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arxiv: 2512.02277 · v3 · pith:MKL7KH4Dnew · submitted 2025-12-01 · ⚛️ nucl-ex

Measuring ^(19,20)O(p,n)^(19,20)F reactions using an active target detector

Rohit Kumar , H. Desilets , R.T. deSouza This is my paper

Pith reviewed 2026-05-21 17:34 UTC · model grok-4.3

classification ⚛️ nucl-ex
keywords active target detectorinverse kinematics(p,n) reactionproton fusionoxygen isotopesbackground rejectioncross section extractionnuclear reactions
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The pith

Background rejection in an active target isolates the (p,n) channel to access proton fusion cross sections on 19O and 20O.

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

The paper measures proton capture on oxygen-19 and oxygen-20 in inverse kinematics by directing the beams into an active target filled with methane gas. Unreacted beam particles, inelastically scattered events, and reactions on the carbon component of the target are rejected to isolate the (p,n) events. At the relevant beam energies the direct (p,n) contribution is small, so the extracted cross section effectively reports the proton fusion rate. The authors present a detailed analysis procedure that converts the accepted events into a fusion cross section value.

Core claim

Proton capture on 19,20O nuclei is measured in inverse kinematics with an active target detector using CH4 as the target gas. Rejection of unreacted and inelastically scattered beam, along with transfer and fusion on the 12C allows extraction of the (p,n) cross section. As the cross-section for direct (p,n) processes at these energies is small, the measurement provides access to the proton fusion cross-section.

What carries the argument

Background rejection of unreacted beam, inelastic scattering, transfer reactions, and fusion on 12C within the active target volume.

If this is right

  • The (p,n) cross section is obtained directly from the events that survive the rejection criteria.
  • This (p,n) value serves as a proxy for the proton fusion cross section because the direct (p,n) contribution is negligible at the studied energies.
  • The described analysis procedure converts raw detector signals into a quantitative fusion cross section.

Where Pith is reading between the lines

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

  • The same rejection strategy could be tested on beams of other light nuclei to see whether fusion cross sections remain accessible when direct (p,n) channels are suppressed.
  • Measured fusion values could be compared with theoretical models of proton-induced reactions on neutron-rich oxygen isotopes.
  • Varying the hydrogen-to-carbon ratio in the target gas would provide a direct check on the cleanliness of the carbon-background subtraction.

Load-bearing premise

The background rejection techniques cleanly separate the (p,n) channel from all other processes without significant contamination or efficiency losses that would bias the extracted fusion cross section.

What would settle it

Detection of a substantial fraction of events from carbon fusion or inelastic scattering remaining in the final (p,n) sample after all rejection cuts would show that the separation is incomplete.

Figures

Figures reproduced from arXiv: 2512.02277 by H. Desilets, Rohit Kumar, R.T. deSouza.

Figure 1
Figure 1. Figure 1: The incident O ion can undergo elastic or inelastic scat [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 1
Figure 1. Figure 1: Schematic illustration of the different reaction channels. CN E∗ (MeV) n(%) α(%) αn(%) p(%) 20F 12.1 98.2 1.8 0.0 0.0 20F 12.6 92.0 2.3 5.7 0.0 21F 12.2 >99.9 0.0 0.0 0.0 21F 13.3 99.8 0.1 0.0 0.1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: Flowchart depicting the analysis logic utilized. [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Identification of the incident beam based upon the energy deposit of [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: Deviation of each event trace from the average O and F reference [PITH_FULL_IMAGE:figures/full_fig_p004_6.png] view at source ↗
Figure 5
Figure 5. Figure 5: Putative proton fusion trace (solid, magenta) is compared to a few [PITH_FULL_IMAGE:figures/full_fig_p004_5.png] view at source ↗
Figure 7
Figure 7. Figure 7: Distribution of <E> a f ter. Two peaks are visible: the left peak corre￾sponds to scattered beam events and the right peak corresponds to proton fusion events. The beam scattered events are rejects by the vertical (red) line. 3.5. Stage 5: Select events based on <E>a f ter To further select proton fusion, specifically isolating it from proton two-body scattering (elastic or inelastic), the quantity ⟨E⟩a f … view at source ↗
Figure 8
Figure 8. Figure 8: Correlation between the O-deviation and the F-deviation for events [PITH_FULL_IMAGE:figures/full_fig_p005_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Dependence of the cross section for 19O(p,n) and 20O(p,n) on Ecm. The Bass barrier, VB [6] for each system is indicated by the arrows: VB = 1.47 MeV for 19O and VB = 1.46 MeV for 20O. intrinsically provide an angle-integrated measurement of the cross-section. The uncertainty in the measured cross-section is largely determined by the statistical uncertainty associated with NER. In addition, a systematic unc… view at source ↗
read the original abstract

Proton capture on $^{19,20}$O nuclei is measured in inverse kinematics with the active target detector MuSIC@Indiana using CH$_4$ as the target gas. Rejection of unreacted and inelastically scattered beam, along with transfer and fusion on the $^{12}$C allows extraction of the (p,n) cross section. As the cross-section for direct (p,n) processes at these energies is small, the measurement provides access to the proton fusion cross-section. An analysis approach that allows extraction of the proton fusion cross-section is detailed.

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 a measurement of the ^{19,20}O(p,n)^{19,20}F reactions in inverse kinematics using the MuSIC@Indiana active-target detector with CH_4 gas. The central claim is that kinematic and energy-loss cuts can reject unreacted beam, inelastic scattering on the oxygen isotopes, transfer reactions, and fusion/transfer on ^{12}C, thereby isolating the (p,n) channel; because the direct (p,n) cross section is small at the relevant energies, the extracted yield is interpreted as a measure of the proton-fusion cross section. An analysis approach for performing this extraction is described.

Significance. If the background-rejection strategy can be shown to achieve high purity with well-quantified efficiency, the result would supply rare experimental constraints on proton-capture cross sections for neutron-rich oxygen isotopes at low energies, information that is relevant for both nuclear astrophysics and the study of exotic nuclei. The active-target technique itself is a recognized strength for low-cross-section measurements because it provides continuous tracking and dE/dx information.

major comments (2)
  1. [Abstract] Abstract: the statement that rejection of unreacted beam, inelastic scattering, transfer, and fusion on ^{12}C 'allows extraction' of the (p,n) cross section is load-bearing for the central claim, yet the abstract supplies no efficiency curves, simulated or measured purity estimates, or comparison to known cross sections that would demonstrate residual contamination is negligible relative to statistical uncertainty.
  2. [Abstract] The weakest assumption identified in the stress-test note—that the active-target tracking plus energy-loss and vertex cuts cleanly separate the desired (p,n) events from ^{12}C fusion/transfer and inelastic scattering without significant leakage or efficiency loss—is not addressed with quantitative validation in the provided text; without such a demonstration the extracted fusion cross section remains susceptible to systematic bias.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and for highlighting the need for clearer quantitative support in the abstract. We respond to each major comment below and will revise the manuscript to address the concerns.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the statement that rejection of unreacted beam, inelastic scattering, transfer, and fusion on ^{12}C 'allows extraction' of the (p,n) cross section is load-bearing for the central claim, yet the abstract supplies no efficiency curves, simulated or measured purity estimates, or comparison to known cross sections that would demonstrate residual contamination is negligible relative to statistical uncertainty.

    Authors: We agree that the abstract would be strengthened by a brief reference to the supporting quantitative information. In the revised manuscript we will update the abstract to note that Monte Carlo simulations and data-driven checks confirm high purity with residual contamination below statistical uncertainties, with the detailed efficiency curves and contamination estimates provided in Sections 3 and 4. revision: yes

  2. Referee: [Abstract] The weakest assumption identified in the stress-test note—that the active-target tracking plus energy-loss and vertex cuts cleanly separate the desired (p,n) events from ^{12}C fusion/transfer and inelastic scattering without significant leakage or efficiency loss—is not addressed with quantitative validation in the provided text; without such a demonstration the extracted fusion cross section remains susceptible to systematic bias.

    Authors: The manuscript already describes the kinematic, energy-loss, and vertex cuts used to isolate the (p,n) channel and presents the associated analysis approach. To make the quantitative validation more prominent, we will add a concise statement to the abstract summarizing the simulated efficiency and estimated leakage fractions. This revision will directly address the concern without changing the underlying analysis. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurement report with no derivation chain

full rationale

This is a pure experimental measurement paper describing data collection and background rejection in an active-target setup to extract (p,n) cross sections on 19,20O. The abstract and analysis description state that rejection of unreacted beam, inelastic scattering, transfer, and 12C fusion 'allows extraction' of the cross section, with the small direct (p,n) contribution then interpreted as access to proton fusion. No equations, ansatze, fitted parameters renamed as predictions, or self-citation chains appear in the provided text. The result is obtained from detector data after kinematic and energy-loss cuts; any validation of those cuts is external to the derivation itself and does not reduce the reported cross section to an input by construction. The paper is therefore self-contained as a measurement report against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The central claim rests on the assumption that background rejection is sufficient to isolate the desired channel; no free parameters, new axioms, or invented entities are introduced in the abstract.

pith-pipeline@v0.9.0 · 5630 in / 1165 out tokens · 37611 ms · 2026-05-21T17:34:46.983299+00:00 · methodology

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