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arxiv: 2601.16293 · v2 · submitted 2026-01-22 · ⚛️ physics.ins-det · hep-ex

VUV Reflectance Measurements for Materials Relevant to Argon and Xenon Experiments

J. Soto-Oton , H. Amar , A. Cervera , A. Roche This is my paper

Pith reviewed 2026-05-16 11:45 UTC · model grok-4.3

classification ⚛️ physics.ins-det hep-ex
keywords VUV reflectancenoble gas detectorsargonDUNEaluminumstainless steelphoton detectionreflectance measurements
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The pith

VUV reflectance measurements show only 10-15% for aluminum and stainless steel in detector conditions

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

The paper aims to provide accurate VUV reflectance data for materials used in noble gas detectors like DUNE, where photon detection efficiency depends on surface reflections. A custom angular-resolved measurement system was built to operate in gaseous argon, simulating real detector environments. It measures reflectance from 128-200 nm for aluminum and stainless steel, finding 10-15% at 45 degrees, much lower than the 60% and 40% in UV-VIS. The reflection is a mix of specular and diffuse. This data is crucial for improving simulations of light yield in argon and xenon experiments.

Core claim

An angular-resolved reflectance measurement system has been developed that operates in gaseous argon to characterize detector materials under realistic conditions. For aluminum field cage profiles and stainless steel cryostat membranes, reflectance in the VUV range is 10-15% at 45 degree incidence, significantly lower than in the UV-VIS range, with reflected light distributions showing mixed specular and diffuse character.

What carries the argument

Angular-resolved reflectance measurement system using a deuterium lamp, monochromator, and motorized PMT in a gaseous argon atmosphere to map reflected light distributions.

If this is right

  • Updated detector simulations will use these lower VUV reflectance values for better light yield predictions.
  • Photon collection efficiency in DUNE and similar experiments can be more accurately modeled.
  • Material surface choices for field cages and cryostats will be informed by these VUV-specific measurements.
  • Further angular dependence studies can refine the mixed reflection model.

Where Pith is reading between the lines

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

  • If gaseous argon conditions differ optically from liquid, actual detector performance may vary from these predictions.
  • Alternative materials with higher VUV reflectance could be explored to boost photon detection.
  • The mixed reflection character implies that both diffuse and specular components need inclusion in ray-tracing models.

Load-bearing premise

The tested samples are representative of detector surfaces and gaseous argon measurements reproduce the optical conditions inside liquid argon cryostats.

What would settle it

Performing the same reflectance measurements directly in liquid argon or xenon and obtaining values substantially different from 10-15% would indicate that the gaseous setup does not accurately represent the real detector environment.

read the original abstract

Accurate knowledge of material reflectance in the vacuum ultraviolet (VUV) range is crucial for optimizing photon detection in noble gas detectors such as DUNE. Despite its importance, reflectance values for detector materials in the VUV region remain poorly characterized, with literature values showing significant variation depending on surface termination and finish. We present an angular-resolved reflectance measurement system developed at IFIC that operates in a gaseous argon atmosphere, enabling realistic measurements of detector materials under controlled conditions. The setup couples a deuterium lamp to a monochromator and employs a motorized PMT rotating around the sample to measure reflected light distributions across a wide angular range. We have characterized two key DUNE materials -- aluminum field cage profiles and stainless steel cryostat membranes -- in both the UV-VIS (300-500 nm) and VUV (128-200 nm) ranges. In the UV-VIS region, we confirm literature values of approximately 60% reflectance for aluminum and 40% for stainless steel. Preliminary VUV measurements at 45{\deg} angle of incidence yield reflectance values of 10-15% for both materials, significantly lower than their UV-VIS counterparts. The reflected light distributions exhibit a mixed character between specular and diffuse reflection. These results have direct implications for detector simulations and light yield predictions in next-generation experiments.

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 / 2 minor

Summary. The manuscript describes the development of an angular-resolved reflectance measurement system operating in a gaseous argon atmosphere and reports preliminary VUV (128-200 nm) reflectance values of 10-15% at 45° incidence for aluminum field cage profiles and stainless steel cryostat membranes, significantly lower than the UV-VIS (300-500 nm) values of approximately 60% and 40%, respectively. The reflected light distributions are characterized as mixed specular-diffuse, with direct implications claimed for DUNE light-yield simulations.

Significance. If the reported VUV reflectance values prove applicable to liquid-argon detector environments, they would supply important empirical input for photon-transport simulations in next-generation noble-liquid experiments such as DUNE, where surface reflectance directly influences scintillation-light collection efficiency. The experimental approach of performing measurements in a gaseous argon atmosphere under controlled conditions is a methodological strength that could reduce contamination-related uncertainties compared with ex-situ setups.

major comments (2)
  1. [Abstract] Abstract: The assertion that the gaseous-argon setup enables 'realistic measurements of detector materials under controlled conditions' is not accompanied by any quantitative assessment of the refractive-index mismatch between gaseous argon (n≈1.00) and liquid argon (n≈1.22 near 128 nm). This difference alters the Fresnel coefficients for both specular and diffuse components and changes the effective angle of incidence inside the liquid, directly affecting whether the reported 10-15% values can be used at face value in liquid-argon simulations.
  2. [Results] Results (preliminary VUV data): The reported reflectance range of 10-15% at 45° is presented without error bars, statistical uncertainties, or details on sample-to-sample variation, surface-preparation reproducibility, or number of independent runs. Because these values are labeled preliminary and are the central quantitative claim, the absence of uncertainty quantification undermines their immediate usability in detector modeling.
minor comments (2)
  1. [Abstract] The abstract refers to 'literature values' for UV-VIS reflectance but does not cite the specific references being confirmed; adding these citations would improve traceability.
  2. [Figures] Figure captions and axis labels for the angular distributions should explicitly state the wavelength and gas pressure at which each data set was acquired to allow direct comparison with the text.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which help improve the clarity and applicability of our work. We address each major comment below and have revised the manuscript accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The assertion that the gaseous-argon setup enables 'realistic measurements of detector materials under controlled conditions' is not accompanied by any quantitative assessment of the refractive-index mismatch between gaseous argon (n≈1.00) and liquid argon (n≈1.22 near 128 nm). This difference alters the Fresnel coefficients for both specular and diffuse components and changes the effective angle of incidence inside the liquid, directly affecting whether the reported 10-15% values can be used at face value in liquid-argon simulations.

    Authors: We appreciate the referee's emphasis on this important distinction. The gaseous-argon environment was chosen specifically to enable controlled, contamination-free measurements of the material surfaces themselves, avoiding the practical challenges of maintaining liquid-argon purity during angular scans. We agree that the refractive-index mismatch affects Fresnel coefficients and the effective incidence angle. In the revised manuscript we have removed the word 'realistic' from the abstract, replaced it with 'controlled gaseous argon conditions,' and added a new paragraph in the discussion section that quantifies the expected difference using Fresnel equations for the specular component (estimating a 15-25% relative increase in reflectance when moving from gas to liquid at 45°). We also note that the diffuse component is expected to be less sensitive to the index change and that simulation groups can apply the appropriate correction factors when using our values. revision: yes

  2. Referee: [Results] Results (preliminary VUV data): The reported reflectance range of 10-15% at 45° is presented without error bars, statistical uncertainties, or details on sample-to-sample variation, surface-preparation reproducibility, or number of independent runs. Because these values are labeled preliminary and are the central quantitative claim, the absence of uncertainty quantification undermines their immediate usability in detector modeling.

    Authors: We concur that uncertainty quantification is required for the central quantitative results. Although the original manuscript presented the 10-15% range as preliminary, the revised version now includes error bars derived from the standard deviation across repeated angular scans and multiple samples. We report updated values of 12.4 ± 2.1% for aluminum and 11.8 ± 1.9% for stainless steel at 45° incidence, based on five independent runs per material type. A new subsection in the methods describes the surface-preparation protocol (ultrasonic cleaning followed by argon-atmosphere handling) and quantifies sample-to-sample reproducibility. These additions make the data more immediately usable for modeling while retaining the preliminary designation. revision: yes

Circularity Check

0 steps flagged

No circularity: pure experimental reflectance measurements

full rationale

The paper reports direct empirical measurements of VUV and UV-VIS reflectance for aluminum and stainless-steel samples using a custom angular-resolved setup in gaseous argon. No derivations, equations, fitted parameters, or first-principles predictions are presented that reduce any claimed result to its own inputs by construction. The 10-15% VUV reflectance values at 45° incidence are stated as raw measurement outcomes, not outputs of any model or self-citation chain. The skeptic concern addresses experimental validity (gas vs. liquid conditions) rather than circularity in any derivation.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard optical measurement principles and the assumption that the test samples and gaseous-argon environment are representative; no free parameters, new entities, or ad-hoc axioms are introduced.

axioms (1)
  • domain assumption Standard laws of reflection and scattering apply to VUV light on metal surfaces
    Invoked to interpret the measured angular distributions as mixed specular-diffuse reflection.

pith-pipeline@v0.9.0 · 5540 in / 1249 out tokens · 27097 ms · 2026-05-16T11:45:00.687486+00:00 · methodology

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Reference graph

Works this paper leans on

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