction and energy imparted to the detection media from aggregate characteristics of electronic pulse shapes. The ultimate realization of a scintillation detector for PET is one that provides a unique timestamp and position for each detected scintillation photon. Detectors with these capabilities enable advanced concepts for three-dimensional (3D) position and time of interaction estimation with methods that exploit the spatiotemporal arrival time kinetics of individual scintillation photons. Approach. In this work, we show that taking into consideration the temporal photon emission density of a scintillator, the channel density of an analog silicon photomultiplier (SiPM) array, and employing fast electronic readout with digital signal processing, a detector that counts and timestamps scintillation photons can be realized. To demonstrate this approach, a prototype detector was constructed, comprising multichannel electronic readout for a bismuth germanate (BGO) scintillator coupled to an SiPM array. Main Results. In proof-of-concept measurements with this detector, we were able to count and provide unique timestamps for 66% of all optical photons, where the remaining 34% (two-or-more-photon pulses) are also independently counted, but each photon bunch shares a common timestamp. We show this detector concept can implement 3D positioning of 511 keV photon interactions and thereby enable corrections for time of interaction estimators. The detector achieved 17.6% energy resolution at 511 keV and 237 ± 10 ps full-width-at-half-maximum coincidence time resolution (CTR) (fast spectral component) versus a reference detector. We outline the methodology, readout, and approach for achieving this detector capability in first-ever, proof-of-concept measurements for scintillation photon counting detector with analog silicon photomultipliers. Significance. The presented detector concept is a promising design for large area, high sensitivity TOF-PET detector modules that can implement advanced event positioning and time of interaction estimators, which could push state-of-the-art performance.

Dosimetry of ultra-high dose rate electron beams using thermoluminescence and optically stimulated luminescence detectors

Objective. The aim of this work is to investigate the dose rate dependence of thermoluminescence and optically stimulated luminescence detectors (TLDs and OSLDs) in a wide uniform ultra-high dose rate electron beam and demonstrate the potential use of TLDs and OSLDs to correct the ion recombination in air-filled ionization chambers. This study avoids previously reported complications related to the field size and homogeneity. Approach. Two types of OSLDs (BeO and Al2O3:C) and three types of TLDs (LiF:Mg,Ti, LiF:Mg,Cu,P, CaF2:Tm) were irradiated simultaneously in a uniform 16 MeV electron beam generated by a clinically decommissioned C-Arm LINAC, modified to deliver doses per pulse between 8.3 × 10−4 Gy and 1.255 Gy, corresponding to instantaneous dose rates between 2 × 102Gy s−1 and 3 × 105 Gy s−1. A prototype ultra-thin parallel plate ionization chamber was employed as reference detector. Main results. Reproducible results were achieved both at conventional (standard deviation of the data <2%) and at the highest dose per pulse (standard deviation of the data <4%). No trend in the dose rate response of the TLDs and OSLDs was observed in the investigated dose per pulse range. The Al2O3:C OSLD was found to be the most precise detector, with a standard deviation of the data <2% at all investigated dose rates and dose levels. Significance. The dose rate independence of the investigated TLDs and OSLDs make them good candidates for dosimetry at ultra-high dose rates, at least up to 3 × 105 Gy s−1. A dose rate independent method to measure the dose per pulse is proposed, which can be applied to characterize ultra-high dose rate electron beams and correct for ion recombination in ionization chambers.

Pushing the limit of BGO-based dual-ended Cherenkov PET detectors through photon transit time correction

Objective. The high production cost of commonly used lutetium-based fast scintillators and the development of silicon photomultipliers technology have made bismuth germanate (BGO) a promising candidate for time-of-flight positron emission tomography (TOF PET) detectors owing to its generation of prompt Cherenkov photons. However, using BGO as a hybrid scintillator is disadvantageous owing to its low photon statistics and distribution that does not conform well to a single Gaussian. To mitigate this, a proposal was made to increase the likelihood of detecting the first Cherenkov photons by positioning two photosensors in opposition at the entrance and exit faces of the scintillator and subsequently selectively picking an earlier timestamp. Nonetheless, the timing variation arising from the photon transit time remains affected by the entire length of the crystal, thereby presenting a possibility for further enhancement. Approach. In this study, we aimed to improve the timing performance of the dual-ended BGO Cherenkov TOF PET detector by capitalizing on the synergistic advantages of applying depth-of-interaction (DOI) information and crystal surface finishes or reflector properties. A dual-ended BGO detector was implemented using a 3 × 3 × 15 mm3 BGO crystal. Coincidence events were acquired against a 3 × 3 × 3 mm3 LYSO:Ce:Mg reference detector. The timing performance of the dual-ended BGO detectors was analyzed using conventionally proposed timestamp methods before and after DOI correction. Results. Through a DOI-based correction of photon transit time spread, we demonstrated a further improvement in the timing resolution of the BGO-based Cherenkov TOF PET detector utilizing a dual-ended detector configuration and adaptive arrival time pickoff. We achieved further improvements in timing resolution by correcting the offset spread induced by the fluctuation of timing signal rise time in the dual-ended detector. Significance. Although polishing the crystal surface was still favorable in terms of full-width-half-maximum value, incorporating DOI information from the unpolished crystal to compensate for photon travel time facilitated additional enhancement in the overall timing performance, thereby surpassing that achieved with the polished crystal.

Field output correction factors of small static field for IBA razor nanochamber

Purpose. The goal of this work is present results of field output factors (OF) using an IBA CC003 (Razor NanoChamber) and compare these results with PTW 60019 (MicroDiamond) and IBA Razor Diode. The experimental results for IBA CC003 were also compared with Monte Carlo (MC) Simulation, using Penelope and Ulysses programs. In addition, field output correction factors () for IBA CC003 were derived with three different methods: (1) using PTW 60019 and IBA Razor as reference detectors; (2) comparison between MC and experimental measurements; and (3) using only MC.Material and Methods. The beam collimation included in this study were (1) square field size between 10 × 10 and 0.5 × 0.5 cm2 defined by the MLC and jaws and (2) cones of different diameters. For IBA CC003 it was determined the polarity and ion collection efficiency correction factors in parallel and perpendicular orientation.Results. The results indicate (1) the variation of polarity effect with the field size is relevant for the determination of OF using IBA CC003, especially for parallel orientation; (2) there is no significant variation of the ion collection efficiency with the field size using IBA CC003 in parallel orientation; (3) OF differences between IBA CC003 and PTW 60019/IBA Razor, and experimental and MC results, increase with decreasing field size;The results indicate (1) using the first and second method, increase with decreasing field size, which can be related with the influence of the volume effect and (2) using the third method, decrease with decreasing field size, which can be explained by the perturbation effect.Conclusions. Our results demonstrate the need of applying for IBA CC003 for 1 cm, to compensate for volume averaging and perturbations effects.

Feasibility of using a transmission reference detector for beam commissioning measurements

Feasibility of using a transmission reference detector for beam commissioning measurements

Seven general radiography x-ray detectors with pixel sizes ranging from 175 to 76 μm: technical evaluation with the focus on orthopaedic imaging

Aim. Flat panel detectors with small pixel sizes general can potentially improve imaging performance in radiography applications requiring fine detail resolution. This study evaluated the imaging performance of seven detectors, covering a wide range of pixel sizes, in the frame of orthopaedic applications. Material and methods. Pixel sizes ranged from 175 (detector A175) to 76 μm (detector G76). Modulation transfer function (MTF) and detective quantum efficiency (DQE) were measured using International Electrotechnical Commission (IEC) RQA3 beam quality. Threshold contrast (C T) and a detectability index (d′) were measured at three air kerma/image levels. Rabbit shoulder images acquired at 60 kV, over five air kerma levels, were evaluated in a visual grading study for anatomical sharpness, image noise and overall diagnostic image quality by four radiologists. The detectors were compared to detector E124. Results. The 10% point of the MTF ranged from 3.21 to 4.80 mm−1, in going from detector A175 to detector G76. DQE(0.5 mm−1) measured at 2.38 μGy/image was 0.50 ± 0.05 for six detectors, but was higher for F100 at 0.62. High frequency DQE was superior for the smaller pixel detectors, however C T for 0.25 mm discs correlated best with DQE(0.5 mm−1). Correlation between C T and the detectability model was good (R 2 = 0.964). C T for 0.25 mm diameter discs was significantly higher for D150 and F100 compared to E124. The visual grading data revealed higher image quality ratings for detectors D125 and F100 compared to E124. An increase in air kerma was associated with improved perceived sharpness and overall quality score, independent of detector. Detectors B150, D125, F100 and G76, performed well in specific tests, however only F100 consistently outperformed the reference detector. Conclusion. Pixel size alone was not a reliable predictor of small detail detectability or even perceived sharpness in a visual grading analysis study.

Monte Carlo analyses and experimental investigation of the vanadium self-powered neutron detector in 60Co source and research pulsed reactor

As the online monitoring apparatus in the reactor, self-powered neutron detectors (SPNDs) have a great potential for development in nuclear energy. To further characterize the SPND response in the actual radiation field, some irradiation experiments and Monte Carlo analyses based on the 60Co gamma-rays source and a research pulsed reactor were performed. During the experiments, the current signals were measured with various reactor irradiation facilities. A series of experimental phenomena, such as the negative current effect of the gamma rays, shutdown attenuation current, and the difference in detector sensitivity, are described and theoretically explained by using a numerical model GEANT4-SPND, an in-house Monte Carlo toolkit for SPND simulation based on Geant4. The numerical model proves to be highly effective in restoring the experimental results for the detector response current, the signal prompt proportion, and the current trend. This work has not only validated the existing calculation method but also provided reference radiation field parameters and detector experimental data for the future development and verification of sensor models. Besides, the analyses results have provided some insights into the study of the mechanism and optimization of detector design.

Internal quantum efficiency of silicon photodetectors at ultraviolet wavelengths

We determine experimentally the internal quantum efficiency of a 3-element trap detector made of Hamamatsu S1337 photodiodes and of a predictable quantum efficient detector (PQED) over the wavelength range of 250–500 nm using an electrically calibrated pyroelectric radiometer as reference detector. The PQED is made of specially designed induced junction photodiodes, whose charge-carrier recombination losses are minimized. The determined internal quantum efficiency of PQED is always 1 or larger, whereas the 3-element trap detector has internal quantum efficiency smaller than 1 in the spectral range of 330–450 nm. This finding demonstrates the advantages of PQED photodiodes for studying the quantum yield due to impact ionization by charge carriers in the silicon lattice. For this purpose, we develop an extrapolation model for the charge-carrier recombination losses of the PQED, which allows us to separate the quantum yield from the measured internal quantum efficiency. Measurements of PQED spectral responsivity thus allow to determine the quantum yield in silicon, which can be further used for quantifying the charge-carrier recombination losses in the 3-element trap detector. Numerical values of the latter are from 6% to 2% in the spectral range from 250 nm to 380 nm. Finally, our results are encouraging for the aim of developing the PQED to a primary detector standard also at ultraviolet wavelengths.

Test-beam performance results of the FASTPIX sub-nanosecond CMOS pixel sensor demonstrator

Within the ATTRACT FASTPIX project, a monolithic pixel sensor demonstrator chip was developed in a modified 180 nm CMOS imaging process technology, targeting sub-nanosecond timing precision for single ionizing particles. It features a small collection electrode design on a 25 μm-thick epitaxial layer and contains 32 mini matrices of 68 hexagonal pixels each, with pixel pitches ranging from 8.66 to 20 μm. Four pixels are transmitting an analog output signal and 64 are transmitting binary hit information. Various design variations are explored, aiming at accelerating the charge collection and making the timing of the charge collection more uniform over the pixel area. Signal treatment of the analog waveforms, as well as reconstruction of digital position, time and charge information, is carried out off-chip. This contribution introduces the design of the sensor and readout system and presents performance results for various pixel designs achieved in recent test-beam measurements with external tracking and timing reference detectors. A time resolution below 150 ps is obtained at full efficiency for all pixel pitches.

FLASH Radiotherapy and the Use of Radiation Dosimeters.

Radiotherapy (RT) using ultra-high dose rate (UHDR) radiation, known as FLASH RT, has shown promising results in reducing normal tissue toxicity while maintaining tumor control. However, implementing FLASH RT in clinical settings presents technical challenges, including limited depth penetration and complex treatment planning. Monte Carlo (MC) simulation is a valuable tool for dose calculation in RT and has been investigated for optimizing FLASH RT. Various MC codes, such as EGSnrc, DOSXYZnrc, and Geant4, have been used to simulate dose distributions and optimize treatment plans. Accurate dosimetry is essential for FLASH RT, and radiation detectors play a crucial role in measuring dose delivery. Solid-state detectors, including diamond detectors such as microDiamond, have demonstrated linear responses and good agreement with reference detectors in UHDR and ultra-high dose per pulse (UHDPP) ranges. Ionization chambers are commonly used for dose measurement, and advancements have been made to address their response nonlinearities at UHDPP. Studies have proposed new calculation methods and empirical models for ion recombination in ionization chambers to improve their accuracy in FLASH RT. Additionally, strip-segmented ionization chamber arrays have shown potential for the experimental measurement of dose rate distribution in proton pencil beam scanning. Radiochromic films, such as GafchromicTM EBT3, have been used for absolute dose measurement and to validate MC simulation results in high-energy X-rays, triggering the FLASH effect. These films have been utilized to characterize ionization chambers and measure off-axis and depth dose distributions in FLASH RT. In conclusion, MC simulation provides accurate dose calculation and optimization for FLASH RT, while radiation detectors, including diamond detectors, ionization chambers, and radiochromic films, offer valuable tools for dosimetry in UHDR environments. Further research is needed to refine treatment planning techniques and improve detector performance to facilitate the widespread implementation of FLASH RT, potentially revolutionizing cancer treatment.

Microdosimetry

The interest in the application of microdosimetry for assessing the radiation quality of hadrontherapy fields has grown in the last two decades. The reference detector for microdosimetry is the tissue-equivalent proportional counter (TEPC). Novel types of microdosimeters have been developed by the Nuclear Measurement Laboratory of the Politecnico di Milano in collaboration with the INFN National Legnaro Laboratories. This work describes the main features of an avalanche confinement TEPC, capable of simulating sites down to 25 nm and a silicon telescope detector. The main dosimetric and microdosimetric quantities are also given and discussed in the Introduction for the sake of clarity.