The Nuclear Astrophysics Program at the CERN n_TOF Facility: Results and Perspectives

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

see attached file Referee Report

Comments for author File: Comments.pdf

Author Response

We thank the referee for his careful reading and for their useful suggestions.

 

Almost all new recommended references have been added to the text.

 

Concerning the formula

 

\begin{math} 

{dN_A\over dt} = -\sigma_A\cdot N_A + \sigma_{A − 1}\cdot N_{A − 1} 

\end{math}

 

is correctly written in the LaTex file, while the pdf conversion corrupts the formula.

 

We ask to the editor to take care of this issue.

The line number is now 173 of generated pdf file.

Reviewer 2 Report

Comments and Suggestions for Authors

see attached report1.txt

Comments for author File: Comments.txt

Author Response

We thank the referee for their suggestion that will improve the manuscript and clarify some points.

 

A discussion on the relevance of the effects of stellar enhancement and on the extrapolation of MACS at high neutron energies has been added.

For convenience these statements are reported in the following:

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However, experimental data alone are not sufficient for a full definition of the reaction rate. In fact, in a stellar environment, the high s-process temperatures imply that nuclei might be excited by the intense and energetic thermal photon bath. For nuclei with excited states at low energies (say, < 100 keV), this may result in a significant thermal population of the low-lying levels.

From experiments, we have only the cross section for nuclei in their ground state, which represent only a part of the information required to derive the stellar rate. To recover the missing information an estimation of the so called Stellar Enhanced factor (SEF), i.e. the ratio between MACS at stellar environments and at ground state, can be calculated from theory \cite{Rauscher}.

In addition, one should consider that the ground-state MACS can be calculated by folding the capture cross section with the respective thermal neutron spectrum at the s-process site. To cover all possible thermal energy ranges, cross section data should be available over a sufficiently wide neutron energy range, starting at about 100 eV and extending to about 500 keV to account for the highest temperatures reached during shell carbon burning in massive stars.

In some instances, the energy range accessible via direct experimental measurements is limited to the "resolved resonance region", which could be limited in the higher energy range.

To complement for the missed neutron energy range, it is necessary to adopt a theoretical modelling of the capture reaction process. The use of cross sections from evaluated data libraries can be adopted in most cases.

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Minor points:

Q1) The information on the activation area NEAR is quite limited. There is only a reference [16] to an arXiv paper in line 81, and there is no reference for the quasi-stellar neutron spectra in lines 561-570.

 

A1) The NEAR experimental area is operative from 2021, and full commissioning has been only recently concluded. The cited arXiv paper is now (from last week) an accepted paper on EPJ A and we will add the correct citation once available.

To report additional information a statement in the n_TOF Facility Section with a remind on the neutrons/cm2/year available at NEAR has been inserted; concerning the discussion on quasi-stellar neutron spectra proceedings of the ND2025 (Nuclear Data for Science and Technology) conference, where preliminary results have been presented, are in preparation and a reference is not yet available.

 

Q2) Fig.6: The arrow from 207Tl to 207Pb should also be shown in red colour.

A2) done, thanks for spotting the typo.  

 

Q3) Line 262: A reference is missing.

A3) reference has been fixed

 

Q4) The sentence in lines 262-264 is not clear.

A4) We rephrased the statement at lines 262-264 in order to better explain the interplay between higher neutron fluxes and minor amount of sample masses needed to perform a measurement.

 

Q5) For the non-expert reader it would be interesting to see some rough numbers for the branching between (n,g) and beta-decay, e.g. for 63Ni at the conditions of He core burning and of C shell burning

A5) The paragraph on 63Ni (section 6.1) has been rephrased. 

 

Q6) Typo in Fig.7: the half-life of 63Ni is 101 yr.

A6) Many thanks for the careful reading of all details, the typo in Fig.7 has been fixed.

 

Q7) Sec.6.2 on 79Se: For the non-expert reader it would be helpful to explain that the half-life of 79Se is very sensitive to the temperature

[B]. Otherwise, the given (laboratory) half-life of 325000 yr is typically considered as almost stable for the s-process.

A7) A sentence has been added mentioning the half-life dependence of 79Se on temperature (with the suggested reference).

 

Q8) The discussion of 26Al in Sect.10 should mention the role of the isomer in 26Al, see e.g. [C,D].

A8) A brief discussion on the role of the isomer in 26Al analysis has been added (including references).

Reviewer 3 Report

Comments and Suggestions for Authors

Referee Report — “The nuclear astrophysics program at the CERN n\_TOF facility: results and perspectives”

The manuscript presents a comprehensive review of the nuclear-astrophysics program at CERN’s n\_TOF facility. It summarizes capabilities across the three beam lines (EAR1/EAR2/NEAR), the principal detector systems (C6D6, sTED, TAC, Si telescopes), and a well-chosen set of flagship physics results: bottlenecks at N=50/82/126 (e.g., La, Ce, Pb–Bi), branching-point measurements (e.g., 63Ni, 94Nb, 151Sm, 171Tm, 204Tl), neutron sources/poisons (14N, 25Mg), BBN (7Be), cosmochronology (Re/Os), and 26Al destruction channels. The review closes with forward-looking upgrades (transmission station, quasi-stellar activation at NEAR, gas cells, and the prospective n\_ACT at the BDF/SHiP line). The breadth is impressive, and the paper would serve as a useful entry point for the community. The synthesis is timely and valuable. Highlights such as the 140Ce MACS (and its tension with stellar abundances), the 171Tm impact on Yb isotopic ratios in SiC grains, precise 14N(n,p) data, Re/Os chronometer constraints, and the 26Al(n,p)/(n,α) rates are clearly relevant for modeling. The outlook (transmission, shaped-spectrum activation at NEAR, and BDF/n\_ACT) is informative and forward-looking.

Major comments.

Fill in the stray “\[?]”. In the Branching Points section there’s a literal “\[?]” around the “minimum sample mass” line. Drop in the missing reference or delete the brackets.

Polish the abstract. A few phrases read oddly—e.g., “two of them at a different bases” should be “at different baselines,” and “provides an evidence” should be “provides evidence.” A quick language pass will fix this.

Put numbers on the superlatives. “Unprecedented accuracy” is great, but the reader needs a number. You already have some—\~2.5 % for ^14N, ^26Al up to \~150 keV, the ^140Ce MACS \~40 % higher than before. A single summary table with energy range, detector, headline result, and final uncertainty would make those wins pop.

Check the figures. Make sure every figure you cite (1–10) is actually there, and that the captions say what the axes/baselines are. A simple diagram that labels each n\_TOF result by astrophysical “use-case” (bottleneck, branch point, etc.) would also help newcomers.

Explain the ^140Ce tension a bit more. It’s interesting that the new MACS pulls even further away from stellar data. Could you say which stars / metallicities are most affected and mention any systematic checks (sample purity, detector n-sensitivity) to head off confusion?

Numbers for the upgrades. The transmission station and shaped spectra at NEAR sound exciting. Even rough estimates of the expected ΔE/E, kT ranges, and fluxes would help readers judge the impact. Same for n\_ACT at the BDF—how does its flux stack up against EAR2/NEAR?

Reference list tidy-up. A few entries have typos or odd formatting—Bao et al.’s classic MACS compilation shows up as 2020, some NIM and PRC entries have volume/page glitches, and “Garcia Infances” is missing the accent. A quick sweep should catch these.

Minor/editorial comments.

Word choice/typos: “different bases” → “different baselines”; “an evidence” → “evidence".
Acronyms: ensure first-use expansions (e.g., TAC, sTED) and that all acronyms appear in the Abbreviations list.
Status tags: when discussing specific cases (e.g., 79Se preliminary), state the status explicitly (published vs. preliminary), and consider a superscript “(prelim.)”.
Tables: consider adding an “Astrophysical role” column (bottleneck/branch/poison/source/BBN/chronometer) to help readers connect measurements to impact.

Recommendation.

The scientific content and selection of results are strong. Addressing the points above will substantially improve clarity, traceability, and long-term reference value. Subject to satisfactory revision, the manuscript would make an excellent, citable overview appropriate for publication in Universe MDPI.

Comments on the Quality of English Language

See the report above.

Author Response

We thank the referee for their suggestions which will improve the manuscript and result in a better presentation.

 

In the following the list of applied changes:

Major comments.

 

Fill in the stray “\[?]”. In the Branching Points section, there’s a literal “\[?]” around the “minimum sample mass” line. Drop in the missing reference or delete the brackets.

-> the reference link has been fixed

 

Polish the abstract. A few phrases read oddly—e.g., “two of them at a different bases” should be “at different baselines,” and “provides an evidence” should be “provides evidence.” A quick language pass will fix this.

-> The suggestions have been considered and the abstract partially rephrased.

 

Put numbers on the superlatives. “Unprecedented accuracy” is great, but the reader needs a number. You already have some—\~2.5 % for ^14N, ^26Al up to \~150 keV, the ^140Ce MACS \~40 % higher than before. A single summary table with energy range, detector, headline result, and final uncertainty would make those wins pop.

-> Numbers have been added to the text (enrichment of 140Ce sample, MACS extracted with uncertainties lower than 5%, ...) Table 1 and 2 have been deeply updated to insert information on physics case of single measurements, measured energy ranges and detectors used.

We thank the referee, the suggestion to enlarge these tables improve the report on performed activity.

 

Check the figures. Make sure every figure you cite (1–10) is actually there, and that the captions say what the axes/baselines are. A simple diagram that labels each n\_TOF result by astrophysical “use-case” (bottleneck, branch point, etc.) would also help newcomers.

-> Text and figure captions have been checked once more.

 

Explain the ^140Ce tension a bit more. It’s interesting that the new MACS pulls even further away from stellar data. Could you say which stars / metallicities are most affected and mention any systematic checks (sample purity, detector n-sensitivity) to head off confusion?

-> More information of involved stars has been inserted in the text (stars with mass lower than 2 solar masses and present in the Galactic disk).

The enrichment of the used sample has also reported.

The low neutron sensitivity aspect was deeply debugged in the in-house developed C6D6 detectors.

 

Numbers for the upgrades. The transmission station and shaped spectra at NEAR sound exciting. Even rough estimates of the expected ΔE/E, kT ranges, and fluxes would help readers judge the impact. Same for n\_ACT at the BDF—how does its flux stack up against EAR2/NEAR?

-> Future upgrades in dedicated chapter have been enumerated.

A comparison of NEAR and n_ACT has been reported, mainly focusing on neutron fluxes.

 

Reference list tidy-up. A few entries have typos or odd formatting—Bao et al.’s classic MACS compilation shows up as 2020, some NIM and PRC entries have volume/page glitches, and “Garcia Infances” is missing the accent. A quick sweep should catch these.

-> we revised the reference list fixing typos and formatting

 

Minor/editorial comments.

Word choice/typos: “different bases” → “different baselines”; “an evidence” → “evidence".

Acronyms: ensure first-use expansions (e.g., TAC, sTED) and that all acronyms appear in the Abbreviations list.

Status tags: when discussing specific cases (e.g., 79Se preliminary), state the status explicitly (published vs. preliminary), and consider a superscript “(prelim.)”.

Tables: consider adding an “Astrophysical role” column (bottleneck/branch/poison/source/BBN/chronometer) to help readers connect measurements to impact.

 

-> all minor comments have been considered.