{"id":"51130c80-1943-4c40-910b-4eb1787d799f","arxiv_id":"2505.08513","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Self-absorption in organic glass scintillators reduces photoelectron yield and pulse shape discrimination figure of merit with increasing detector height, while the normalized figure of merit stays constant.","lead":"This paper measures how organic glass scintillators lose performance as they get larger, and shows the loss is tied to the material absorbing its own light. The results give detector designers practical guidance on size limits and optimal settings for neutron-gamma discrimination.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The intrinsic normalized-FOM claim rests on an unverified assumption that the pulse shape is independent of scintillator height; only the 25 mm sample's pulse shape was measured (Sec. 3.2).","rationale":"The reader's weakest assumption identifies exactly the point on which the central claim depends: the size independence of the pulse shape. I agree that this is the most load-bearing assumption. If it fails, the 'intrinsic normalized FOM' conclusion in Sec. 3.1 is not valid, and predictions of FOM for other detector sizes from a single measurement would be unreliable. The paper's own data support the assumption only indirectly. The FOM/sqrt(Nphe) values in Table 1 are consistent with a constant within quoted uncertainties, but they are also consistent with a slight increase, and the optimal-gate evidence is coarse. The absence of direct pulse-shape measurements for taller samples is an explicit gap, acknowledged by the wording in Sec. 4. I do not see a more serious internal inconsistency: the measurements are carefully described, the statistical uncertainties are reported, and the empirical scaling of FOM with Nphe is plausible. The paper should be accepted with the condition that the pulse-shape invariance is tested on at least one additional sample height, e.g., the 125 mm sample. This does not change the reader's CONDITIONAL verdict, hence UNCHANGED.","tokens_in":9366,"tokens_out":11238,"duration_ms":105758,"concrete_test":"Measure neutron and gamma pulse shapes of the 125 mm OGS sample using the same Bollinger-Thomas setup (Fig. 5) over the same 350–1250 keVee range, fit Eq. (5) with the same genetic-algorithm procedure, and compare the three decay times and intensities with Table 3 values for the 25 mm sample. If all parameters agree within their quoted 2-sigma uncertainties, the intrinsic normalized-FOM claim is corroborated for the size range studied; if the slow-component decay time or intensity changes by more than the quoted uncertainties, the assumption fails and the constant normalized FOM cannot be interpreted as an intrinsic property.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central predictive claim is that FOM/sqrt(Nphe) is an intrinsic scintillator property, so the observed FOM decline with height can be attributed entirely to the loss of photoelectrons. This requires the pulse shape (decay constants and component intensities in Eq. 5) to be identical for all five heights. However, direct Bollinger-Thomas pulse-shape data are presented only for the 25 mm OGS (Sec. 3.2); no pulse-shape measurement is reported for the 55, 78, 102, or 125 mm samples. The supporting evidence — constant normalized FOM in Table 1 and size-independent optimal gates in Table 2 — is indirect. Gate optimality is insensitive to subtle PSD-relevant changes because gates are scanned in coarse steps (4 ns short, 50 ns long), and the long gates at 100 keVee vary from 270 to 300 ns with height, a spread comparable to the 50 ns scan step. Self-absorption is wavelength-dependent; if re-emission or differential attenuation of fast/slow components changes the effective pulse shape with size, the neutron-gamma centroid separation in Eq. (2) changes, and the constant normalized FOM becomes coincidental rather than intrinsic. The conclusion's statement that 'we found no evidence that the pulse shape itself undergoes any change' (Sec. 4) is an absence-of-evidence assertion, not a direct measurement. Thus the use of a single-sample measurement to predict FOM for arbitrary detector sizes is not yet established.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a systematic study of five cylindrical organic glass scintillator samples of identical 25.4 mm diameter and heights from 25 mm to 125 mm, plus a trans-stilbene reference. Using the Bertolaccini method it measures photoelectron yield, and using a charge-comparison pulse-shape-discrimination (PSD) analysis with scanned gates it measures the neutron-gamma Figure of Merit (FOM) over energies from 100 to 1000 keVee. It finds that both photoelectron yield and FOM decrease with increasing scintillator height, while the FOM normalized by the square root of the number of photoelectrons remains approximately constant. The decrease is attributed to light self-absorption. The paper also reports Bollinger-Thomas pulse-shape measurements for the 25 mm OGS and for trans-stilbene, fitted with a genetic algorithm to extract three exponential decay components, and compares OGS and stilbene decay times and intensities.","tokens_in":9691,"tokens_out":4381,"duration_ms":45360,"significance":"If the central claim holds, the constant normalized FOM would be a practically useful result: it implies that, at a given deposited energy, the neutron-gamma discrimination performance of an OGS detector can be predicted from a single photoelectron-yield measurement, and that the degradation of PSD with size is driven purely by photoelectron statistics rather than by a change in the intrinsic pulse shape. The dataset is valuable: five physical heights, repeated measurements with re-coupling, propagated uncertainties, and a consistent analysis pipeline. The comparison with EJ-276 plastic and trans-stilbene adds context. The paper's direct measurements of yield and FOM are sound; the main caveat is that the 'intrinsic property' conclusion rests on an assumption about pulse-shape invariance that is supported only indirectly.","major_comments":[{"comment":"The FOM values in Table 1 are obtained with fixed gates (short = 66 ns, long = 350 ns), which are not exactly the optimal gates for all samples according to Table 2 (for example, at 300 keVee the optimal long gate for the 55, 78, and 102 mm samples is 330 or 350 ns). The fixed-gate choice affects the absolute FOM values but not the overall trend. This is a minor methodological point, but it means that the normalized FOM values in Table 1 are not all evaluated at the maximum FOM for each sample. The authors should either state that the fixed gates are representative and that the maximum-FOM comparison in Table 2 gives the same qualitative result, or justify the use of fixed gates for the intrinsic-property claim.","section":"Section 2.2 and Table 1"}],"minor_comments":[{"comment":"In the paragraph discussing the linear relation between yield and size, the text mentions 'the 136Cs source', which appears to be a typo for '137Cs'.","section":"Section 3.1"},{"comment":"The sentence 'In case of the scintillators used in our research peak on the right side represents pulses induced by fast neutrons...' is missing a comma after 'research' and should be rephrased for clarity.","section":"Section 3.1"},{"comment":"The caption states that 'R2 and reduced χ2 values were calculated to confirm that the results are reliable' but the actual values are not reported anywhere in the text or tables. Please include them or remove the sentence.","section":"Figure 13 caption"},{"comment":"The footnote says that the uncertainty of the gates can be estimated as the step size (4 ns for short, 50 ns for long), but the text in Section 3.1 says the averaged gates were rounded to 2 ns and 10 ns, respectively. Clarify which uncertainty is meant to be quoted.","section":"Table 2"},{"comment":"The phrase 'the uncertainties of decay times were estimated as 2σ of Gaussian fit' in the note to Table 3 is slightly ambiguous: it should specify that the Gaussian is fit to the distribution of parameter values obtained from the repeated genetic-algorithm runs, and that the reported value is the mean of that Gaussian.","section":"Section 3.2"},{"comment":"The paper uses 'we' extensively in the results sections; this is acceptable in this venue, but the manuscript would benefit from a brief list of the analysis software versions and a statement on data availability, since the custom Python software is described but not deposited.","section":"Throughout"},{"comment":"Reference [6] is an arXiv preprint; if a published version exists by the time of submission, it should be cited. Also, reference [4] is a web page; please add a retrieval date.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper presents a clean experimental dataset and a sensible analysis, and the basic result (FOM and yield decrease with height) is solid. My main reservation is that the central interpretive claim - that normalized FOM is an intrinsic scintillator property and that self-absorption is the demonstrated cause - goes beyond what the data directly show. The authors should either provide direct absorption spectra and pulse-shape data for at least one taller sample, or carefully re-word the conclusions to reflect the indirect nature of the evidence. This is fixable within the scope of the manuscript, so I recommend major revision rather than rejection. The manuscript is within the scope of the journal and will be of interest to the detector community, especially given the growing use of organic glass scintillators."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a solid, incremental detector-physics paper. The new and useful result is that the FOM of organic glass scintillators falls with sample height at fixed diameter, and FOM/sqrt(Nphe) stays roughly constant across five sizes. That makes normalized FOM a practical predictor for detector size effects, and the data are good enough to take it seriously.\n\nWhat stands out: the five uniform OGS samples are a real improvement over the stacked-sample study in ref [5]; no interface losses. Photoelectron yields, FOM values, and uncertainties come from repeated measurements, and the trends are internally consistent. The genetic-algorithm fits of the multi-exponential pulse shapes are a reasonable way to extract decay times, and the comparison with trans-stilbene gives the reader context. The gate-choice guidance at the end is also practically useful.\n\nThe soft spots, in proportion: the central 'intrinsic normalized FOM' claim rests on the assumption that the pulse shape itself does not change with height, because FOM/sqrt(Nphe) is only a good intrinsic metric if the centroid separation and widths scale only with photoelectron statistics. Direct Bollinger-Thomas pulse-shape data are presented only for the 25 mm sample; the invariance across 55-125 mm is inferred from the constant normalized FOM and from optimal gates being roughly stable. That is decent circumstantial evidence, and the coarse gate scans (4 ns short, 50 ns long) are not very sensitive to subtle shape changes. It is not, however, a direct measurement. I would not call the claim wrong - I think it is probably right - but the wording 'intrinsic property of the scintillator' is a step beyond what was directly measured. A pulse-shape run on one taller sample, or softened wording, would fix it.\n\nSecond, the attribution to self-absorption is inferred from the yield decrease with height; no absorption spectrum or wavelength-resolved measurement is shown. That is consistent and likely true, but it is an interpretation. Also, no raw data or code are released, so independent checks of the fits are limited, though the fitted pulse shape parameters are reported with uncertainties.\n\nWho this is for: applied radiation detection - people building neutron/gamma detectors with OGS, and groups benchmarking PSD materials. It does not reshape the field, but it gives a scaling rule that was missing. I would send it to peer review. The central result is reproducible from the tables, and the one missing measurement is clear.","headline":"Solid incremental OGS characterization: normalized FOM is a useful size-scaling metric, but the 'intrinsic' claim needs direct pulse-shape measurements beyond the 25 mm sample.","tokens_in":10175,"tokens_out":2462,"would_cite":true,"duration_ms":25158,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["29.40.Mc"],"model":"deepseek-v4-flash","headline":"Organic glass scintillators lose neutron-gamma discrimination as they grow because self-absorption cuts the number of detected photoelectrons; their normalized discrimination quality remains constant.","keywords":["organic glass scintillator","self-absorption","pulse shape discrimination","neutron-gamma discrimination","figure of merit","photoelectron yield","charge comparison method","scintillator size effects"],"falsifier":"Measure the three-exponential decay times and intensities of neutron- and gamma-induced pulses on a 125 mm cylinder with the same delayed single-photon setup; if the fast, medium, and slow component intensities differ from the 25 mm sample beyond uncertainties, then FOM loss is not purely a photoelectron-statistics effect and normalized FOM is not fully intrinsic.","tokens_in":9217,"feed_emoji":"☢️","tokens_out":9128,"duration_ms":81850,"temperature":0.7,"pith_summary":"Organic glass scintillators are promising solid alternatives to flammable liquid scintillators for detecting neutrons and gamma rays, but their performance depends on detector size. This paper claims that the loss of neutron-gamma discrimination in taller scintillators is caused by self-absorption of the scintillation light, which reduces the number of photoelectrons reaching the photomultiplier, and not by any change in the pulse shape itself. The evidence comes from five cylinders of the same diameter with heights from 25 mm to 125 mm: as height grows, both photoelectron yield and figure of merit fall, while the figure of merit normalized to the square root of the photoelectron number stays constant. If the claim is right, detector performance at a given energy can be predicted from a single measurement, and self-absorption sets a concrete upper limit on useful detector size.","feed_headline":"Self-absorption, not pulse shape, limits organic glass detector size","feed_subtitle":"Taller cylinders lose neutron-gamma separation because fewer photons arrive; normalized figure of merit holds steady.","key_machinery":"The load-bearing quantity is the normalized figure of merit, $\\mathrm{FOM}/\\sqrt{N_{\\mathrm{phe}}}$, which stays constant across all five heights and is proposed as an intrinsic scintillator property. It is built from charge-comparison pulse shape discrimination, where each pulse gets a parameter $\\mathrm{PSD} = (Q_{\\mathrm{long}} - Q_{\\mathrm{short}})/Q_{\\mathrm{long}}$, and the figure of merit is the separation of the neutron and gamma centroids divided by the sum of their full widths at half maximum. The decisive experimental design is a set of five cylinders with identical 25.4 mm diameter and heights from 25 mm to 125 mm, so the self-absorption path length grows with height without any stacked-sample interface losses. The pulse shape itself is examined with a delayed single-photon coincidence setup and fitted with a three-exponential decay using a genetic algorithm, showing no significant change in decay times across energy and supporting the interpretation that FOM loss is statistical rather than a shape change.","core_discovery":"The central claim is that light self-absorption inside an organic glass scintillator degrades neutron-gamma pulse shape discrimination purely by cutting photoelectron statistics, not by altering the scintillation pulse shape. At 300 keVee the figure of merit drops from $2.37 \\pm 0.07$ for the 25 mm sample to $1.70 \\pm 0.05$ for the 125 mm sample, while the photoelectron yield falls from $4310 \\pm 420$ to $1760 \\pm 330$ per MeV. The ratio $\\mathrm{FOM}/\\sqrt{N_{\\mathrm{phe}}}$ stays within $0.066$ to $0.074$, that is, constant within uncertainties. The paper therefore concludes that normalized FOM at a given energy is an intrinsic property of the scintillator, that optimal charge-comparison gates are independent of detector size, and that self-absorption imposes a limit on the maximum useful detector size. The samples retain higher discrimination quality than the EJ-276 plastic comparison and remain broadly comparable to liquid EJ-309.","pith_inferences":["A direct measurement that would sharpen the claim is a single-photon pulse-shape run on a 125 mm cylinder; the paper's height-independence of pulse shape is inferred, not measured.","If normalized FOM is truly size-invariant, the same one-sample-plus-scaling characterization could be applied to other self-absorbing scintillators, reducing the number of prototypes needed to predict field performance.","The linear rather than exponential falloff of yield with height hints that reflective boundaries and source geometry, not simple Beer-Lambert attenuation, set the effective path length; a light-transport model could separate those contributions.","Because optimal gates vary with energy in every sample tested, a fixed-gate instrument may silently lose low-energy separation; an energy-dependent or two-gate readout scheme is a testable engineering response."],"forward_implications":["Practical detector design must treat self-absorption as a size ceiling: FOM at 300 keVee falls steadily from $2.37$ at 25 mm to $1.70$ at 125 mm, and the trend continues.","A single measurement of normalized FOM at a given energy, combined with the photoelectron-yield scaling curve, predicts the FOM of untested detector heights.","Optimal charge-comparison gates are size-independent but energy-dependent; for wide energy ranges, choosing gates tuned to the lowest energy avoids a catastrophic loss of separation at low energy with only a small penalty at high energy.","With FOM above 1 even for the tallest tested sample, organic glass scintillators remain usable at moderate sizes and, thanks to short pulses, can sustain higher count rates than trans-stilbene crystals."],"supporting_citations":[{"why":"Earlier measurement on stacked 2-inch organic glass scintillator samples that first connected size-dependent FOM loss to self-absorption; this paper extends that result to seamless cylinders.","marker":"[5]"},{"why":"Provides EJ-276 plastic scintillator data used as the comparison showing that organic glass scintillators exhibit stronger self-absorption.","marker":"[12]"},{"why":"Supplies the calibration method for absolute photoelectron yield per keV, which anchors the yield measurements used in the normalized FOM.","marker":"[9]"},{"why":"Delayed single-photon coincidence method used to record pulse shapes for the decay-component analysis.","marker":"[11]"},{"why":"Earlier work establishing the offline digital pulse analysis and gate optimization procedure used throughout this study.","marker":"[6]"},{"why":"Establishes the 80%-of-maximum Compton edge convention used for energy calibration in low-Z scintillators.","marker":"[8]"}],"fun_headline_variants":["Self-absorption, not pulse shape, sets organic glass size limit","Photon loss, not pulse distortion, degrades big scintillators","Normalized FOM holds: self-absorption only steals photons","Organic glass size limited by self-absorption, not pulse shape"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The argument assumes the scintillation pulse shape does not change as the detector grows, so all loss of discrimination is blamed on fewer detected photons; that assumption is inferred from the constant normalized figure of merit, not measured on the taller samples.","fun_headline_variants_meta":{"raw":{"variants":["Self-absorption, not pulse shape, sets organic glass size limit","Photon loss, not pulse distortion, degrades big scintillators","Normalized FOM holds: self-absorption only steals photons","Organic glass size limited by self-absorption, not pulse shape"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000228,"raw_usage":{"total_tokens":1447,"prompt_tokens":889,"completion_tokens":558,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":505,"completion_tokens_details":{"reasoning_tokens":484}},"tokens_in":505,"tokens_out":558,"duration_ms":5624,"temperature":1.0,"reasoning_tokens":484,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T21:52:25.099352+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the three-exponential decay times and intensities of neutron- and gamma-induced pulses on a 125 mm cylinder with the same delayed single-photon setup; if the fast, medium, and slow component intensities differ from the 25 mm sample beyond uncertainties, then FOM loss is not purely a photoelectron-statistics effect and normalized FOM is not fully intrinsic.","supporting_citations":[{"cited_title":"Grodzicka-Kobylka, T","cited_arxiv_id":null,"evidence_quote":"Earlier measurement on stacked 2-inch organic glass scintillator samples that first connected size-dependent FOM loss to self-absorption; this paper extends that result to seamless cylinders."},{"cited_title":"Grodzicka-Kobylka, T","cited_arxiv_id":null,"evidence_quote":"Provides EJ-276 plastic scintillator data used as the comparison showing that organic glass scintillators exhibit stronger self-absorption."},{"cited_title":"Bertolaccini, S","cited_arxiv_id":null,"evidence_quote":"Supplies the calibration method for absolute photoelectron yield per keV, which anchors the yield measurements used in the normalized FOM."},{"cited_title":"Bollinger and G.E","cited_arxiv_id":null,"evidence_quote":"Delayed single-photon coincidence method used to record pulse shapes for the decay-component analysis."},{"cited_title":"Advantages of off-line analysis of digitally recorded pulses in case of neutron-gamma discrimination in scintillators","cited_arxiv_id":"2504.11963","evidence_quote":"Earlier work establishing the offline digital pulse analysis and gate optimization procedure used throughout this study."},{"cited_title":"Swiderski, M","cited_arxiv_id":null,"evidence_quote":"Establishes the 80%-of-maximum Compton edge convention used for energy calibration in low-Z scintillators."}],"review_version":1}