Talk:Direct measurements in Nuclear Astrophysics: ERNA and LUNA

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    This paper aims to give an introductory overview of the LUNA and ERNA nuclear astrophysics laboratories. It does a good job of describing the laboratories, although I have some comments and suggestions before I can approve it. Some of these comments address the readability of the article, and will help make it more accessible to readers unfamiliar with the topic.

    Section: Nuclear reactions in stars and on Earth

    1) I have a minor English grammar point that will help make the aritcle easier to read and more accessible to a wider audience. In general, most cases in the article that read ", that", should be replaced by ", which".

    2) "The famous physicist George Gamow first calculated the probability of penetrating the Coulomb barrier, that decreases exponentially for decreasing energy. In conclusion,..." "Conclusion" should be replaced by "summary"

    3) "named after Gamow as an acknowledgement of his contribution" is a strange addition to a scientific paper. It can be replaced by "the Gamow window".

    4) the assertion that "George Gamow first calculated the probability of penetrating the Coulomb barrier" requires a citation.

    5) Besides that discussion, saying that the Gamow Window is "where thermonuclear reactions occur in stars" is inaccurate. The concept of the Gamow window is only valid for non-resonance reaction cross-sections, although it is sometimes a useful tool for resonant reactions, thus frequently used for convenience. I refer the authors to an enlightening paper (Newton, J.R. et al., PRC 75, 045801 (2007)) regarding this. The discussion in the article should be clarified.

    6) "... detector efficiency allow to obtain..." should be changed to "... detector efficiency only allow us to obtain...".

    7) "But even in more favourable cases, the rate attainable in a laboratory is of the order of 1 d^-1 or less". Two points: (i) "attainable" should be replaced by "obtainable"; (ii) this assertion either needs a more detailed discussion, or should be removed. How do you define "favourable" cases, for example? Some astrophysically important resonance strengths can be measured at much higher rates than these. Especially for burning in novae etc. One example that comes to mind is the 193 keV resonance in 17O(p,g).

    8) "Unfortunately, this procedure does not work when...". This is a surprising statement. Especially the discussion of unexpected tails of resonances. I agree that the procedure of extrapolating high energy data is a poor procedure, but I believe this can be stated more eloquently. Resonance positions can be predicted through knowledge of the nuclear structure, for example. I believe that the main reason why these extrapolations are poor is that the uncertainties in models are large, and these uncertainties can be magnified through extrapolation. I suggest that this sentence is re-written.

    9) You cite the Rolfs "Cauldrons in the Cosmos" book, but this book is out-of-print. Since this article is aimed at a broad audience, I suggest that a more recent book is also included here. The Iliadis "Nuclear Physics of Stars" book is a good reference.

    10) A cross-section also varies smoothly. This sentence should be clarified.

    11) "extract relevant information" could be improved by specifying "extract relevant nuclear structure information".

    12) "more than compensated for...". The word "compensated" suggests that it's a positive thing, even though in this case, background created in shielding is bad. I would suggest "additional background from intereractions... overwhelms the positive effect of attenuation in the shielding...".

    13) A few sentences on: "Again, the attenuation if this background signal is made difficult by cosmic rays". This needs to be explained more clearly. How do cosmic rays make environmental background a problem?

    Section: The LUNA Experiment

    14) "built on a side" - "built at the side"

    15) The background attenuation values require citations.

    16) Same goes for background measured in the HPGe detector.

    17) "Indeed, as previously underlined" - "Indeed, as previously outlined"

    18) Your discussion of shielding "However, the shielding efficiency cannot be increased by further adding..." is a much better discussion of this effect than in the introduction. Maybe this sentence should be moved to the introduction.

    19) There is some repetition of discussion regarding the pp-chain when discussing the 3He(3He,2p) reaction.

    20) In your discussion of the 14N(p,g) reaction: "... allowed to reveal..." should be "allowed us to measure" or "enabled the measurement of"

    21) Similarly "allowed to determine" should be "allowed us to determine".

    22) "at the lowest energies" doesn't make much sense. "At low energies", or "at lower energies than any other experiment"...

    23) This discussion of 14N(p,g) would really be helped with a s-factor figure showing your data compared with others - including the results from LENA (see next point).

    24) There is no mention of the Runkle, R. et al., PRL 94, 082503 (2005) results! Why do you only cite papers from 1999 and 1987? Citations to the LUNA results should also be included.

    25) A citation is needed when discussing globular cluster age determination.

    26) You discuss 14N(p,g) in hydrogen shell burning. However, it is this rate in *core* hydrogen burning that effects the main sequence turn-off age (i.e., the time required for a star to exhaust it's hydrogen fuel in the core). See Kraus, L. et al., Science 299, (2003) 65-70

    27) At the end of this paragraph "of the same quantity" needs to be clarified.

    28) Next paragraph, you are missing a space after 3He(4He,g)7Be. Also missing is the word: "reaction" here.

    29) "the results obtained with the two techniques are in very good agreement" - needs to be shown.

    30) I do not understand the following "... were considered in the recent compilation to derive...". Does this mean that the LUNA results were considered to be the most reliable results? Or they were used along with those other results?

    31) Somewhere in this paragraph, I think you should explain what you mean by, for example, a 7Be neutrino. The intended audience is broad, so this could add valuable information.

    32) Next paragraph: "aboveground" should be two words. Previously you used the term "over-ground"... I personally prefer "above-ground" but it should be consistent throughout the article.

    33) "Texture of the isotopes". Texture refers to how something feels to the touch. This should be altered.

    34) Add a citation to the 12C+alpha "holy grail"

    35) "necessary services and implants" - I don't think "implant" is correct here.

    36) "A key issue is here" - "A key issue here is"

    37) "Montecarlo" should be "Monte Carlo" (two words, no hyphen)

    38) Figure 3 does not show any shielding, as promised in the text. Can the shielding be labelled?

    39) "The neutron flux is only 1% of LNGS natural background". What are the requirements before you are allowed to build?

    40) "has been studied by the ERNA collaboration in the past" needs a citation.

    Section: The ERNA Experiment

    41) The first few sentences are an introduction that are out of place here. These arguments should go in the article introduction. Here, the discussion should be more specific.

    42) To highlight the inverse kinematics nature of ERNA, could you use the conventional syntax for presenting reactions? For example: 4He(12C,16O)gamma?

    43) "equal to the one of the projectile" - "equal to that of the projectile".

    44) "the momentum of the recoils is varied" gives the reader the impression that the experimenter is varying the recoil momentum. A clearer replacement would be "the momentum of the recoils varies".

    45) In the paragraph discussing the principle of RMS, citations of examples would be helpful given the intended audience.

    46) I cannot read the axis title in the final frame of figure 4.

    47) "straightforward and generally acknowledged" should be replaced simply with "straightforward"

    48) "peculiar" should be "particular to" (peculiar means that it is strange).

    49) "RMS's" - "RMS facilities"?

    50) Citation needed for the NABONA collaboration if possible.

    51) "flow mode" and "recirculation" need to be explained.

    52) The Argon post-target stripping system needs some explanation. Why is it needed, etc?

    53) Figure 5: "AP" and "QS" don't seem to be defined.

    54) "The specification achieved set ERNA in the number of the world leading..." is a strange statement. Is it necessary? If so, can the level of background rejection be compared with other RMS facilities to back-up this claim?

    55) "than the selected one" - "than the selected ions"

    56) "implemented in occasion of" - This should be spelt out "implemented now that ERNA has been moved".

    57) It should be made clear earlier that ERNA has recently moved before discussion its previous and future operation

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