Development of a High-Resolution, High-Dynamic-Range Charge Detector for Ion Beam Monitoring

A. Tiberio; C. Diaz; C. Pizzolotto; E. Berti; G. Martinez; G. Zampa; J. Casaus; J. Marin; L. Pacini; M. Scaringella

REVIEW 4 major objections 5 minor 18 references

Development of a High-Resolution, High-Dynamic-Range Charge Detector for Ion Beam Monitoring

T0 review · 4 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read A prototype silicon-photodiode charge detector identifies nuclei from atomic number 5 to 75 with resolution better than 0.3 charge units.

desk verdict A genuinely useful low-cost charge tagger whose headline resolution is probably inflated by a selection cut; still worth refereeing and, with a reanalysis, likely a solid instrument paper. read the letter →

arxiv 2412.13934 v1 pith:62PQZN25 submitted 2024-12-18 physics.ins-det astro-ph.IM

O. Adriani , E. Berti , P. Betti , J. Casaus , R. DAlessandro , S. Detti , C. Diaz , J. Marin

show 9 more authors

G. Martinez N. Mori L. Pacini C. Pizzolotto A. Tiberio M. Scaringella O. Starodubtsev G. Zampa N. Zampa

This is my paper · ORCID

classification physics.ins-detastro-ph.IM

keywords chargedetectorionbeammonitoringsiliconphotodiodesnuclearresolutionHiDRAASICdynamicrangetestsparticleidentification

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper reports the development of a charge detector for monitoring high-energy ion beams. The prototype uses six silicon photodiodes and a custom readout chip to measure the atomic number $Z$ of each passing nucleus. In beam tests, the second prototype achieved charge resolution better than 0.3 charge units for $Z$ from 5 to 75, with a dynamic range spanning roughly $Z=1$ to 80 and a linear response across the whole range. The authors stress that the analysis is simple enough for quasi-real-time online monitoring, unlike silicon-strip detectors that need complex position, angle, and velocity corrections. The central contribution is a low-cost, modular detector concept that can tag nuclei event-by-event during accelerator or space experiments.

What carries the argument

The load-bearing mechanism is direct ionization in the depleted volume of commercial PIN photodiodes: a passing nucleus deposits charge proportional to $Z^2$ in the roughly 220 $\mu$m depletion depth, and the HiDRA 2 readout chip, a space-oriented ASIC with automatic double gain, integrates this charge. The analysis uses the truncated mean of the six diode signals after requiring all six to agree within 1.5 charge units. Because the detector has no strip geometry, there is no charge-sharing between readout elements, which removes the need for per-strip equalization and for position-, angle-, velocity-, and time-dependent corrections. This combination produces the nearly flat resolution and the wide dynamic range the paper reports.

What would settle it

Measure the charge resolution with the six-diode consistency requirement relaxed from 1.5 charge units to, say, 3 charge units, using the same beam data. If the resolution at $Z=75$ degrades by more than a small amount, the quoted value below 0.3 $\Delta Z$ is partly a product of event selection rather than the detector itself.

Watch

Extended reading notes

Core claim

The central claim is that a detector made of fully depleted silicon photodiodes, read out by a double-gain charge-sensitive amplifier ASIC, can measure nuclear charge with high resolution over a very wide dynamic range without charge-sharing corrections. In the authors' tests, the second prototype, operated at 100 V bias and requiring all six photodiodes to agree within 1.5 charge units, produced Gaussian peaks for each nuclear species and a measured resolution below 0.3 $\Delta Z$ from $Z=5$ to $Z=75$. Linearity holds whether peak positions are read from local maxima or Gaussian fits. The detector can identify nuclei from $Z=1$ to $Z=80$, with low-$Z$ resolution limited mainly by the fitting procedure rather than by the sensor.

Load-bearing premise

The headline resolution assumes the analysis keeps only events in which all six photodiodes agree within 1.5 charge units; if this cut removes real signal fluctuations, the quoted resolution overstates what the detector achieves on all events.

Editorial extensions

If this is right

A beam monitor of this kind can report nuclear composition online, since the analysis is a simple truncation and consistency check rather than a track fit.
The detector covers $Z$ up to about 80, beyond the typical $Z\sim28$–30 range of microstrip readouts, allowing monitoring of heavy fragmented beams.
The modular matrix design, together with unpackaged diodes, would lower the material budget and reduce nuclear fragmentation inside the detector.
The same device can serve as a charge tagger inside larger experiments, where it requires no channel-to-channel equalization or time-dependent corrections.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The quoted resolution depends on a selection cut (all six diodes within 1.5 charge units) that keeps less than half of events; if this cut preferentially discards fluctuating signals, the true resolution at full efficiency may be worse. A straightforward check would be to recalculate resolution as the consistency threshold is relaxed.
The same detector concept could be adapted to thin, unpackaged diode matrices with faster readout to monitor accelerator beams at rates far above the current roughly 1 kHz ASIC limit.
With background subtraction and asymmetric peak fitting, the low-$Z$ range ($Z<5$) could likely match the high-$Z$ resolution, making the full dynamic-range claim of $Z=1$ to 80 testable in a unified way.
The linearity of the truncated-mean response suggests the device could be used to calibrate the charge response of other detectors online during mixed-ion beam tests.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Short version: this is a real detector paper with a genuinely useful new combination — cheap off-the-shelf PIN photodiodes plus the HiDRA2 ASIC — and beam test results that show a wide dynamic range and good linearity. The headline claim of <0.3 ΔZ resolution from Z=5 to 75, though, is likely optimistic because the six-of-six consistency cut in Section 4 throws away more than half the events and uses the same photodiode charges that go into the resolution histogram. That selection is a variance-reducing cut on the observable you're characterizing. The paper is upfront about the efficiency, but it never quantifies how much that cut improves the quoted width, and there are no error bars on any resolution point. So the quantitative headline is conditional, not as solid as the abstract suggests.

The strongest part is the engineering and the analysis speed: no charge sharing, no complicated calibrations, truncated mean is enough. That's a real advantage for beam monitoring, and the comparisons to silicon strip detectors are fair. The 2022 and 2023 beam tests give real data from HERD and AMS setups; the paper's account of the detector and the electronics is clear. The citation pattern looks appropriate — they cite the ASIC and CaloCube work and are not hiding prior art.

Soft spots beyond the selection cut: the quoted resolution is inconsistent between Section 5 ('better than 0.3') and the conclusions ('approximately 0.25'). Low-Z performance is explicitly not evaluated because of asymmetric distributions and missing background subtraction, yet the abstract still claims dynamic range down to Z=1. The authors are candid about this, but the abstract oversells. There's also no per-Z efficiency or uncertainty, so the first-to-second-prototype improvement is hard to judge. None of these are fatal — the detector concept is sound and the beam test is genuine — but they make the central numbers less persuasive than they could be.

Who should read it: detector developers working on beam tags, cosmic-ray charge measurement, or anyone considering photodiode-based charge detectors. It deserves a serious referee; the flaws are fixable in revision. I'd recommend sending for peer review, with the expectation that the authors should add a diode-splitting consistency check, error bars, and a resolution versus cut efficiency scan.

Referee Report

4 major / 5 minor

Summary. The paper reports the development and beam-test characterization of a charge detector for monitoring high-energy ion beams, built from six blinded silicon photodiodes read out by the HiDRA-2 ASIC. Two prototypes were tested at CERN SPS with fragmented lead beams: the first with four-of-six photodiode consistency and 40 V bias, the second with six-of-six consistency and 100 V bias. The central claim is that the second prototype achieves charge resolution better than 0.3 ΔZ for Z=5 to Z=75 and a dynamic range up to Z~80, with excellent linearity and fast quasi-real-time analysis. The paper also discusses further developments in sensor geometry and readout electronics.

Significance. If the central performance claim holds, the detector would be a simple, low-cost, high-dynamic-range beam monitor with a much simpler calibration and analysis chain than silicon microstrip charge detectors. The use of commercial photodiodes, existing space-qualified ASIC readout, and the demonstrated operation in real beam tests are concrete strengths. However, the quantitative resolution claim rests on an event selection that discards more than half of the events, and the paper provides no statistical uncertainties on the resolution points. The significance is therefore moderate: the detector concept is promising, but the headline number needs a more careful selection-bias study before it can be taken at face value.

major comments (4)

[Section 4, Section 5, Fig. 8] The quoted resolution better than 0.3 ΔZ for Z=5 to Z=75 is obtained from events passing a six-of-six consistency cut requiring all photodiodes to agree within 1.5 charge units, with a reported selection efficiency below 50%. Because the same photodiode signals are used both for the cut and for the truncated-mean histogram, the cut preferentially removes events with large fluctuation or Landau tails and can artificially narrow the measured peak width. The paper should quantify this effect by reporting the resolution as a function of the consistency window (e.g., six-of-six versus five-of-six versus four-of-six, or no consistency cut after the noise threshold), and should give per-Z selection efficiencies. As it stands, the headline resolution is not demonstrated to be an unbiased estimate of the inclusive detector resolution.
[Section 5, Figures 4-8] No statistical uncertainties are reported on the resolution or linearity points. The Gaussian-fit widths are plotted without error bars, making it impossible to judge whether the improvement from the first prototype (0.5 ΔZ) to the second prototype (0.3 ΔZ) is statistically significant, or whether the resolution is actually flat within errors as claimed. The authors should provide fit uncertainties and, where available, the number of events per peak.
[Section 5 and Section 7 (Conclusions)] There is a quantitative inconsistency in the stated resolution: Section 5 reports 'resolution better than 0.3 ΔZ from Z=5 to Z=75,' while the Conclusions state 'a linear Z resolution of approximately 0.25 ΔZ across the entire Z range.' These statements should be reconciled with the data in Figure 8, particularly given the caveat that the resolution for Z below 5 is not accurately evaluated and no background subtraction is implemented.
[Abstract and Section 5] The abstract claims a dynamic range capable of measuring nuclei with atomic numbers from 1 to 80, but quantitative resolution is only shown for Z=5 to Z=75. The low-Z region (Z<5) is explicitly described as not accurately evaluated, and no resolution points are presented for Z>75. The paper should distinguish detection capability from quantitatively characterized resolution, both in the abstract and in the conclusions.

minor comments (5)

[Section 4] The consistency requirement is described as 'a signal difference of less than 1.5 charge units,' but it is not specified whether this is a pairwise difference, a difference from the mean, or a maximum-minimum spread. Please define the exact criterion used.
[Section 5, Figures 4-8] The resolution definition used for the Gaussian width (sigma, FWHM, or standard deviation of the truncated-mean distribution) is not stated in the text or figure captions. Please define it explicitly in the captions or in the text.
[Section 2.2] The diode model is given as VTH2090 in Section 2.1 and as VTH20290 in Section 2.2. Please correct the typo.
[Section 4 and Section 6.2] The paper reports a selection efficiency below 50% from the six-of-six consistency cut and separately states in Section 6.2 that about 10% of events cannot be used due to CSA reset. These two inefficiencies should be clearly distinguished, and it should be stated explicitly whether the 50% figure already accounts for the reset losses.
[Section 5] The phrase 'no yellow area is present for failed/bad fits' in the description of Figure 4 is informal and potentially ambiguous; please state how failed fits are identified and shown.

Circularity Check

1 steps flagged · score 2.0 of 10

Mild selection-induced circularity: the headline charge resolution is measured on events selected by a six-of-six consistency cut using the same charge signals.

self definitional [Section 4 'Data analysis routine' and Section 5 'Test results', around Fig. 8]
"For the second prototype, we applied all the previously described selection criteria while increasing the requirement for the number of consistent PDs to six. This means that all diodes used in the detector must produce consistent signals ... Only events meeting these criteria were selected. While the efficiency of this selection method is currently less than 50% ... showcasing significant improvement with a resolution better than 0.3 ΔZ from Z=5 to Z=75. This enhancement is attributed to the higher bias voltage and refined event selection strategies implemented in the second prototype."

The quoted 'resolution better than 0.3 ΔZ' is the Gaussian width of the truncated-mean charge distribution after requiring all six photodiodes to agree within 1.5 charge units. That consistency requirement is a variance-reducing cut on exactly the per-diode charge values that subsequently enter the resolution histogram. Events with large Landau fluctuations or inter-diode discrepancies are preferentially discarded, and the reported efficiency is below 50%, so the surviving distribution is narrower than an inclusive measurement would be. The improvement from the first to the second prototype is therefore attributed in part to the selection itself, and the quoted detector resolution is conditional on the same observable used to define the event acceptance.

full rationale

The paper's calibration is anchored to an external standard: ADC-to-MIP conversion parameters are obtained from the carbon peak in the fragmented SPS beam, and MIP-to-Z follows from energy loss. The resolution values are read from Gaussian fits to measured peak widths, and no parameter is fitted to the target resolution values. There is no load-bearing self-citation chain or imported uniqueness theorem. The one legitimate near-circular element is the six-of-six consistency selection in Section 4: it uses the same photodiode charge measurements that later define the resolution histogram, and with efficiency below 50% it preferentially keeps events with small fluctuations. This makes the headline <0.3 ΔZ figure a conditional, selection-biased performance number rather than an unbiased inclusive resolution, but it is a statistical selection effect rather than a derivation-level equivalence-by-construction, so the circularity score is modest.

Assumptions & free parameters 4 free parameters · 4 assumptions · 0 invented entities

The central performance claims rest on calibration constants fitted to beam data, a consistency cut that selects events, and a small number of domain assumptions about signal uniformity and beam composition. No new physical entities are introduced.

free parameters (4)

ADC-to-MIP calibration constants = not quoted; obtained per diode from carbon peak
Section 4: conversion parameters from ADC to MIP were obtained for each diode by analysing the carbon peak in the fragmented SPS beam.
Consistency cut = 1.5 charge units
Section 4: required signal difference of less than 1.5 charge units among at least four (first prototype) or six (second) diodes; chosen by hand.
Noise threshold = 3 sigma
Section 4: signal amplitude evaluated above three times the noise threshold.
Operating bias voltage = 100 V for second prototype
Section 3: chosen to achieve full depletion; also 40V for the first prototype.

assumptions (4)

domain assumption The photodiode signal is proportional to the deposited charge and does not depend on particle trajectory or position within the diode.
Section 2.1 and 5: the detector relies on direct ionization in the depleted volume; no position-dependent corrections are applied.
domain assumption The known beam rigidity selection (A/Z) provides reliable identification of nuclear charge for calibration.
Section 5: beam composition with A/Z tuned using magnetic optics; used to set calibration and verify linearity.
domain assumption The truncated mean of the six diode signals removes Landau fluctuations and yields an unbiased estimate of the charge.
Section 4-5: truncated mean is used without a detailed simulation or demonstration of its bias.
domain assumption Full depletion is achieved and the depletion thickness is uniform at 100 V bias in the second prototype.
Section 3: operating at 100V with diodes selected for breakdown >100V; no direct verification of full depletion across the active area.

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Cite this review

Pith. "Pith review of Development of a High-Resolution, High-Dynamic-Range Charge Detector for Ion Beam Monitoring." pith.science (2026). https://pith.science/paper/62PQZN25

@misc{pith2026241213934,
  author       = {Pith},
  title        = {Pith review of: Development of a High-Resolution, High-Dynamic-Range Charge Detector for Ion Beam Monitoring},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/62PQZN25}},
  note         = {Machine review of arXiv:2412.13934}
}

read the original abstract

We present an innovative charge detector with high resolution and wide dynamic range designed to fulfill the requirements of a monitoring system for a high energy ion beam. The detector prototype, constructed using Si photodiodes and a custom readout electronics, underwent extensive testing during HERD and AMS beam tests at CERN SPS facilities. Initial testing showcased the detector's exceptional performance, emphasizing both high resolution and a dynamic range capable of measuring nuclei with atomic numbers ranging from 1 to 80. The prototype's compatibility with fast, quasi real-time data analysis qualifies it as an ideal candidate for online applications. This article presents the results from the testing phase of the prototype, highlighting its capabilities and performance. Ongoing detector development, potential applications, and future developments aimed at enhancing the detector's functionality and versatility are also discussed.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

18 extracted references · 17 canonical work pages

[1]

A. E. Berti, N. Mori, L. Pacini and O. Starodubtsev , The High Energy Cosmic -Radiation Detection HERD facility: a future space instrument for cosmic -ray detection and gamma- ray astronomy , in proceedings of 27th European Cosmic Ray Symposium - ECRS July 25- 29, 2022, Nijmegen, the Netherlands. PoS(ECRS)146

work page 2022
[2]

N. Mori, L. Pacini on behalf of the HERD collaboration, The High Energy Cosmic -Radiation Detection (HERD) facility for direct cosmic -ray measurements, in proceedings of 41st International Conference on High Energy physics - CHEP2022, July 6 -13 2022 Bologna, Italy PoS(ICHEP2022)123

work page 2022
[3]

https://home.cern/news/news/accelerators/accelerator-report-getting-lead-ions-ready-physics

work page
[4]

Betti et al., Photodiode Read-Out System for the Calorimeter of the Herd Experiment, Instruments 2022, 6(3), 33 [instruments6030033]

P. Betti et al., Photodiode Read-Out System for the Calorimeter of the Herd Experiment, Instruments 2022, 6(3), 33 [instruments6030033]

work page 2022
[5]

Y. W. Dong, Z. Quan, J. J. Wang, M. Xu, S. Albergo, F. Ambroglini, et al., Experimental verification of the HERD prototype at CERN SPS, Space Telescopes and Instrumentation 2016, UK: Ultraviolet to Gamma Ray, Edinburgh, 2016. DOI:10.1117/12.2231804

work page doi:10.1117/12.2231804 2016
[6]

2024 NIM A Volume 1064, 2024, 169346

Wei-Shuai Zhang et al., A novel charge reconstruction algorithm applied to the HERD prototype silicon charge detector . 2024 NIM A Volume 1064, 2024, 169346. DOI:10.1016/j.nima.2024.169346

arXiv 2024
[7]

O. Adriani et al ., The CALOCUBE project for a space based cosmic ray experiment: design, construction, and first performance of a high granularity calorimeter prototype 2019 JINST 14 P11004 DOI:10.1088/1748-0221/14/11/P11004

work page doi:10.1088/1748-0221/14/11/p11004 2019
[8]

Adriani et al., Development of the photo-diode subsystem for the HERD calorimeter double- readout, 2022 JINST 17 P09002

O. Adriani et al., Development of the photo-diode subsystem for the HERD calorimeter double- readout, 2022 JINST 17 P09002. DOI:10.1088/1748-0221/17/09/P09002

work page doi:10.1088/1748-0221/17/09/p09002 2022

Show all 18 references

[9]

https://www.datasheetcatalog.com/datasheets_pdf/V/T/H/2/VTH2090.shtml
[10]

https://cds.cern.ch/record/2318208/files/MikeJonesMSc_2.pdf pp.23-24
[11]

Pacini et al., Design and expected performances of the large acceptance calorimeter for the HERD space mission, PoS ICRC2021 (2021) 066

] L. Pacini et al., Design and expected performances of the large acceptance calorimeter for the HERD space mission, PoS ICRC2021 (2021) 066

2021
[12]

Bonvicini, G

V. Bonvicini, G. Orzan, G. Zampa and N. Zampa, A double -gain, large dynamic range front -end ASIC with A/D conversion for silicon detectors read-out, IEEE Trans. Nucl. Sci. 57 (2010) 2963

2010
[13]

https://www.weeroc.com/read_out_chips/skiroc-2a/
[14]

https://ideas.no/products/va32hdr14-3/ – 12
[15]

Oliva et al., The silicon charge detector of the high energy cosmic radiation detection facility

A. Oliva et al., The silicon charge detector of the high energy cosmic radiation detection facility . Proceedings of 38th International Cosmic Ray Conference - ICRC2023, Nagoya, Japan, PoS(ICRC2023)26
[16]

Adriani et al., The CaloCube calorimeter for high- energy cosmic- ray measurements in space: performance of a large-scale prototype, 2021 JINST 16 P10024 [arXiv:2110.01561]

O. Adriani et al., The CaloCube calorimeter for high- energy cosmic- ray measurements in space: performance of a large-scale prototype, 2021 JINST 16 P10024 [arXiv:2110.01561]

2021 arXiv
[17]

Alpat et al., Charge determination of nuclei with the AMS-02 silicon tracker 2005 NIM A Volume 540 Issue 1, Pages 121-130, DOI:10.1016/j.nima.2004.11.012

B. Alpat et al., Charge determination of nuclei with the AMS-02 silicon tracker 2005 NIM A Volume 540 Issue 1, Pages 121-130, DOI:10.1016/j.nima.2004.11.012

2005 doi
[18]

https://btf.lnf.infn.it/

Pith tools

Reviewed August 11, 2026 · model on record in the stance chip above.

[1] [1]

A. E. Berti, N. Mori, L. Pacini and O. Starodubtsev , The High Energy Cosmic -Radiation Detection HERD facility: a future space instrument for cosmic -ray detection and gamma- ray astronomy , in proceedings of 27th European Cosmic Ray Symposium - ECRS July 25- 29, 2022, Nijmegen, the Netherlands. PoS(ECRS)146

work page 2022

[2] [2]

N. Mori, L. Pacini on behalf of the HERD collaboration, The High Energy Cosmic -Radiation Detection (HERD) facility for direct cosmic -ray measurements, in proceedings of 41st International Conference on High Energy physics - CHEP2022, July 6 -13 2022 Bologna, Italy PoS(ICHEP2022)123

work page 2022

[3] [3]

https://home.cern/news/news/accelerators/accelerator-report-getting-lead-ions-ready-physics

work page

[4] [4]

Betti et al., Photodiode Read-Out System for the Calorimeter of the Herd Experiment, Instruments 2022, 6(3), 33 [instruments6030033]

P. Betti et al., Photodiode Read-Out System for the Calorimeter of the Herd Experiment, Instruments 2022, 6(3), 33 [instruments6030033]

work page 2022

[5] [5]

Y. W. Dong, Z. Quan, J. J. Wang, M. Xu, S. Albergo, F. Ambroglini, et al., Experimental verification of the HERD prototype at CERN SPS, Space Telescopes and Instrumentation 2016, UK: Ultraviolet to Gamma Ray, Edinburgh, 2016. DOI:10.1117/12.2231804

work page doi:10.1117/12.2231804 2016

[6] [6]

2024 NIM A Volume 1064, 2024, 169346

Wei-Shuai Zhang et al., A novel charge reconstruction algorithm applied to the HERD prototype silicon charge detector . 2024 NIM A Volume 1064, 2024, 169346. DOI:10.1016/j.nima.2024.169346

arXiv 2024

[7] [7]

O. Adriani et al ., The CALOCUBE project for a space based cosmic ray experiment: design, construction, and first performance of a high granularity calorimeter prototype 2019 JINST 14 P11004 DOI:10.1088/1748-0221/14/11/P11004

work page doi:10.1088/1748-0221/14/11/p11004 2019

[8] [8]

Adriani et al., Development of the photo-diode subsystem for the HERD calorimeter double- readout, 2022 JINST 17 P09002

O. Adriani et al., Development of the photo-diode subsystem for the HERD calorimeter double- readout, 2022 JINST 17 P09002. DOI:10.1088/1748-0221/17/09/P09002

work page doi:10.1088/1748-0221/17/09/p09002 2022