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arxiv: 2606.02266 · v1 · pith:KMH7MTBVnew · submitted 2026-06-01 · ⚛️ nucl-ex · nucl-th

Studies of rm ^(144,148)Sm+α potential for the p-process nucleosynthesis

C. Soto , C. Ducoin , N. Millard-Pinard , B. M. Rebeiro , O. St\'ezowski , N. de S\'er\'eville , F. Hammache , A. Chalil
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Y. Demane C. Bachelet J.-C. Thomas M. Assi\'e M. Benhatchi V. Girard-Alcindor S. V. Harissopulos H. Jacob A. Lagoyannis S. Morard S. Nandi J. P\'epin L. Perrot A. M. S\'anchez-Ben\'itez I. Stefan T. Zanatta-Martinez
This is my paper

Pith reviewed 2026-06-28 11:48 UTC · model grok-4.3

classification ⚛️ nucl-ex nucl-th
keywords alpha optical model potentialp-process nucleosynthesissamarium isotopeselastic scatteringisotopic effectsalpha capture cross sectionsphotodisintegration
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The pith

Including isotopic effects in the alpha optical model potential for samarium multiplies the (α,γ) cross section ratio by up to a factor of two.

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

The study measures alpha elastic and inelastic scattering on 148Sm and compares the results to existing data on 144Sm. These measurements reveal isotopic differences in the alpha-nucleus optical model potential. The differences alter the calculated alpha-induced reaction cross sections at low energies relevant to the p-process. When the isotopic variations are included, the ratio of (α,γ) cross sections between the two isotopes increases by as much as a factor of two. Accurate ratios matter because they influence branching in nucleosynthesis networks that produce p-nuclei.

Core claim

New experimental data on α elastic and inelastic scattering on 148Sm, combined with prior data on 144Sm, show that isotopic effects in the α optical model potential multiply the isotopic ratio for (α,γ) cross sections by up to a factor of two at astrophysical energies.

What carries the argument

The α optical model potential (AOMP) parametrized from elastic scattering distributions and extrapolated to compute low-energy reaction cross sections.

If this is right

  • Alpha photodisintegration rates in p-process networks for these samarium isotopes must incorporate the isotopic AOMP variations.
  • Branching points in the reaction networks at alpha capture or photodisintegration steps shift for 144Sm and 148Sm.
  • Abundance predictions for p-nuclei near mass 144-148 change when the adjusted cross section ratios are used.
  • Extrapolations of AOMP parameters to astrophysical energies must treat each isotope separately rather than assuming a common form.

Where Pith is reading between the lines

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

  • Direct low-energy (α,γ) measurements on these isotopes would test whether the extrapolated potentials hold.
  • Comparable isotopic studies on other p-nucleus pairs could reveal similar ratio adjustments in reaction networks.
  • Updated rates could be inserted into full nucleosynthesis simulations to check effects on final p-nuclei yields.

Load-bearing premise

The optical model potential parameters fitted to scattering data at higher energies remain valid when extrapolated to the much lower astrophysical energies.

What would settle it

A direct measurement of (α,γ) cross sections on both 144Sm and 148Sm at energies below 10 MeV that finds their ratio does not increase by a factor of two when the isotopic potential is used.

Figures

Figures reproduced from arXiv: 2606.02266 by A. Chalil, A. Lagoyannis, A. M. S\'anchez-Ben\'itez, B. M. Rebeiro, C. Bachelet, C. Ducoin, C. Soto, F. Hammache, H. Jacob, I. Stefan, J.-C. Thomas, J. P\'epin, L. Perrot, M. Assi\'e, M. Benhatchi, N. de S\'er\'eville, N. Millard-Pinard, O. St\'ezowski, S. Morard, S. Nandi, S. V. Harissopulos, T. Zanatta-Martinez, V. Girard-Alcindor, Y. Demane.

Figure 1
Figure 1. Figure 1: (a) Sketch of the experimental setup illustrating the Split-Pole spectrometer [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Identification plots of the reaction channels measured for a 20 MeV [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: RBS spectrum for the central point of the [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Elastic angular distribution: experimental data by Mohr [PITH_FULL_IMAGE:figures/full_fig_p012_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Similar to Figure 4, with standard AOMP models [PITH_FULL_IMAGE:figures/full_fig_p015_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Left: TALYS prediction for the elastic cross-section ratio [PITH_FULL_IMAGE:figures/full_fig_p016_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Similar to Figure 6, with AOMP models fitted to [PITH_FULL_IMAGE:figures/full_fig_p017_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: TALYS prediction for the elastic cross-section ratio [PITH_FULL_IMAGE:figures/full_fig_p018_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Left: differential cross section of α inelastic scattering to the first level of 148Sm for different AOMP, in the DWBA approach. Right: ratio to elastic differential cross section, with experimental data from this work. tings. We show in [PITH_FULL_IMAGE:figures/full_fig_p019_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Impact of coupling scheme (R1, R2, V 1, V 2, see text) for two AOMP (aop6 and aop2-Bb). The DWBA curves are also shown (bold line). Left: differential cross section of α inelastic scattering on the first level of 148Sm. Right: ratio to elastic differ￾ential cross section, with experimental data from this work. reproduction of the experimental data, and hinders the sensitivity to the AOMP model. We further… view at source ↗
Figure 11
Figure 11. Figure 11: Inelastic ratio: impact of the deformation parameter used in rotational cou [PITH_FULL_IMAGE:figures/full_fig_p022_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: S-factor of 144Sm(α, γ) 148Gd in the astrophysical energy range (∼ 5 to 12 MeV) extended to the energy range of experimental data from Somorjai-1997 [9]. Left: standard AOMP models. Middle: effect of the fit of aop2 and aop9 to Mohr-1997 (α, α) data. Right: effect of parameter energy dependence (-E) or sharp imaginary part (-SI); see text for details. right part, we focus on modifications made to aop2 and… view at source ↗
Figure 13
Figure 13. Figure 13: Capture cross section isotopic ratio. Left: standard AOMP models. Some [PITH_FULL_IMAGE:figures/full_fig_p024_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Similar to Figure 13 in the case of [PITH_FULL_IMAGE:figures/full_fig_p025_14.png] view at source ↗
read the original abstract

Nucleosynthesis reaction networks leading to $p$-nuclei involve a combination of different types of photodisintegration and capture reactions, as well as $\beta^+$ decays or electron captures. Photodisintegration reactions involving $\alpha$ particles present a particular interest as they serve as branching points of the reaction networks. The cross sections of these reactions depend crucially on the $\alpha$-nucleus interaction. The $\alpha$ optical model potential (AOMP) is determined mostly by means of experimental differential elastic scattering distributions. Several previous studies have focused on the case of $\rm ^{144}Sm$, an intriguing $p$-nucleus that is semi-magic with 82 neutrons. This work presents new experimental data on $\alpha$ elastic and inelastic scattering on $\rm ^{148}Sm$, its closest stable isotope. Isotopic effects on the description of the AOMP are studied, as well as their consequences on the prediction of $\alpha$-induced reaction cross sections at astrophysical energies. It is shown that the isotopic ratio for $(\alpha,\gamma)$ cross sections can be multiplied up to a factor of two when these effects are included.

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

1 major / 2 minor

Summary. The manuscript reports new experimental measurements of α elastic and inelastic scattering on 148Sm, constrains the α-nucleus optical model potential (AOMP) from these data, examines isotopic differences relative to prior 144Sm results, and concludes that inclusion of these isotopic effects can alter the predicted 144Sm/148Sm (α,γ) cross-section ratio by up to a factor of two at astrophysical energies relevant to p-process nucleosynthesis.

Significance. If the low-energy extrapolation of the AOMP holds, the result demonstrates that isotopic variations in the potential can produce order-unity changes in key (α,γ) rates, which would affect branching points in p-process networks. The new scattering data themselves constitute a useful addition to the experimental database for AOMP studies.

major comments (1)
  1. [Section discussing (α,γ) predictions at astrophysical energies] The central claim that the isotopic ratio for (α,γ) cross sections can change by a factor of two rests on the validity of AOMP parameters fitted at the measured (higher) scattering energies when extrapolated to the much lower energies that govern p-process rates. No independent low-energy anchor (e.g., existing (α,γ) or (α,n) data on either isotope) is invoked to test whether the isotopic variation survives this extrapolation, where the imaginary part of the potential is poorly constrained by the Coulomb barrier.
minor comments (2)
  1. [Abstract] The abstract states a quantitative factor-of-two claim without reference to the precise energies, data quality, fitting procedure, or uncertainties; these details should be summarized to allow readers to assess the support for the result.
  2. Clarify the range of laboratory energies at which the new 148Sm scattering data were acquired and the precise functional form and free parameters of the AOMP used in the fits.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comment. We address the major comment below.

read point-by-point responses

  1. Referee: [Section discussing (α,γ) predictions at astrophysical energies] The central claim that the isotopic ratio for (α,γ) cross sections can change by a factor of two rests on the validity of AOMP parameters fitted at the measured (higher) scattering energies when extrapolated to the much lower energies that govern p-process rates. No independent low-energy anchor (e.g., existing (α,γ) or (α,n) data on either isotope) is invoked to test whether the isotopic variation survives this extrapolation, where the imaginary part of the potential is poorly constrained by the Coulomb barrier.

    Authors: We agree that the extrapolation of the AOMP to astrophysical energies carries uncertainties, especially regarding the imaginary part, which is less constrained below the Coulomb barrier, and that no direct low-energy (α,γ) or (α,n) data exist for these isotopes to provide an independent anchor. The isotopic differences we report are driven by the elastic scattering angular distributions measured at higher energies, which constrain the real part of the potential; the imaginary part follows standard parametrizations used in the literature. Our analysis explores the sensitivity to reasonable variations in the imaginary potential. While direct low-energy anchors would be desirable, they are unavailable, and the extrapolation method is the standard approach in AOMP studies for p-process applications. We will revise the manuscript to add an explicit discussion of these extrapolation uncertainties and their implications for the predicted isotopic ratio. revision: partial

Circularity Check

0 steps flagged

No significant circularity; derivation uses new scattering data to fit AOMP then computes cross-section ratios

full rationale

The paper presents new elastic/inelastic scattering data on 148Sm, fits standard optical-model parameters to those data, and then uses the resulting potentials (compared against prior 144Sm fits) to compute (α,γ) cross sections at astrophysical energies. The reported factor-of-two change in the isotopic ratio is an output of that forward calculation rather than a quantity defined into the fit or recovered by construction. No load-bearing step reduces to a self-citation, an ansatz smuggled via prior work, or a fitted input relabeled as a prediction. The central claim therefore remains independent of its inputs.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim depends on the standard alpha optical model formalism and its extrapolation to low energies; specific parameter values and any additional assumptions are not stated in the abstract.

free parameters (1)
  • AOMP parameters (depths, radii, diffuseness)
    Parameters of the alpha optical model potential are adjusted to fit the new scattering data.
axioms (1)
  • domain assumption The optical model potential fitted at measured energies can be extrapolated to astrophysical energies.
    This extrapolation is required to connect the scattering data to p-process reaction rates.

pith-pipeline@v0.9.1-grok · 5886 in / 1247 out tokens · 26417 ms · 2026-06-28T11:48:13.141829+00:00 · methodology

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