Nanodosimetry aims to predict the biological effectiveness of radiation through the spatial distribution of ionizations at the nanometer scale, corresponding to DNA dimensions. Direct measurement in tissue is impossible, so low-pressure gas is used, where millimeter volumes are equivalent to nanometer volumes in water thanks to density scaling theorems. Existing nanodosimeters, such as the ion counter, the LNL Startrack Counter, and the Jet Counter, are bulky and complex. Alongside this work on the archive are studies of ion transistors in nanopores, crystal-controlled proton beams, silicon detectors for particle counting, and quantum methods for amplifying weak signals. This work stands somewhat apart: it develops compact track detectors based on THGEM and RPC but with reversed polarity to collect positive ions, opening a path to miniaturization.
The detector consists of a dielectric plate with several holes (7 or 19) of diameter 0.6–0.8 mm arranged in a honeycomb pattern. Above the plate, a drift field is created; below it, a resistive glass cathode creates a strong field inside the holes. Alpha particles from an americium-241 source with an energy of 4.6 MeV pass through propane gas at a pressure of 1 mbar and ionize it. Positive ions drift toward the holes, where they initiate an avalanche, recorded as a pulse. Signals were digitized with a Picoscope 3206D oscilloscope and processed with a Savitzky–Golay filter and a peak-finding algorithm. To assess stability, dark counts and the temporal evolution of amplitudes were measured at different cathode potentials from −600 to −1000 V.
For plates D-1 (FR-4, 7 holes) and D-3 (acrylic, 7 holes), multiple pulses per alpha trigger were observed. The average pulse multiplicity reached 0.62 for D-1 and 1.92 for D-3 at certain voltages. Pulse arrival times clustered within 15 μs, consistent with ion drift simulations. However, the measured multiplicity is significantly lower than the expected average ionization cluster size (several tens), indicating low ion detection efficiency. Dielectric charging effects were observed with stabilization times ranging from 3.6 to 33 seconds. Repeated measurements showed a decrease in multiplicity over time due to cathode aging and the formation of polymer deposits from propane.
This work demonstrates a first step toward a compact nanodosimeter capable of measuring the distribution of ionization clusters in a single nanometer volume. Unlike neighboring works focusing on single holes or other principles, this is the first application of a group multi-hole structure to extract ions from one sensitive volume. This opens the way to miniaturization and potential clinical use. However, unresolved questions about secondary avalanches and inter-hole coupling require further research.
Future prototypes may include independent biasing and readout of each hole, which would reduce dead time and correlated avalanches. Using nitrogen instead of propane would reduce aging. Multilayer structures with additional electrodes would improve ion transport and collection efficiency. Measurements of ion-induced secondary electron emission yield are planned to understand signal mechanisms.
The technology could impact medical physics, radiation protection, and space dosimetry by providing a portable tool for assessing radiation quality.
It is necessary to map the sensitive volume for the multi-hole configuration, quantitatively separate independent and secondary pulses, and investigate long-term stability and methods for restoring the cathode surface.
The key unresolved problem in nanodosimetry is achieving high detection efficiency for single ions while maintaining compactness. This work highlights limitations related to dielectric charging and cathode aging and suggests directions to overcome them.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This paper presents a prototype of a compact nanodosimeter based on a multi-hole dielectric plate that detects positive ions from a nanometer-equivalent volume in propane at 1 mbar. Experiments with alpha particles from americium-241 showed multiple pulses per particle, indicating ion collection from a cluster. Despite moderate repeatability and charging effects, the principle of miniaturizing nanodosimetry has been demonstrated.
Where its strength is
The main strength is the first-time use of a grouped multi-hole structure to extract ions from a single sensitive volume, which paves the way for compact nanodosimeters. This is a concrete technical foundation on which further miniaturization and efficiency improvements can be built.
Where it could go next
Worth trying
Why this may matter
The development of compact nanodosimeters could make measurements of ionization distributions at the nanometer scale accessible in clinical settings, which is important for personalizing particle therapy and assessing radiation risks.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.53, against a usual 0.64. It looks like few have drilled nearby.
At a propane pressure of 1 mbar, a hole with a diameter of 0.8 mm corresponds to a volume in water with a diameter of about 8.4 nm, which is roughly the width of three turns of DNA.