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REVIEW 3 major objections 6 minor 44 references

Measurement of neutron induced reaction cross-section of tantalum with covariance analysis

T0 review · 3 major / 6 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read This paper measures the 181Ta(n,γ)182Ta reaction cross-section at four neutron energies and, for the first time for this reaction, reports a full covariance matrix for the results.

desk verdict Solid activation measurement with a useful covariance analysis; the printed timing-factor formula has a typo, but the stress-test's quantitative alarm is itself arithmetic. read the letter →

arxiv 2412.18422 v1 pith:DMYXMRAL submitted 2024-12-24 nucl-ex

Mahima Upadhyay , Mahesh Choudhary , Namrata Singh , Punit Dubey , Shweta Singh , Sriya Paul , Utkarsha Mishra , G. Mishra
show 7 more authors
G. Mohanto Sukanya De L. S. Danu B. Lalremruata Ajay Kumar R. G. Thomas A. Kumar
This is my paper · ORCID
classification nucl-ex PACS 25.40.Lw29.30.Kv
keywords neutroncapturecross-sectiontantalum-181offlinegamma-rayspectroscopycovarianceanalysisactivation7Li(pn)sourcemonitorreactionlevel-densitymodels
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper reports a new measurement of the neutron-capture cross-section of tantalum-181 at four neutron energies from 1.37 to 3.05 MeV, using activation and offline gamma-ray spectroscopy. The measured values are 123.94, 82.62, 57.23, and 48.12 mb, with total uncertainties of 8–10% and with pairwise correlation coefficients between the points. For the first time for this reaction, the uncertainties are propagated through a full covariance analysis, giving users of nuclear data the information needed to combine these points with other measurements. The measurement matters because tantalum is used in reactor design, fusion technology, and medical applications, and the existing data in this energy range lacked quantified correlations.

What carries the argument

The measurement uses a ratio method: the target cross-section is derived from the monitor reaction cross-section, 115In(n,n'γ)115mIn from an evaluated library, multiplied by measured ratios of gamma-ray counts, timing factors, atom numbers, and a low-energy background correction ratio. The neutron flux used to average the monitor cross-section and to compute the background correction comes from a simulation code that generates the 7Li(p,n0) and 7Li(p,n1) spectra; a separate Monte Carlo program provides the gamma-ray efficiency for the sample geometry and the coincidence-summing corrections. Covariance propagation follows a published method to turn the uncertainties in counts, efficiency, monitor cross-section, timing, and atom numbers into the final correlation matrix.

What would settle it

A time-of-flight measurement of the 7Li(p,n) neutron spectrum at proton energies 3.3, 4.0, 4.5, and 5.0 MeV, or a reanalysis of the same activations using a different evaluated shape for the 181Ta(n,γ) cross-section in the low-energy background correction, would show whether the reported cross-sections shift beyond their quoted uncertainties.

Watch

Extended reading notes

Core claim

The central claim is that the spectrum-averaged 181Ta(n,γ)182Ta cross-section is 123.94 ± 10.42 mb at 1.37 ± 0.13 MeV, 82.62 ± 7.04 mb at 2.06 ± 0.14 MeV, 57.23 ± 4.95 mb at 2.56 ± 0.15 MeV, and 48.12 ± 4.76 mb at 3.05 ± 0.17 MeV, with correlation coefficients ranging from 0.078 to 0.104. The paper argues that these are the first data for this reaction to carry a complete covariance matrix, so the uncertainties can be propagated correctly when the points are used in evaluations or applications. The measured trend agrees best with the ENDF/B-VIII.0 evaluation and with the constant-temperature Fermi-gas level-density model among the six TALYS model variants tested.

Load-bearing premise

The results stand or fall on the simulated neutron spectrum from the EPEN code, which is not independently checked by time-of-flight, and on the use of an evaluated cross-section shape for the very reaction being measured to subtract low-energy background neutrons.

Editorial extensions

If this is right

  • The energy-dependent trend of 181Ta(n,γ) cross-sections from 1.37 to 3.05 MeV is now pinned down by data with 8–10% total uncertainty, narrower than the evaluated monitor uncertainty used in the analysis.
  • Users of nuclear data can now combine these four points with previous measurements using the reported correlation matrix rather than treating them as independent.
  • The measured points favor the ENDF/B-VIII.0 evaluation and the constant-temperature Fermi-gas level-density model, while the other five TALYS level-density models underpredict the cross-section at the two higher energies.
  • The 1.37 MeV point is consistent with the spread of the TALYS level-density models, adding a constraint in a region where older experimental points scatter widely.
  • The reported correlations, though small, are non-negligible for evaluations and should be preserved when these data enter a least-squares adjustment.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the simulated neutron spectrum is validated by a future time-of-flight measurement, the same analysis procedure could be re-run to produce finer-binned or differential cross-sections rather than spectrum-averaged points.
  • The same covariance framework could be applied to other reactions measured in the same irradiation campaign, yielding a self-consistent set of correlated cross-sections for reactor materials.
  • Because the low-energy background correction uses the shape of the targeted cross-section below 1 MeV, these data carry indirect constraints on the sub-MeV capture shape that could be tested by a dedicated measurement.
  • A least-squares evaluation of tantalum capture data that includes the reported correlation matrix would shift the evaluated uncertainties compared with treating the four points as independent.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 6 minor

Summary. The paper reports new measurements of the 181Ta(n,γ)182Ta reaction cross-section at four neutron energies (1.37, 2.06, 2.56, 3.05 MeV) using the activation technique with offline γ-ray spectroscopy at the FOTIA facility. Neutrons are produced by 7Li(p,n)7Be and the flux spectrum is calculated with the EPEN code. The 115In(n,n'γ)115mIn reaction is used as the monitor, and the analysis includes corrections for the low-energy (p,n1) background, coincidence summing, and a full covariance propagation. The resulting cross-sections and their correlation matrix are compared with EXFOR data, evaluated libraries, and TALYS-1.96 calculations with six level-density models.

Significance. If the results are correct, the four data points with a complete correlation matrix are a useful addition to the sparse 181Ta capture data around 1–3 MeV, and the explicit covariance propagation is a good practice example for activation measurements. The paper is built on standard activation formulae, provides a detailed uncertainty budget, and includes a clear presentation of the correction factors. However, the central numbers are currently not fully verifiable: Eq. (7) as printed is not the standard activation timing factor, and the low-energy background correction in Eq. (5) is library-dependent without a propagated uncertainty. These issues are local and fixable, so the manuscript deserves a major revision rather than rejection.

major comments (3)
  1. [Section 3.4, Eq. (7)] The printed timing factor is not the standard activation formula. With t_u defined as counting time and t_w as cooling time, the standard expression is f = (1−e^{−λt_i}) e^{−λt_w} (1−e^{−λt_c})/λ, not (1−e^{−λt_i}) e^{−λt_u} (1−e^{−λt_w})/λ. For the 115mIn monitor (T½ = 4.486 h) and the times in Table 2, the printed formula overestimates f_m by factors of about 39.2, 2.95, 2.55, and 14.7 at 1.37, 2.06, 2.56, and 3.05 MeV, respectively. Since f_m appears in the numerator of Eq. (6), using the printed formula would inflate the derived cross-sections by those factors, far beyond the quoted 8–10% uncertainties. The authors must state explicitly which expression was used in the analysis; if Eq. (7) is a typographical error, it must be corrected and the authors must confirm that Table 10 is unaffected and reproduce the calculation with the standard formula.
  2. [Section 3.3, Eq. (5), Table 8] The low-energy background correction Lcor is evaluated using σx taken from the IRDFF-1.05 library for the same 181Ta(n,γ) reaction being measured. The correction is therefore not a purely experimental subtraction; any error in the shape of the evaluated cross-section inside the (p,n1) neutron-energy range propagates directly into the final result through the ratio Lcor(t)/Lcor(m). Moreover, Table 9 does not list Lcor as an uncertainty component and Section 3.5 does not propagate its uncertainty. Since Lcor(t) ranges from 0.854 to 0.912 and the net ratio Lcor(t)/Lcor(m) differs from unity by about 3–9%, this omitted uncertainty can be comparable to the total quoted uncertainties. The authors should estimate and propagate the uncertainty of Lcor, or justify quantitatively that it is negligible.
  3. [Sections 2.1 and 3.2, Eq. (2)] The neutron flux spectrum is taken solely from the EPEN simulation and is not checked by an independent experimental method such as time-of-flight. The monitor-averaged cross-section in Eq. (2) and the derived results depend on the spectral shape of the (p,n0) component, and the FWHM-based energy uncertainty quoted in Section 2.1 is not an uncertainty on the spectral shape. The covariance analysis contains no contribution from spectral-shape uncertainty. Please provide a sensitivity test, for example by varying the simulated spectrum within plausible limits, to demonstrate that the reported cross-sections and uncertainties are robust, or include a spectral-shape systematic error in the covariance matrix.
minor comments (6)
  1. [Section 3.4] The sentence following Eq. (7) defines t_u as counting time and t_w as cooling time, which is opposite to the standard notation; please correct the definitions or the equation.
  2. [Section 3.2, Eq. (4)] The summation index l is reused as the label for the neutron-energy set; please use distinct symbols for the summation indices (for example i and j) to avoid ambiguity.
  3. [Table 6] The correlation-matrix entries in Table 6 are not visually aligned with the group boundaries and labels, making it difficult to verify the matrix; please reformat the table, for example by separating the groups and adding clear column headers.
  4. [Section 2.1, Eq. (1)] The text says 'The integration limits for the proton energies' but the integrals in Eq. (1) are over neutron energy; please correct the wording.
  5. [Section 5] The sentence 'All prior experimental results have large inconsistencies with the present measured cross-sections' is too strong given Figure 3, where several previous data points lie within 30–50% of the present results; please rephrase to reflect the actual scatter.
  6. [References] Reference [19] appears to be the JENDL-4.0 publication (Shibata et al., 2011); the JENDL-5 evaluation should be cited as O. Iwamoto et al., J. Nucl. Sci. Technol. 60 (2023) 1–13.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the Ta cross-section is count-ratio based; the IRDFF-based low-energy correction and self-citations are method inputs, not constructed equivalences.

full rationale

Section 3.4's Eq. (6) obtains <σt> from measured gamma counts, atom numbers, efficiencies, intensities, timing factors, and the IRDFF-1.05 monitor cross-section; no Ta cross-section parameter is fitted to the Ta data. The low-energy background correction Eq. (5) does use the IRDFF-1.05 181Ta(n,γ) cross-section as σx for the target, so the final value carries some sensitivity to that evaluation's shape, but Lcor is a multiplicative correction (0.85–0.91) and the reported values are still dominated by the measured count ratio; this is a standard activation-data correction and not an equivalence-by-construction. Citations of the EPEN code [22] and of the authors' earlier coincidence-summing paper [29] are methodological; they are not invoked as a uniqueness proof or as a fitted input that forces the result. A separate, non-circularity issue is that Eq. (7) appears to interchange cooling and counting times; if that equation were used as written the results would be wrong, but this is an internal-error concern, not a circular-derivation concern. Overall the derivation chain is self-contained against external benchmarks, so the circularity score is 0.

Assumptions & free parameters 1 free parameters · 3 assumptions · 0 invented entities

The paper introduces no new entities. The central claim rests on the assumed validity of the EPEN simulation, the IRDFF monitor and target cross-section shapes, and the calibration corrections. The only fitted numbers are the efficiency curve parameters, which are standard but not reported.

free parameters (1)
  • Efficiency curve fit parameters = not stated
    Three parameters fitted to 152Eu calibration data are used to interpolate detector efficiency at the gamma energies of interest; their values are not reported, only the resulting efficiencies and correlations.
assumptions (3)
  • domain assumption The EPEN code accurately simulates the neutron energy spectrum from 7Li(p,n) including (p,n0) and (p,n1) components.
    Section 2.1; time-of-flight was not available, so the flux shape and average energies come entirely from this simulation.
  • domain assumption IRDFF-1.05 provides the true monitor cross-section for 115In(n,n'γ)115mIn and the correct cross-section shape for 181Ta(n,γ) for the low-energy correction.
    Sections 3.2 and 3.3; the monitor provides the flux scale, and Eq. (5) uses the Ta cross-section from the same library, creating partial circularity.
  • domain assumption The efficiency calibration and EFFTRAN corrections for coincidence summing and geometry transfer are valid.
    Section 3.1; the detector efficiency at 1121 keV and 336 keV is interpolated from a 152Eu fit and corrected by Monte Carlo simulation.

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Pith. "Pith review of Measurement of neutron induced reaction cross-section of tantalum with covariance analysis." pith.science (2026). https://pith.science/paper/DMYXMRAL

@misc{pith2026241218422,
  author       = {Pith},
  title        = {Pith review of: Measurement of neutron induced reaction cross-section of tantalum with covariance analysis},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/DMYXMRAL}},
  note         = {Machine review of arXiv:2412.18422}
}
abstract

The current study presents the cross-section measurement of $^{181}$Ta(n,$\gamma$)$^{182}$Ta reaction at 1.37 $\pm$ 0.13, 2.06 $\pm$ 0.14, 2.56 $\pm$ 0.15, and 3.05 $\pm$ 0.17 MeV neutron energies utilizing offline $\gamma$-ray spectroscopy. The neutrons were generated through the $^{7}$Li(p,n)$^{7}$Be reaction. The $^{115}$In(n,n'$\gamma$)$^{115m}$In reaction served as a monitor reaction. The covariance analysis was used to quantify the uncertainties in the measured cross-sections for the first time for the $^{181}$Ta(n,$\gamma$)$^{182}$Ta reaction. The present study provides detailed information on the propagation of uncertainty in the overall result. The required corrections for low energy background neutron and $\gamma$-ray coincidence summing effect have been made in the present measurement. The output is compared with the pre-existing cross-section data from the EXFOR database, evaluated data libraries and theoretical model predictions.

Figures

Figures reproduced from arXiv: 2412.18422 by the authors.

Figure 1
Figure 1. Neutron flux for (p,n0) and (p,n1) generated from EPEN code for Ep = 3.3 ± 0.02, 4.0 ± 0.02, 4.5 ± 0.02, 5.0 ± 0.02 MeV. the weight of the sample are briefly provided in [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Interpolated efficiencies of the detector [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Cross-section of 181Ta(n,γ) 182Ta reaction studied in the present work compared with different level density models, EXFOR database and different evaluated data libraries [PITH_FULL_IMAGE:figures/full_fig_p012_3.png] view at source ↗

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