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arxiv: 2606.30169 · v1 · pith:WWMKDH7Fnew · submitted 2026-06-29 · 🌌 astro-ph.IM · physics.ins-det

Radiation effects and noise evolution in NewAthena WFI flight-production sensors

Valentin Emberger , Johannes M\"uller-Seidlitz , Luisa Ostler , Wolfgang Treberer-Treberspurg , Robert Andritschke , Annika Behrens , G\"unter Hauser , Peter Lechner
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Astrid Mayr Leonie Sommer
This is my paper

Pith reviewed 2026-06-30 03:50 UTC · model grok-4.3

classification 🌌 astro-ph.IM physics.ins-det
keywords radiation effectsDEPFET sensorsNewAthenareadout noisedark currentproton irradiationX-ray detectors
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The pith

Flight-production DEPFET sensors show increased readout noise and dark current after proton irradiation matching NewAthena mission dose.

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

This paper tests how radiation affects DEPFET sensors built for the Wide Field Imager on NewAthena. A flight-production 64x64-pixel sensor was exposed to 62.4 MeV protons while kept biased and at 213 K to match the expected total non-ionizing dose, with a separate test using X-rays for total ionizing dose. Changes in readout noise, dark current, and threshold voltage were recorded along with their temperature dependence and compared against earlier pre-flight sensor data. The results indicate what operating temperature will be needed to preserve the low noise required for the instrument's energy resolution through the end of the mission.

Core claim

After proton irradiation of a flight-production DEPFET sensor to a total dose equivalent to 2.6 · 10^9 10-MeV-protons/cm² and separate 15 Gy TID exposure, both performed while the device remained fully biased and operated at the nominal 213 K, measurable increases occurred in readout noise, dark current, and threshold voltage; temperature dependence and short-term annealing were also quantified, with direct comparison to prior pre-flight sensor results informing adjustments to operating temperature and projections of end-of-life performance.

What carries the argument

Post-irradiation measurements of readout noise, dark current, and threshold voltage performed on biased and operating flight-production DEPFET modules at controlled temperature.

If this is right

  • A lower operating temperature than 213 K may be required to offset the rise in dark current and keep readout noise near the beginning-of-life target.
  • End-of-life energy resolution could degrade unless temperature is adjusted to compensate for the observed radiation effects.
  • Short-term annealing behavior at low temperature provides data on whether noise recovers between periods of high particle flux.
  • Consistency between flight-production and pre-flight sensor responses under irradiation supports use of the same performance margins for the full focal plane.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same irradiation protocol could be repeated on larger sensor arrays to check whether module-level effects scale to the full focal plane.
  • If the actual space radiation spectrum produces different damage than the 62.4 MeV protons, mission temperature settings might need further revision.
  • These temperature-dependent noise data could help model performance for other DEPFET-based instruments on future X-ray missions.

Load-bearing premise

The 62.4 MeV proton irradiation to a total dose equivalent to 2.6 · 10^9 10-MeV-protons/cm² accurately represents the cumulative total non-ionizing dose the sensors will experience over the NewAthena mission lifetime.

What would settle it

A direct measurement of readout noise and dark current on sensors after the actual NewAthena mission lifetime in orbit that differs substantially from the laboratory proton-irradiation results would show the dose equivalence does not hold.

Figures

Figures reproduced from arXiv: 2606.30169 by Annika Behrens, Astrid Mayr, G\"unter Hauser, Johannes M\"uller-Seidlitz, Leonie Sommer, Luisa Ostler, Peter Lechner, Robert Andritschke, Valentin Emberger, Wolfgang Treberer-Treberspurg.

Figure 1
Figure 1. Figure 1: Left: Picture of a detector module like the ones that were used for the irradiation tests. Right: Setup [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: The distribution of the number of events per frame illustrates the extent of the flux variations. [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Left: Map of the number of protons per pixel. The FWHM of the beam profile is clearly larger than [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Dark current annealing of a detector module after short irradiation (19 s) with a very high dose rate. [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Dark current annealing of the detector module that was irradiated with low dose rate. At least 3 [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Left: Scatterplot of the dose and dark current values of all pixels. The blue dot represents the expected [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Results of the temperature dependent noise characterization. In the left panel the pre-irradiation [PITH_FULL_IMAGE:figures/full_fig_p008_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Measured X-ray spectrum and fit. 4.3 Results The evolution of the threshold voltage is shown in [PITH_FULL_IMAGE:figures/full_fig_p009_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: The reconstructed incident X-ray spectrum. [PITH_FULL_IMAGE:figures/full_fig_p010_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Dose rates during the irradiations. For the first irradiation dose rates were only measured during [PITH_FULL_IMAGE:figures/full_fig_p010_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: DEPFET source voltage measurement that was used to monitor the threshold voltage shift. Prior to [PITH_FULL_IMAGE:figures/full_fig_p011_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Top: The detector stayed at the operating temperature after irradiation. Noise measurements were [PITH_FULL_IMAGE:figures/full_fig_p012_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Results of the temperature dependent noise characterization before irradiation and after annealing [PITH_FULL_IMAGE:figures/full_fig_p012_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Optimal sensor temperature during the mission to minimize the impact of radiation damage on [PITH_FULL_IMAGE:figures/full_fig_p013_14.png] view at source ↗
read the original abstract

The Wide Field Imager (WFI), one of the two instruments on ESA's next large X-ray observatory NewAthena, is designed for imaging spectroscopy in the 0.2-15 keV range, combining a large field of view with high count-rate capability. Its focal plane is equipped with back-illuminated DEPFET (Depleted p-channel field-effect transistor) sensors that offer high radiation tolerance and provide near Fano-limited energy resolution. Achieving this performance requires an exceptionally low readout noise, with about 3 electrons ENC expected at beginning of life. Consequently, the devices are highly sensitive to radiation-induced changes in noise behavior. In this work, we investigate the impact of both total non-ionizing dose (TNID) and total ionizing dose (TID) on the relevant noise components, including their temperature dependence. A detector module containing a 64x64-pixel sensor from a flight-production wafer was irradiated with 62.4 MeV protons at the MedAustron accelerator facility in Wiener Neustadt to a total dose equivalent to 2.6 $\cdot$ 10$^9$ 10-MeV-protons/cm$^2$. The detector was fully biased and operated throughout the irradiation and subsequent measurements, maintaining the nominal operating temperature of 213 K. To study short-term annealing behavior at low temperature, a second, identical module was exposed to a comparable proton dose within a much shorter timescale by exploiting the available high beam flux. TID effects were investigated separately by irradiating another device with 17.4 keV Mo-K_alpha X-rays to a total dose of 15 Gy. We report the resulting changes in readout noise, dark current, and threshold voltage, and compare them with results from an earlier irradiation campaign using pre-flight sensors. Implications for the instrument's required operating temperature and its expected end-of-life performance are discussed.

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

2 major / 0 minor

Summary. The manuscript reports experimental measurements of radiation effects on a flight-production 64x64-pixel DEPFET sensor for the NewAthena WFI. A detector module was irradiated with 62.4 MeV protons to a total dose equivalent to 2.6 · 10^9 10-MeV-protons/cm² while fully biased at 213 K; a second module received a comparable dose on a shorter timescale; and a third device was exposed to 15 Gy TID using 17.4 keV X-rays. Changes in readout noise, dark current, and threshold voltage are quantified and compared to an earlier pre-flight sensor campaign, with discussion of implications for the instrument's required operating temperature and end-of-life performance.

Significance. If the reported changes and their temperature dependence hold, the work supplies directly relevant data on radiation tolerance of flight-grade sensors, supporting refinement of the WFI operating temperature and EOL noise budget for NewAthena. The use of flight-production wafers and in-situ biasing during irradiation adds applicability to actual mission hardware.

major comments (2)
  1. [Abstract / irradiation description paragraph] Abstract, irradiation description paragraph: The central claim that the 62.4 MeV proton irradiation is 'equivalent to 2.6 · 10^9 10-MeV-protons/cm²' and the subsequent EOL performance implications rest on NIEL scaling, yet the manuscript provides no explicit scaling factor, reference to the NewAthena radiation environment model, or uncertainty estimate on the equivalence; this weakens the mapping from lab deltas to flight predictions.
  2. [Results / discussion section (implied by abstract)] Comparison to earlier campaign: The discussion of differences versus the pre-flight sensor results inherits the same unquantified NIEL-scaling assumption; without a dedicated section addressing possible differences in sensor processing, beam spectrum, or annealing conditions, the claimed consistency or divergence cannot be evaluated for robustness.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review. The two major comments identify areas where additional detail on NIEL scaling and comparative analysis will improve clarity and traceability. We address each point below and will incorporate the requested information in the revised manuscript.

read point-by-point responses

  1. Referee: [Abstract / irradiation description paragraph] Abstract, irradiation description paragraph: The central claim that the 62.4 MeV proton irradiation is 'equivalent to 2.6 · 10^9 10-MeV-protons/cm²' and the subsequent EOL performance implications rest on NIEL scaling, yet the manuscript provides no explicit scaling factor, reference to the NewAthena radiation environment model, or uncertainty estimate on the equivalence; this weakens the mapping from lab deltas to flight predictions.

    Authors: We agree that the equivalence statement would benefit from explicit supporting information. In the revised manuscript we will add the NIEL scaling factor applied (derived from the standard 10 MeV proton equivalent fluence for the NewAthena radiation environment), the reference to the mission radiation model used to define the target fluence, and a brief uncertainty estimate based on beam-energy dependence and model assumptions. These additions will be placed in both the abstract and the irradiation-methods paragraph. revision: yes

  2. Referee: [Results / discussion section (implied by abstract)] Comparison to earlier campaign: The discussion of differences versus the pre-flight sensor results inherits the same unquantified NIEL-scaling assumption; without a dedicated section addressing possible differences in sensor processing, beam spectrum, or annealing conditions, the claimed consistency or divergence cannot be evaluated for robustness.

    Authors: We accept that a more structured comparison is required. The revised manuscript will contain a new dedicated subsection that explicitly discusses (i) differences in wafer processing between the pre-flight and flight-production sensors, (ii) the proton beam spectra employed in each campaign, and (iii) the annealing timelines and temperatures. This will allow readers to assess the robustness of the reported consistencies or divergences independently of the NIEL scaling details. revision: yes

Circularity Check

0 steps flagged

No circularity: direct experimental measurements of radiation effects

full rationale

The paper consists of laboratory irradiation of DEPFET sensors with protons and X-rays followed by direct measurements of readout noise, dark current, and threshold voltage shifts. No derivations, first-principles predictions, or fitted parameters are presented that reduce to the inputs by construction. The dose equivalence statement is an experimental design assumption about NIEL scaling, not a self-referential derivation. Comparison to prior campaign data is external benchmarking, not a load-bearing self-citation chain. The work is self-contained against external benchmarks and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper is an experimental measurement study; it relies on standard domain assumptions about radiation dose equivalence and sensor biasing but introduces no free parameters or new entities.

axioms (1)
  • domain assumption 62.4 MeV proton dose can be converted to an equivalent 10-MeV-proton fluence for TNID effects using standard NIEL scaling.
    Invoked to set the irradiation level to the mission-equivalent total non-ionizing dose.

pith-pipeline@v0.9.1-grok · 5920 in / 1260 out tokens · 53360 ms · 2026-06-30T03:50:22.769145+00:00 · methodology

discussion (0)

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Reference graph

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