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arxiv: 2512.11126 · v2 · submitted 2025-12-11 · ⚛️ physics.ins-det

Experimental and Monte Carlo Simulation Studies to Investigate the Working Principle of Compact Nanodosimeters

Victor Merza , Aleksandr Bancer , Vladimir Bashkirov , Ana Belchior , Beata Brzozowska , Jo\~ao F. Canhoto , Piotr Gasik , Jaroslaw Grzyb
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Khaled Katmeh Marcin Pietrzak Antoni Ruci\'nski Reinhard Schulte
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Pith reviewed 2026-05-16 22:31 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords nanodosimetersion-impact ionizationsignal inductionlow-pressure propaneMonte Carlo simulationGeant4-DNAGarfield++radiation detectors
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The pith

Experiments confirm ion-impact ionizations as primary signal mechanism in compact nanodosimeters

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tests the core assumption behind compact nanodosimeters by building a single-cell detector with a grounded readout electrode that isolates ions from wall effects. High signal yields were measured in 1 mbar and 2 mbar propane gas when negative high voltage was applied to the cathode, indicating that positive ions ionize gas molecules as the main process for signal induction. Secondary electron emission from the cathode surface was noted as a possible secondary contribution. Monte Carlo simulations with Geant4-DNA and Garfield++ were used to model ion collection and multiplication. Verifying this mechanism matters because it supports the nm-equivalent spatial resolution needed for tracking ionization clusters in particle therapy, radiation protection, and space dosimetry.

Core claim

By covering the 1.5 mm cell hole with a grounded readout electrode containing a 0.8 mm hole, the setup prevents collected ions from interacting with the dielectric walls. High signal yields at low propane pressures show that ion-impact ionizations of gas molecules dominate signal formation, while ion-induced secondary electron emission from the cathode may also contribute. The Geant4-DNA and Garfield++ models reproduce the observed ion collection and multiplication behavior.

What carries the argument

Isolated single cell hole with 0.8 mm grounded readout electrode that separates ion-gas ionization from wall interactions.

Load-bearing premise

The grounded readout electrode with its 0.8 mm hole fully prevents collected ions from interacting with the cell hole walls.

What would settle it

A large drop in signal yield when the readout hole is enlarged or removed to allow ions to reach the cell walls would show that wall effects contribute substantially.

Figures

Figures reproduced from arXiv: 2512.11126 by Aleksandr Bancer, Ana Belchior, Antoni Ruci\'nski, Beata Brzozowska, Jaroslaw Grzyb, Jo\~ao F. Canhoto, Khaled Katmeh, Marcin Pietrzak, Piotr Gasik, Reinhard Schulte, Victor Merza, Vladimir Bashkirov.

Figure 1
Figure 1. Figure 1: Illustration of the working principle of state-of-the-art compact nanodosimeters based [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Top view of the detector interior attached to the lid of the low-pressure chamber. [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Schematic of the detector in the x–z plane, where the z-axis is normal to the dielectric plate and the x-axis is aligned with the alpha-particle beam axis. The sketch highlights the central axis of the circular hole in the dielectric plate and is superimposed with electric field streamlines generated by the cathode at –800 V and the anode, positioned at z = 23.5 mm (not shown), with a potential of 30 V. th… view at source ↗
Figure 4
Figure 4. Figure 4: Simplified Geant4 model of the experimental setup. The collimator is simplified, only [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Geant4-DNA simulated ICSD produced in the SV with a diameter of 3.09 mm for a [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Geant4-DNA simulated ionization density as a function of the radial distance of the [PITH_FULL_IMAGE:figures/full_fig_p010_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Mean measured ion arrival time as a function of the cathode voltage for the stated [PITH_FULL_IMAGE:figures/full_fig_p011_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Simulated electric field magnitude for different cathode voltages along the [PITH_FULL_IMAGE:figures/full_fig_p012_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Measured signal yields as a function of the cathode voltage for the stated propane gas [PITH_FULL_IMAGE:figures/full_fig_p013_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Signal creation probability per collected ion as a function of the cathode voltage for the [PITH_FULL_IMAGE:figures/full_fig_p014_10.png] view at source ↗
read the original abstract

In recent years, compact nanodosimetric detectors based on ion multiplication in low-pressure gas have been developed and gained attention in the scientific community. These detectors use strong electric fields to collect and multiply positive ions produced by the incident radiation in mm-sized cell holes in dielectric materials, achieving a nm-equivalent spatial resolution of the localization of ionization events, when scaled to liquid water at unit density. Their design assumes that ion-impact ionizations of gas molecules within the cell holes dominate signal formation, yet this assumption has lacked direct physical verification. Electron emission from the cell hole walls or the cathode due to ion-impact could also contribute, requiring alternative designs to optimize efficiency. To investigate the relative importance of the possible mechanisms, a nanodosimetric detector featuring a single cell hole with a diameter of 1.5 mm in a dielectric plate was developed. Ion collection and multiplication were achieved by applying a negative high voltage to the glass cathode 0.5 mm below the cell hole, assisted by a low drift field above the plate. A grounded readout electrode with a 0.8 mm hole covers the cell hole to prevent interactions of collected ions with the hole walls. High signal yields in 1 mbar and 2 mbar propane gas were observed and indicated that ion-impact ionizations of the gas molecules could indeed be the primary mechanism for signal induction. Ion-induced secondary electron emission from the cathode was identified as another potential contribution. The compact nanodosimeter setup was further modeled with Geant4-DNA and Garfield++ for deeper insight. The results of these studies are important for understanding and developing a new class of nanodosimeters with potential applications in particle therapy, radiation protection, space dosimetry, and particle physics.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript describes the design, experimental testing, and Monte Carlo modeling of a compact nanodosimeter with a single 1.5 mm diameter cell hole in a dielectric plate. Using propane at 1 mbar and 2 mbar, high signal yields were measured with a negative high voltage on the glass cathode 0.5 mm below the hole and a low drift field above, assisted by a grounded readout electrode with a 0.8 mm hole intended to isolate collected ions from wall interactions. The authors conclude that ion-impact ionizations of gas molecules are the primary signal mechanism, with possible additional contribution from ion-induced secondary electron emission from the cathode. The setup is simulated with Geant4-DNA and Garfield++.

Significance. If the experimental isolation holds, the work provides direct verification of the dominant signal-formation mechanism assumed in compact nanodosimeter designs, which is relevant for applications in particle therapy, radiation protection, space dosimetry, and particle physics. The combination of measurements at two pressures with two standard Monte Carlo packages offers moderate support for the primary-mechanism claim, though the absence of quantitative yields and error bars weakens the evidential weight.

major comments (1)
  1. [Abstract and Experimental Setup] The central claim that high signal yields demonstrate ion-impact ionization of gas molecules as the primary mechanism rests on the assumption that the grounded readout electrode with its 0.8 mm hole fully prevents collected ions from interacting with the cell hole walls (Abstract and Experimental Setup). The manuscript does not quantify the wall-hit fraction in the Garfield++ simulations under the operating voltages, 1.5 mm hole geometry, and 1–2 mbar propane pressures, where transverse diffusion or field fringing could allow ions to reach the dielectric walls and induce secondary electrons. This quantification is required to isolate the gas-ionization contribution.
minor comments (1)
  1. [Abstract] The abstract refers to 'high signal yields' without reporting numerical values, uncertainties, or the criteria used to attribute yields to gas ionization versus cathode emission.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed review and constructive feedback on our manuscript. We address the single major comment below and will revise the manuscript to incorporate the requested quantification.

read point-by-point responses

  1. Referee: [Abstract and Experimental Setup] The central claim that high signal yields demonstrate ion-impact ionization of gas molecules as the primary mechanism rests on the assumption that the grounded readout electrode with its 0.8 mm hole fully prevents collected ions from interacting with the cell hole walls (Abstract and Experimental Setup). The manuscript does not quantify the wall-hit fraction in the Garfield++ simulations under the operating voltages, 1.5 mm hole geometry, and 1–2 mbar propane pressures, where transverse diffusion or field fringing could allow ions to reach the dielectric walls and induce secondary electrons. This quantification is required to isolate the gas-ionization contribution.

    Authors: We agree that an explicit quantification of the wall-hit fraction is needed to strengthen the isolation of the gas-phase ion-impact ionization mechanism. The original manuscript describes the grounded readout electrode design as intended to minimize wall interactions but does not report the simulated fraction. In the revised version we will add Garfield++ results that calculate the wall-hit fraction for the 1.5 mm hole geometry, operating voltages, and 1–2 mbar propane pressures, including the effects of transverse diffusion and field fringing. This will allow a direct assessment of the contribution from gas-molecule ionizations versus possible wall-induced secondary electrons. revision: yes

Circularity Check

0 steps flagged

No significant circularity; claims rest on direct experiment and standard external simulations

full rationale

The paper reports experimental signal yields in 1-2 mbar propane and attributes them to ion-impact ionization based on the observed data and modeling with the independent, publicly available packages Geant4-DNA and Garfield++. No derivation chain, fitted parameter, or self-citation is used to generate the central claim; the 0.8 mm hole design is presented as an engineering choice whose effectiveness is tested by the measurements themselves rather than assumed by construction. The result is therefore self-contained against external benchmarks and does not reduce to its inputs.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The study relies on standard assumptions of gas ionization physics and the accuracy of Geant4-DNA and Garfield++ transport models; no new free parameters, ad-hoc axioms, or invented entities are introduced.

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Reference graph

Works this paper leans on

5 extracted references · 5 canonical work pages

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    URL:https://link.aps.org/doi/10.1103/PhysRev.169.263, doi:10. 1103/PhysRev.169.263. Vasi, F., Kempf, I., Besserer, J., Schneider, U., 2021. Fire: A compact nanodosime- ter detector based on ion amplification in gas. Nuclear Instruments and Meth- ods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 999, 165116....

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