{"id":"f6921a5f-7f3d-44ed-bbb2-e5cd77ef2509","arxiv_id":"2506.13826","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":6,"one_line_summary":"ISMRAN's fast neutron response was mapped with a TOF technique, and the measured neutron capture time of about 68 microseconds is consistent with GEANT4 simulation.","lead":"This paper measures how fast neutrons deposit energy in the ISMRAN plastic scintillator detector using time-of-flight with an americium-beryllium source. It also reports a new way to measure the neutron capture time, helping to reject background in reactor antineutrino searches.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The reported 68.29 us capture time is an effective time constant from a single-exponential fit that includes thermalization; the paper never quantifies the GEANT4 agreement, so the assignment to Gd capture is not yet established.","rationale":"The paper's central use is not just the energy-response parametrization; it is the claim that the measured capture-time constant can be used to recognize IBD-like delayed events and to separate correlated fast-neutron background. That use requires tau to be a property of neutron capture on Gd in ISMRAN for the neutron energies relevant to IBD, not merely an effective time constant of the Am-Be measurement. The text of Section 2.2 defines the fit as a single exponential for \"thermalization and capture\" plus constant, so the fitted tau necessarily absorbs the thermalization and diffusion phases. Without a separate thermalization term, a start time offset, or a fit-range scan, the 68.29 us value cannot be assigned to Gd capture. The abstract's claim of agreement with GEANT4 is also unquantified: no simulation curve, fitted value, or comparison metric is given, so the agreement is not independently checkable from the manuscript. The reader's weakest assumption identified the same issue, and this stress-test agrees. A GEANT4 run with capture-isotope tagging is the direct test: it will show whether the selected delayed sample is Gd-dominated and whether the assumed exponential form is correct. If the test passes, the conditional acceptance can move toward acceptance; if it fails, the comparison to IBD delayed capture times should be removed or reframed as an effective background time constant. The paper's TOF-based energy response measurement itself is not in question; the concern is specifically the physical interpretation of tau and the unquantified simulation agreement. Therefore the reader's CONDITIONAL verdict is appropriate, and no change is needed.","tokens_in":4791,"tokens_out":5382,"duration_ms":62237,"concrete_test":"Run a GEANT4 simulation of the exact TOF setup (Am-Be source, first-column prompt tagging, same Esum/Nbars/per-PSB cuts), and for each delayed event record the capturing isotope and the prompt-to-capture time. Fit the simulated Delta-T_cap distribution with the same single-exponential-plus-constant function and also compute the Gd-capture fraction among selected events. If the Gd fraction is >=90% and the fitted tau matches the Gd capture time in the simulation, the interpretation is supported; if the sample contains substantial H captures or the simulated distribution is non-exponential, the measured 68.29 us is an effective parameter and the IBD-discrimination claim must be revised.","verdict_should_be":"UNCHANGED","load_bearing_attack":"In Section 2.2, the Delta-T_cap distribution is fitted with \"an exponential term for the neutron thermalization and capture time in PSBs and a constant term\" (Fig. 6b), and the resulting tau = 68.29 +/- 9.48 us is then interpreted as \"very similar to the characteristic capture time of thermal neutron for IBD delayed events.\" The fit function does not separate thermalization from capture, and no GEANT4 curve, simulated tau, or goodness-of-fit value is shown despite the abstract claiming agreement with simulation. The delayed-event selection (Esum 2.6-10 MeV, Nbars 4-14, per-PSB 0.25-10 MeV) is stated to be benchmarked with GEANT4, but the selected sample is not demonstrated to be dominated by n-Gd captures rather than captures on H or other materials. Consequently, the measured tau is an effective time constant of the full prompt-to-capture process for Am-Be neutrons under the applied cuts; it need not equal the Gd capture time relevant to IBD delayed neutrons, whose source energy and spatial distribution differ. This weakens the summary claim that fast-neutron capture time distributions are indistinguishable from those of nu_e events and the proposed use of tau for IBD/background discrimination.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports TOF-based measurements of the fast-neutron energy response of the ISMRAN plastic-scintillator array using an Am-Be source with a CeBr3 detector triggering on the 4.438 MeV gamma ray. The measured energy deposition versus neutron kinetic energy is fitted with the empirical formula of Eq. (3), and the Delta-T_cap distribution between neutron-tagged prompt events in the first column and delayed candidates in the rest of the array is fitted with an exponential plus a constant term, yielding tau = 68.29 +/- 9.48 microseconds. The authors claim good agreement with GEANT4 simulation and argue that the results will be useful for discriminating correlated fast-neutron background from true IBD events.","tokens_in":5105,"tokens_out":4931,"duration_ms":52672,"significance":"If the response parametrization and the capture-time measurement are robust, they provide useful inputs for ISMRAN background rejection and validate a data-driven method for tagging neutron captures. The paper's strengths include a clear gamma-neutron separation in the TOF spectra (Figs. 2 and 3), a direct measurement of the proton-recoil response curve, and a plausible data-driven approach to the capture-time distribution. However, the absence of a quantitative GEANT4 comparison and the effective rather than pure Gd nature of the fitted tau currently limit the strength of the claims, especially the comparison with IBD delayed-neutron capture times.","major_comments":[{"comment":"The fit function is described only as \"an exponential term for the neutron thermalization and capture time in PSBs and a constant term.\" Consequently, tau = 68.29 +/- 9.48 microseconds is an effective time constant for the combined thermalization-plus-capture process, not the Gd capture time alone. The abstract's characterization as a \"characteristic neutron capture time\" and the summary's statement that the distribution is \"indistinguishable from those of nu_e events\" are therefore not justified by the fit. Please separate the thermalization component (e.g., with a two-exponential fit or a GEANT4 template with known capture time) or explicitly relabel tau as an effective time constant and adjust the physics claims accordingly.","section":"Section 2.2, Fig. 6(b)"},{"comment":"The statement that tau is \"in good agreement with GEANT4 based MC simulation\" is not supported by any quantitative comparison in the paper: no simulated Delta-T_cap spectrum, no simulated tau value, and no goodness-of-fit metric are shown. Please include the GEANT4 prediction overlaid on Fig. 6(b) and report the fitted MC tau with its uncertainty and the pull relative to the data.","section":"Abstract and Section 2.2"},{"comment":"The delayed-event cuts (Esum 2.6-10 MeV, Nbars 4-14, per-PSB 0.25-10 MeV) are stated to be benchmarked with GEANT4, but the composition of the selected sample is not demonstrated. If a substantial fraction of captures occurs on hydrogen or other nuclides rather than on Gd, the fitted tau is a weighted average over capture channels and the comparison with the IBD Gd capture time is misleading. Please report the simulated fractions of capture channels in the accepted sample and, if needed, adjust the interpretation.","section":"Section 2.2, delayed-event selection"},{"comment":"No systematic uncertainties are reported; the quoted errors on the Eq. (3) parameters and on tau appear to be statistical only. The results depend on the source-detector distance L, the T0 calibration from the gamma peak, the CeBr3 energy calibration, and the PSB energy scale. The propagation of these systematic effects into the Edep-versus-En parametrization and into tau should be quantified before the results are used for background discrimination.","section":"Throughout the manuscript"}],"minor_comments":[{"comment":"Please write out the explicit fit function used for Fig. 6(b), including the constant term and the fit range; the current description is insufficient to reproduce the fit.","section":"Section 2.2"},{"comment":"The fitted parameter values are typeset in a garbled way (\"A : 0.41 0.03 +/- ...\" and similar); please correct the formatting so that each parameter and its uncertainty are unambiguous.","section":"Fig. 5"},{"comment":"The panel annotations \"pos PS\" and \"Z0.5\" appear incomplete; please clarify that these denote the PSB hit position and the z-window used in the event selection.","section":"Fig. 4(a)"},{"comment":"The phrase \"scaled with the neutron events above Delta-T > 300 microseconds\" is unclear; please rephrase to describe how the gamma-tagged distribution was normalized for comparison with the neutron-tagged distribution.","section":"Section 2.2, Fig. 6(a)"},{"comment":"The reference list contains only two self-references; adding standard references for the Am-Be neutron spectrum, the GEANT4 simulation toolkit, and neutron capture on Gd would help readers place the work in context.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of physics.ins-det. The central issues are the over-interpretation of the effective capture time as a pure Gd capture time and the missing quantitative GEANT4 comparison; both are addressable in revision. I do not see a circularity problem: the response parametrization is fitted to an independent TOF dataset even though the functional form comes from ref. [2]. However, the heavy reliance on two self-references is worth monitoring during the revision."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Plain take: this is a useful detector-characterization measurement, not a breakthrough. The new bits are the TOF-based neutron response on the full 90-bar ISMRAN array and the capture-time distribution measured by tagging neutrons in the first column and looking for delayed events in the rest of the array. That combination is new relative to the group's earlier prototype and D-D/D-T work, and the technique is sensible. The TOF gamma-neutron separation in Fig. 2/3 looks clean, and the response parametrization in Fig. 5 is plausible, with reasonable fit errors.\n\nThe soft spot is the capture-time interpretation. Section 2.2 fits ΔT_cap with a single exponential that explicitly includes both thermalization and capture, then calls the resulting tau = 68.29 ± 9.48 us \"the characteristic neutron capture time\" and claims it is \"very similar\" to IBD delayed neutron capture. But a single exponential that lumps thermalization with capture is an effective time constant for Am-Be neutrons under your cuts, not necessarily the Gd capture time. The problem is compounded by the abstract: \"good agreement with GEANT4\" is never shown. No simulated curve, no simulated tau value, no goodness-of-fit. That makes the agreement claim unverifiable. The summary's statement that fast-neutron capture distributions are indistinguishable from νe events goes beyond what the data support, because the selected delayed sample may include captures on H or other materials, and the source energy/spatial distribution differs from IBD neutrons. These are fixable in revision: show the GEANT4 prediction, separate thermalization from capture in the fit if possible, or at minimum label tau as an effective time constant and discuss what it means for background rejection.\n\nSystematic uncertainties are absent, which is a real gap for a measurement paper. The response parametrization would benefit from at least an estimate of the TOF binning smearing and source-position uncertainties. None of this is fatal; the central measurement is credible and the TOF tagging is a legitimate way to study correlated backgrounds.\n\nWho is this for? ISMRAN collaborators and anyone working on segmented plastic scintillator detectors with Gd-coated bars. It deserves a serious referee, but I would want the authors to address the capture-time interpretation and provide the missing GEANT4 comparison before it is accepted. The paper is honest in its methods and clearly builds on the group's own prior work, so I have no concern about the citation pattern.","headline":"A credible TOF-based neutron response measurement for ISMRAN, with a capture-time result that is real but currently overinterpreted as the Gd capture time.","tokens_in":5634,"tokens_out":1530,"would_cite":false,"duration_ms":19471,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["29.40.Mc","29.30.Hs"],"model":"deepseek-v4-flash","headline":"This paper establishes a time-of-flight method for measuring fast-neutron energy response and capture time in the ISMRAN detector array, reporting a capture time of 68.29 ± 9.48 μs that matches the delayed signature of inverse beta decay.","keywords":["time-of-flight neutron spectroscopy","plastic scintillator bars","gadolinium neutron capture","reactor antineutrino detection","inverse beta decay background","Am-Be neutron source","neutron capture time"],"falsifier":"Measure the $\\Delta T_{\\rm cap}$ distribution separately for low-energy and high-energy tagged neutrons; if the 68 μs component is genuine capture on gadolinium it should be independent of the neutron's initial energy, whereas if thermalization contributes significantly the fitted time constant will shift between energy bins. A second check is to replace the gadolinium-coated wrappers with plain reflective foil and observe whether the measured $\\tau$ disappears or changes; if it does not, the fitted exponential is not dominated by gadolinium capture.","tokens_in":4634,"feed_emoji":"⚛️","tokens_out":8124,"duration_ms":80536,"temperature":0.7,"pith_summary":"The paper reports a measurement of how fast neutrons deposit energy in the ISMRAN detector, a 9×10 array of plastic scintillator bars wrapped in gadolinium-coated foil, using a time-of-flight technique with an americium-beryllium source. By tagging the 4.438 MeV gamma ray that accompanies each source neutron, the authors convert neutron flight times into kinetic energies and map them to proton-recoil light yields. They then use the tagged neutrons as prompt events and search the rest of the array for delayed neutron-capture candidates, obtaining a characteristic capture time of 68.29 ± 9.48 μs. That time matches the Monte Carlo prediction and is close to the delayed-neutron capture time expected in inverse beta decay events, which matters because it means the capture-time signature alone cannot separate fast-neutron background from genuine reactor antineutrino events; additional spatial and energy-shape cuts are needed.","feed_headline":"Fast-neutron capture time measured at 68 microseconds in ISMRAN","feed_subtitle":"Time-of-flight tagging matches the delayed-neutron signature used to spot reactor antineutrinos.","key_machinery":"The central mechanism is neutron tagging by time of flight. A $^{241}$Am-$^{9}$Be source emits a 4.438 MeV gamma ray in about 60% of disintegrations, and detecting that gamma in a CeBr$_3$ scintillator provides the start time; the stop time comes from the first column of the ISMRAN array, so the flight time to each bar separates gammas from neutrons. From the flight distance $L$ and time $t$, the neutron kinetic energy is obtained from $E_n = \\frac{1}{2}m(L/t)^2$, written as $E_n = \\alpha^2 L^2/t^2$ with $\\alpha = 72.3\\ \\sqrt{\\text{eV}}\\,\\mu\\text{s/m}$. The proton-recoil light yield in the bars is then fitted to an empirical formula $E_{\\rm dep} = A E_n - B(1 - e^{-C E_n^D})$. For the capture-time measurement, the tagged neutron in the first column acts as the prompt event and delayed candidates in the remaining bars are required to satisfy energy and multiplicity cuts; the $\\Delta T_{\\rm cap}$ distribution is fitted by a single exponential (neutron thermalization and capture) plus a constant (accidental background), yielding the characteristic capture time.","core_discovery":"The central claim is that the ISMRAN array's response to fast neutrons can be measured end-to-end with a data-driven time-of-flight method, and that the measured neutron capture time distribution is characterized by $\\tau = 68.29 \\pm 9.48\\ \\mu$s. The experiment uses a $^{241}$Am-$^{9}$Be source, with a cerium bromide detector registering the 4.438 MeV de-excitation gamma ray as the start signal and the first column of plastic scintillator bars as the stop signal. With the gamma and neutron bands cleanly separated in time of flight, the neutron kinetic energy is computed from flight distance and time, and the resulting proton-recoil energy deposition is parametrized by an empirical formula. The same tagged neutrons serve as a prompt population; delayed events recorded in the rest of the array within 1000 μs, selected by energy-sum, per-bar energy, and number-of-bars cuts, produce a capture-time distribution whose exponential-plus-constant fit gives the reported $\\tau$. On these measurements the paper builds the claim that fast-neutron capture is indistinguishable in time from inverse $\\beta$ decay delayed captures, and therefore background rejection must rely on spatial and energy-distribution variables rather than timing alone.","pith_inferences":["Editorial inference: the same prompt-delayed pairing could be applied with the tagged neutron's kinetic energy as an additional variable, allowing a two-dimensional (energy, capture-time) model that separates thermalization from pure capture and could tighten background rejection.","Editorial inference: if applied to a detector with variable gadolinium loading or without gadolinium, the method could turn the measured $\\tau$ into an in-situ diagnostic of capture-material fraction.","Editorial inference: the reported single-exponential fit could be tested against a two-component hydrogen-plus-gadolinium model; the fitted amplitudes would reveal whether the current cuts are actually gadolinium-dominated before the array is used for reactor antineutrino monitoring.","Editorial inference: the approach could be transferred to other segmented plastic-scintillator antineutrino detectors, since it uses only a compact Am-Be source and a gamma trigger rather than a pulsed neutron beam."],"forward_implications":["The measured $\\tau$ of 68.29 ± 9.48 μs can be used to set the delayed-coincidence window for inverse beta decay candidate selection in ISMRAN, since true delayed events should follow the same capture-time distribution.","The proton-recoil light-yield parametrization from Eq. (3) gives input for simulating fast-neutron backgrounds, improving the modeling of correlated background in reactor ON and OFF running.","Because fast-neutron captures and inverse beta decay delayed captures have indistinguishable time constants, the array must rely on its segmented geometry, energy-ratio variables, and machine-learning classification to separate the two populations.","The time-of-flight tagging method itself is a reusable, data-driven way to measure neutron capture times in a segmented scintillator array without a dedicated neutron beam."],"supporting_citations":[{"why":"Supplies the prototype ISMRAN bar design and the detector-response measurements on which the full-array simulation and event-selection cuts are benchmarked.","marker":"[1]"},{"why":"Gives the empirical neutron light-yield parametrization and the earlier fast-neutron characterization method from D-D and D-T reactions that this paper adapts to the Am-Be time-of-flight measurement.","marker":"[2]"}],"fun_headline_variants":["ISMRAN times fast neutrons: capture time 68 μs","Neutron capture time measured at 68 μs via TOF","TOF technique measures ISMRAN neutron capture at 68 μs","Fast-neutron capture time 68 μs from ISMRAN TOF"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that the delayed-event sample selected by the energy-sum, per-bar energy, and bar-multiplicity cuts is dominated by neutron capture on gadolinium and that its capture-time distribution is a single exponential, so the fitted 68.29 μs is the true gadolinium capture time rather than an effective average over several capture processes.","fun_headline_variants_meta":{"raw":{"variants":["ISMRAN times fast neutrons: capture time 68 μs","Neutron capture time measured at 68 μs via TOF","TOF technique measures ISMRAN neutron capture at 68 μs","Fast-neutron capture time 68 μs from ISMRAN TOF"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000637,"raw_usage":{"total_tokens":3002,"prompt_tokens":1080,"completion_tokens":1922,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":696,"completion_tokens_details":{"reasoning_tokens":1842}},"tokens_in":696,"tokens_out":1922,"duration_ms":15162,"temperature":1.0,"reasoning_tokens":1842,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T00:36:24.336349+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the $\\Delta T_{\\rm cap}$ distribution separately for low-energy and high-energy tagged neutrons; if the 68 μs component is genuine capture on gadolinium it should be independent of the neutron's initial energy, whereas if thermalization contributes significantly the fitted time constant will shift between energy bins. A second check is to replace the gadolinium-coated wrappers with plain reflective foil and observe whether the measured $\\tau$ disappears or changes; if it does not, the fitted exponential is not dominated by gadolinium capture.","supporting_citations":[{"cited_title":"Scherzinger","cited_arxiv_id":null,"evidence_quote":"Supplies the prototype ISMRAN bar design and the detector-response measurements on which the full-array simulation and event-selection cuts are benchmarked."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the empirical neutron light-yield parametrization and the earlier fast-neutron characterization method from D-D and D-T reactions that this paper adapts to the Am-Be time-of-flight measurement."}],"review_version":1}