Antiprotonic Atoms as Gateways to HCI

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

There are some typos, in particular references appear as "?" in the text. These may be fixed at proof level, however.

Author Response

Reviewer Comment:
There are some typos, in particular references appear as "?" in the text. These may be fixed at proof level, however.

Author Response:
Thank you for your careful reading. We have corrected the typos and resolved the reference issues in the revised manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript with the title "Antiprotonic atoms as a gateway to HCI" by Lidia Lappo and Georgy Kornakov presents original results on the creation of HCI and on the creation of nuclear fragments via the creation of antiprotonic atoms followed by de-excitation and annihilation. The presented results are based on simulations performed using the GEANT4 toolkit, they are original and they merit publication, however their presentation needs improvements.

The manuscript has 3 main logical parts:

The first part contains Section 1 and Section 2, in which the presentation of the antiprotonic atoms and their creation in a nested Penning trap is presented.

In the second part (Section 3 and 4) the details of the GEANT4 simulations are presented along with presentation of the results on the nuclear fragment production.

In the last part (Section 5) the algorithm is presented, which allows the selection of the best parent nuclei for the production of a selected nuclear fragment.

The logical connection between the first part and last two parts is week, namely, it is not clear for the reader how the geometry used during the GEANT4 simulation integrates with the experimental setup suggested in the first part. The connection between the suggested experimental setup and the simulation geometry should be emphasized in the manuscript.

Beside this general comment I would like to point out a few more punctual issues with the manuscript, which needs improvements:

1) There is a typo in the title of the manuscript: Antiptotonic -> Antiprotonic

2) In section 1, formulas 1,2,3 are valid/exact for a single antiproton bound to a nuclei. In the case of antiprotonic atoms, where beside the antiproton there also electrons bound to the nuclei thei are only order of magnitude estimates. This should be stated in the manuscript.

3) Page 2, line 30: type: Bhor -> Bohr

4) Figure 2 shows the spectra of gamma photons produced during the de-excitation and annihilation of the antiprotonic I125. These photons are originating either the de-excitation or annihilation. It would be useful if on the figure the source of each peak would be indicated (ex. bu using different colors for the de-excitation and the annihilation photons).

5) Page 3, lines 64-69, a more detailed presentation of the pulsed production of antihydrogen atoms would be useful for the reader.

6) line 72: "ions" -> "atoms" the reaction takes place between the antiproton and a atom in a Rydberg state.

7) line 89: the message of the first sentence in section 2.1 is lost...please rephrase..

8) Comments regarding the presentation of the simulation geometry:
    
    8a) It is not clear for the reader if the target isotopes are placed on the surface of the sphere (this is my guess) or they are distributed inside the spherical a body. this should be clarified explicitly in the manuscript. Regardless which case is valid, in the manuscript details about the density  (and the thickness of the isotope layer) of the target isotopes should be specified. 

    8b) The antiprotons are placed/generated in the middle of the sphere with 1 keV kinetic energy. It should be commented why this energy is used....the antiproton capture cross section is projectile velocity dependent. Does the obtained results depend on the initial energy of the antiprotons?

    8c) Please comment on how this geometry can be realized experimentally

9) Page 9, line 224: In the manuscript Dijkstra's algorithm is mentioned ....please include here a reference

10) In section 5 it is not clearly stated the origin of the data which is used to construction the reaction graph (nodes - isotope and links - frequencies). Is this data extracted from literature or it is extracted from the GEANT4 simulation data. Based on the summary presented in section 6, my guess is that it is extracted from the GEANT4 simulations, but this should be stated explicitly in the manuscript.

11) From Figure 9 and 10 the legend is missing, and it also not clear (it is not stated in the body of the manuscript or in the figure captions) what quantity is represented on the heat maps.   


12) page 9, line 244: typo: "Z from B" -> "X from B"

13) page 12, line 267-268: It is not clear for the reader how the presented results show information about the structure of atomic nuclei.....

14) The authors state that simulation are performed for isotopes with atomic number less than 100, but from these date is shown only for a few selected case. Is the full simulation data set available for the public? If yes, a reference to it should be included into the manuscript.    



Based on the above observations, I recommend the publication of the manuscript after major revisions are done.

Author Response

Reviewer Comment 1, 3, 12:

1. There is a typo in the title of the manuscript: Antiptotonic → Antiprotonic

2. Page 2, line 30: typo: Bhor → Bohr

3. Page 9, line 244: typo: Z from B → X from B

Response:
Thank you for pointing out these typos. They have all been corrected in the revised manuscript.

Reviewer Comment 2:
In Section 1, formulas (1–3) are exact for a single antiproton bound to a nucleus. In the presence of bound electrons, as in antiprotonic atoms, they are only order-of-magnitude estimates.

Response:
We agree, and this clarification has been added to the manuscript. The revised text emphasizes that these formulas aren't precise due to the influence of electrons.

Reviewer Comment 4:
It would be useful if Figure 2 indicated which peaks originate from de-excitation vs. annihilation.

Response:
We appreciate the suggestion. Unfortunately, GEANT4 does not allow us to distinguish directly the origin of each photon (de-excitation vs. annihilation). However, to aid interpretation, we have added calculated de-excitation photon energies as reference markers in Figure 2.

Reviewer Comments 5, 6, 7:
5) A more detailed description of pulsed antihydrogen production would help.
6) Line 72: "ions" → "atoms"
7) Line 89: The first sentence in Section 2.1 is unclear.

Response:
Thank you for these observations. The relevant sections have been revised and rephrased for clarity, including correction of the "ions" → "atoms" error. We hope the discussion is now clearer for the reader.

Reviewer Comment 8a:
Clarify whether the target isotopes are placed on the surface or within the sphere, and specify their density and thickness.

Response 8a:
Thank you for the comment. We clarified that the detector is modeled as a thin (0.5 nm) sphere entirely composed of a single isotope. The isotope material is defined individually via a script to allow easy substitution. These details have been added to Section 3.

Reviewer Comment 8b:
Why was 1 keV energy chosen for the antiprotons? Does the result depend on this?

Response 8b:
We used 1 keV as it is the lowest energy for antiprotons supported reliably in GEANT4. The results do depend on antiproton energy, and this was chosen to mimic the very low-energy conditions expected in the experiment. A comment on this has been added to the manuscript.

Reviewer Comment 8c:
Please comment on how this geometry can be realized experimentally.

Response 8c:
We clarified in the text that the simulated geometry is not meant to represent a physical setup but serves as a conceptual model to evaluate fragment distributions from antiproton annihilation. The experimental geometry will differ.

Reviewer Comment 9:
Include a reference for Dijkstra's algorithm.

Response 9:
A reference for Dijkstra’s algorithm has been added to the manuscript.

Reviewer Comment 10:
Clarify the source of the data used to construct the reaction graph.

Response 10:
The data for constructing the reaction graph (nodes and links) was extracted from the GEANT4 simulations. This is now explicitly stated in Section 5.

Reviewer Comment 11:
Figures 9 and 10 lack legends, and it is unclear what the heat maps represent.

Response 11:
Legends and clarifying information have been added to Figures 9 and 10, and the captions have been updated accordingly to indicate what quantities are shown.

Reviewer Comment 13:
It is not clear how the presented results provide information about nuclear structure.

Response 13:
We agree. The sentence in question has been removed to avoid misleading implications.

Reviewer Comment 14:
Only a subset of simulation results is shown. Is the full dataset available?

Response 14:
The full simulation dataset is not publicly available; however, the simulations can be reproduced using the provided physics lists and descriptions. A comment to this effect has been added to the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

This article reports a method to produce highly charged ions through antiprotonic atoms.  While the method is pretty novel, the experimental verification is challenging and might not be possible for some years. Nevertheless, this idea is worth publishing. However, this article should be improved in presentation.

Following are some specific comments.

1. In the main text, all the references are shown as [?].

2. The first sentence of the abstract is finished with "atomic nuclear structures", which is quite ambiguous. Do you mean atomic and nuclear structure, or what else?

3. In line 20, "negative particles" should be "anti-particles"?

4. The two sentences in lines 80 and 81 are replication of sentences above.

5. Line 101, p^- should be p-bar?

6. Line 107, "single negative particle" should be specified. Does it mean antiproton?

Author Response

Comment 1: In the main text, all the references are shown as [?].

Comment 4: The two sentences in lines 80 and 81 are a replication of the sentences above.

Comment 5: Line 101, p^- should be p̄ (p-bar)?

Response to Comments 1, 4, 5:
Thank you for pointing these out. The reference formatting issue has been corrected, the duplicated sentences have been removed, and the notation for the antiproton has been corrected to p̄.

Comment 2: The first sentence of the abstract ends with “atomic nuclear structures,” which is ambiguous. Do you mean atomic and nuclear structure?

Response 2:
Yes, we meant “atomic and nuclear structure.” This has been revised in the abstract for clarity.

Comment 3: In line 20, “negative particles” should be “anti-particles”?

Comment 6: Line 107, “single negative particle” should be specified. Does it mean antiproton?

Response to Comments 3 and 6:
Thank you for the suggestion. We have revised the phrasing for clarity: where the text refers specifically to antiprotons or antiparticles, we now use those terms explicitly. In other cases, we now use “negatively charged particles” where appropriate.