Multi-Reflection Time-of-Flight Mass Spectroscopy for Superheavy Nuclides
Round 1
Reviewer 1 Report
Summary:
The authors developed a multi-reflection time-of-flight mass spectrograph with an alpha-TOF detector to accurately measure the atomic masses for very low-yield superheavy nuclides. The authors summarized the previous studies, discussed the challenges and work to be done in the future.
Impact:
The authors presented a lot of details on the experimental setup and analysis methods. This manuscript is of clear interest to readers of Atoms, especially those working on nuclear physics and superheavy elements.
Issues:
1. In this manuscript, the authors didn’t really clarify what was the major challenge for measurement of superheavy nuclides compared to that of lighter ones. Is that the production of nuclides, resolution or something else? What is the major advantage of MRTOF-MS for measurement of superheavy nuclides compared to other approaches?
2. Is there a TOF mass spectrum for 257Db? It would be better to have that in the manuscript.
3. There are some grammatical errors and typos in texts, please fix them to improve the readability.
Author Response
We thank the reviewer for their critique. We will adjust the manuscript to better express that the extremely low production yield is the major difficulty in measuring the SHE, as it makes it difficult to distinguish between SHE ions and either background noise or some obscure stable contaminant -- we overcome this challenge by adding decay correlation to our detector so we can be certain our few detected ions are neither noise nor stable molecular ions.
We will add a time-of-flight spectrum for 257Db to the manuscript for reference. However, we are presently working on a separate manuscript dedicated to mass measurements the 25xDb isotopes, and so we do not want to include too many details of these results which might interfere with that publication.
We will attempt to correct the typos as best we can, although if we knew where they were we would have already corrected them. We implore the reviewer to offer specific examples of grammatical errors and typos, should any remain to be corrected in a second review round.
Reviewer 2 Report
In this manuscript, the authors describe the performance of an MRTOF-MS setup used at RIKEN's GARISII facility, which is capable of performing correlated mass and alpha decay measurements. The setup allows mass measurements to be made even on superheavy elements with extremely small production cross sections, providing valuable anchor points for nuclear models without relying on extrapolations based on alpha decay chains. In addition, the authors envisage the possibility of using the MRTOF method for A and Z identification of SHE radionuclides of the Dubna chain and possibly also for determining the order of isomeric nuclear states in the superheavy element range.
The very fact that high resolution and efficiency could be achieved to determine the mass of 257Db is fascinating to me. In this respect, every small step towards even heavier radionuclides is a milestone and deserves appropriate attention. However, this involves a lot of effort and I am aware that in the end one has only a few nuclear decays to evaluate in order to draw reasonable conclusions, if any.
I find this manuscript very well written and the results adequately presented. However, I also feel that some important aspects, which I list below, need to be addressed before possible publication
Major issues in the manuscript:
- In the introduction the authors mention nuclear deformation, but I wonder how the 2n separation energy can be a key probe for nuclear deformation unless many modelling assumptions have to be made before reaching such conclusions? Perhaps one wants to mean the changes in the deformation rather than the deformation itself. Could the authors clarify this issue?
- In many places in the manuscript (including the title) the term spectroscopy is used, which I recommend when a technique aims to study the energy spectra of elements or isotopes. Otherwise, spectrometry/spectrometer/spectrograph better describes the idea and setup. Also, I suggest replacing spectral peaks with TOF/mass peaks or something similar, because these are nothing more than such.
-line128: The authors state that the measurements in the concomitant reference method are essentially simultaneous. However, the fact that a real cycle of 5 minutes before and after the analyte measurements is considered in the data analysis later on seems contradictory. Could the authors clarify the contradictory statements in the text?
- line 283-286 + Fig.4: The data quality is rather poor, so any conclusion about the state assignments remains speculative, regardless of the PDF or Monte Carlo treatment. I suggest that the authors relax their statement or otherwise provide more experimental data to support their claim. Also, it is quite confusing when states are given with half-lives, especially when a half-life of 1.8s suddenly appears in the text without any prior reference to it.
- No discussion of the results/analysis is provided in Sec.4. I suggest the authors to name this section as, e.g., Summary and Outlook.
- An improvement of the resolving power of the spectrometer by more than a factor of 3 is mentioned in the manuscript which on the one hand arouses the interest of the reader to learn more about it and on the other hand is neither supported by data here nor justifies the single isolated sentence in line 298. Could the authors explain why they do not show a TOF peak in Fig.2, which would support their claim?
- Starting at line 317, the authors use first cautious and then confident language in describing MRTOF-MS prospects for SHEs, which is tantamount to extreme extrapolation. In my opinion, the manuscript provides no evidence to support the claim that MRTOF-MS provides very high confidence in identifying extremely low-yield SHEs or that current performance is sufficient to determine state order.
Minor corrections:
- SHE has to be introduced at its first appearance
- line 17: delete "are"
- line 24: add "about" after "informing"
-line 67: "is" instead of "are"
-line 68: remove "the combination"
-line 102: separated
-line108-110: Could the authors rephrase the sentence so that it is compatible with the consideration of energy losses in the polyimide window?
-line 115: remove "which"
-Fig.1: one should use the same names as given in the text such as "flat trap". Also there seems to be a central and a pulsed drift tube in the text which creates confusion to the reader if not indicated properly in the figure.
-line 125: what is the helium pressure for cooling? Generally, I am missing the indication of pressure requirements for the MRTOF-MS setup
-line 149: to be reflected
-line 176: delete "is"
-line 185: "sigma square" instead of "sigma"
-line 198-199: References are missing. What does "delta t" stand for?
-line 223: limiting
line228+229: "decay time(s)" instead of "lifetime(s)"
-line230: serves as a useful cross-check of radionuclide assignment
-Fig.3: use minor and major axis in the caption to describe the ovals instead of height and width. Also use "distributions" instead of "resolution". Indicate (in terms of keV) achieved fwhms.
-line256: not --> nor
-line270+271: lifetime --> half-life
-line275: the calculate --> calculate the
-line286: would --> to
-line301: spectral --> mass
-line314: "Due to in part" --> "Partly due" ; "in the" --> "the"
-line319: would --> to
-line323: in principle confirm
-line341-351: specify all mentioned isotopes in the last paragraph
-line376: Ref.4 is not given properly
Author Response
Please see attachement
Author Response File: 
Author Response.pdf
Reviewer 3 Report
The Authors presented an interesting setup (Multi-reflective time-of-flight mass spectroscopy) for superheavy nuclei. The improvement in the determination of the mass of new superheavy elements is crucial in nuclear chemistry for the accurate determination of the mass of new elements, but also for the determination of evaporation residue cross section, fundamental measurements for the experimental and theoretical investigations in heavy nuclear reactions.
The Authors well described the new setup and the analysis method, In my opinion, the Authors must better describe the evidence of the improvement of the new mass determination methods by comparing new measurements with old ones. The reader has the impression that the results of the use of the new detection method and analysis are only in progress.
If it is this the case, I suggest showing the results of the simulation and maybe some preliminary results, the Authors said "With these improvements a further, another measurement was recently made for 305 257,258Db with ∼20 decay-correlated time-of-flight events for each nuclide. The analysis is 306 ongoing"
Therefore, maybe some preliminary results are ready to be shown.
Readable but sometimes convoluted!
Author Response
We appreciate the reviewer's comments. We have made significant efforts to improve the readability by correcting several typos and what we presume must be autocorrect-induced word-choice-errors. If a second review round proves necessary, we would appreciate if the reviewer might point out specific errors in the language as it is incredibly difficult to self-correct these things.
We have extended the discussion of our simulations for state order determination in 257Db, adding an image array and including our code as supplemental materials. We also add a preliminary analysis of the latest data set for 257Db in comparison with our original data set, to demonstrate the improved performance of the MRTOF. We are still carefully evaluating this data and working on a separate manuscript to publish the results, probably not until after the final online run of this campaign in early 2024.
Reviewer 4 Report
The authors provide an interesting overview of the MRTOF-MS work on superheavy elements performed at RIKEN. The authors give a clear and sufficiently detailed overview of the experimental apparatus and its capabilities. Some new developments are discussed, and placed into the context of previously published measurements. An outlook to promising future measurement campaigns is given.
I have very few comments, which can be found below. They are all minor, so I see no issue in recommending this article be published in Atoms.
- Page 3, sentence which starts on line 114 - a word seems to be missing from the sentence.
- Page 6, line 223-225: By limiting ...
- Page 8 line 281: I believe 'reweight' should be 'reweigh', but could be mistaken - a native speaker like the first author may not agree...
-Page 8, Line 229: the system efficiency is quoted. It would be useful for the reader to know what this efficiency number includes transmission through GARIS, stopping, trapping, MRTOF, detection, or only a part of that chain? If there would be information on the efficiency of the individual stages, this may also be of interest.
Author Response
We thank the reviewer for their positive review and for providing detailed feedback of problems in the manuscript. We have attempted to improve the manuscript by correcting numerous typos and grammatical errors, while also extending the text to better explain the simulations that determine our level of confidence in state order assignment.
The issue at line 114 has been corrected. It seems two sentences in an early draft were poorly compressed to a single sentence.
The typo at line 223 has been corrected.
Regarding the issue at line 281, we have largely extended this section and hope the reviewer finds the new passages acceptable.
Regarding the system efficiency passage at line 299, we have modified it to read "The system efficiency for ions delivered by GARIS-II to reach the alpha-TOF detector after ~700 reflections in the MRTOF is now 5%--10%." Unfortunately, we do not have the diagnostics in place to evaluate the stopping or trapping efficiencies independently. We can not for the reviewer that there is minimal (maybe 10%) loss after 700 laps compared with ions passing through the MRTOF without being reflected.
Round 2
Reviewer 2 Report
The authors properly addressed the rised issues in the current version and provided additional and detailed results which support their conclusions.
I suggest publication in the present form.
Reviewer 3 Report
The Authors revised the manuscript addressing all remarks properly, therefore I recommend the paper for publication.
I suggest the authors use an English correction tool to improve the manuscript, there are available different.
