The New Physics in LILITA_N21: An Improved Description of the Reaction 190 MeV ⁴⁰Ar + ²⁷Al

Round 1

Reviewer 1 Report

The manuscript “The new physics in LILITA_N21: an improved description of the reaction 190 MeV 40Ar +27 Al” presents an analysis of light charged particle emission in the evaporation residue channel for the 190 MeV 1 40Ar + 27Al reaction using the recently updated version of the Monte Carlo fusion–evaporation code LILTA_N21. 

The authors compare available experimental data to their calculations, using a spherical shape and nuclear stratosphere model within LILTA_N21, furthermore to previous calculations performed by the GANES code based on the standard statistical model. Hereby, a clear improvement and reasonable reproduction of data are observed. 

The paper is well and clearly written and presents a timely analysis using new available code. I believe the presented analysis to be highly suitable for publication in Applied Sciences. I have one comment, however, that should be addressed before publication. 

The PhD thesis of one of the authors is available online where a similar analysis has been performed using LILITA_N18 (http://www.fedoa.unina.it/12723/1/Thesis_PhD_Davide.pdf, section 3.1), already showing good agreement with the experimental data. It would be interesting to understand what the further improvement of version N21 constitutes. What new physics has been implemented compared to the N18 version and how does it improve the data?

And one minor issue, the “2” in the y-axis label of figure 1 should be a superscript. 

Author Response

Q1) The PhD thesis of one of the authors is available online where a similar analysis has been performed using LILITA_N18 (http://www.fedoa.unina.it/12723/1/Thesis_PhD_Davide.pdf, section 3.1), already showing good agreement with the experimental data. It would be interesting to understand what the further improvement of version N21 constitutes. What new physics has been implemented compared to the N18 version and how does it improve the data?

A1) The original version of the code has been modified by our group several times in the last decade. Some most recent modifications, concerning the spectra fit to optimize the Nuclear Stratosphere model parameters and the parallelization of the code, are part of the thesis mentioned by the referee (LILITA_N18). After the completion of his PhD by Davide, we've performed a complete rewriting of the code (LILITa_N21), adding several new model options (described in Davide, F.; Di Nitto, A.; Vardaci, E.; La Rana, G. Nucl. Instrum. Meth. Phys. Res. A 2022, 1025, 166178. doi:10.1016/j.nima.2021.166178) which will be essential for our project aimed at studying the decay of light system with high spin. The new code contains a series of small modifications, including:  i) the update of the masses of the main ejectiles (n,p and alpha); ii) the extension of mass and spin intervals of the matrices used to calculate the nuclear potential; iii) an increase of the maximum angular momentum of light charged particles.

Q2) And one minor issue, the “2” in the y-axis label of figure 1 should be a superscript.

A2) Thank you very much, the text has been modified according with your suggestion; we will submit the new version soon. 

Reviewer 2 Report

The work presents a study performed by using a Monte Carlo approach to compound nucleus decay after a nucleus-nucleus reaction. The technique is well known and provides significant results, but has some problems that should be avoided as much as possible: the number of parameters can be very large; the excess of parameters can mascarade important physical aspects of the problem.

To avoid those traps, one must adopt a method of reducing the number of parameters by the inclusion of physical processes details, providing a more realistic description of the nuclear reaction. This can be achieved only by providing a full description of the nuclear reaction, including the entrance processes, the time evolution of the reaction, the thermalization and the decay processes after the prompt emission of nucleons and small clusters. Then, each of the physical processes must be checked and adjusted to describe a whole lot of data, in systematic analyses observing different aspects of the reaction for different reaction energies and induced by different particles.

The work presented here features none of the characteristics described above. Just a few data is used to fit a model that describes only a part of the process by fitting too many parameters.  In this way, there is not any guarantee that the values obtained through the fitting have any physical relevance.

This work cannot be accepted for publication in its present form.

Author Response

Thanks for your comments. The approach you've suggested is of course appealing, but different from the statistical model of compound nucleus reaction, that has been improved with the inclusion of multi-step Monte-Carlo and the introduction of a nuclear stratosphere. This is clearly not the most general approach to nuclear reactions, but has shown to correctly reproduce several aspects of the above-mentioned processes.  

Reviewer 3 Report

In this paper authors investigated the particle emission in the evaporation residue channel for the 190 MeV, 40Ar +27 Al reaction, leading to 67Ga composite nuclei at Ex=91 MeV and angular momentum up to 46. They traied to show effectiveness of their multistep Monte Carlo approach in LILITA_N21.

The subject is interesting and is of importance for both theoretical and experimental physicists and the results seem to be trust able based on the previous publications of some of the authors in this field of research. But in order to make the paper more useful I can add some comments on it:

1- In my opinion since Applied Sciences is a general science journal and not a nuclear physics one, adding  a short section on the theory of SM and multistep Monte Carlo approach to this theory will make the paper more beneficial. I am aware of the explanations about these topics in the text but I am talking a separate section with "mathematical formulas".

2- The comparison that was used in this paper is done with the results of spherical case that was presented in Ref[1]. As it is mentioned in the reference  the comparison between the spherical and deformed case has been don with the old code. In order to show the effect of  changes that were taken into account in in the new code and their impact on the results it seems more appropriate, at least to me, to compared the new code's results with the deformed results of the reference.

3- It would be nice if the authors could talk a little more about the low energy region of their tesults.

Author Response

Q1)- In my opinion since Applied Sciences is a general science journal and not a nuclear physics one, adding  a short section on the theory of SM and multistep Monte Carlo approach to this theory will make the paper more beneficial. I am aware of the explanations about these topics in the text but I am talking a separate section with "mathematical formulas".

A1) We wrote a first draft of an appendix containing some of the formulas that could be relevant for an introduction to the statistical model; however, in our opinion, this additional section would end up either containing just few mathematical relations, not really enhancing the reader comprehension of the matter, or being longer than the article itself. In brief, we do think that it could be better to suggest a good review article to the interested reader (as, for instance, the works by Erich Vogt, "The statistical theory of nuclear reactions" - Advances in nuclear physics, 1968: 261-342 and by A.J. Cole, "Statistical Model for Nuclear Decay", Institute of Physics Publishing Bristol and Philadelphia 2000: 1-201).

 

Q2) The comparison that was used in this paper is done with the results of spherical case that was presented in Ref[1]. As it is mentioned in the reference the comparison between the spherical and deformed case has been done with the old code. In order to show the effect of changes that were taken into account in the new code and their impact on the results it seems more appropriate, at least to me, to compare the new code's results with the deformed results of the reference.

A2) Thank you very much for your comment. We discussed about the possibility of introducing the comparison you have suggested, but we concluded that it would not be as meaningful as it could appear at a first sight. The point is the following: in ref. [1] a so-called hyperdeformation was considered for all the angular momentum, whereas in our calculations the expected deformation is small. Although the spectra are reproduced through the Nuclear Stratosphere (NS) model parameters, which implicitly account for the deformation of the system, only small differences appear by comparing these calculations with those without the NS. Stratosphere effect is more important for nuclei with larger masses, but for the sake of completeness we have considered it also for the light system discussed in the paper. The improvement in reproducing the experimental data that we have observed with respect to GANES, should be attributed mainly to: (i) the use of a multi-step code; (ii) the new Optical Model Transmission coefficients;(iii) the large amount of computational time available, allowing to perform a detailed scanning, with calculations based on a wide statistic.

Q3) It would be nice if the authors could talk a little more about the low energy region of their results.

A3)Thank you.

The Original text:

“In Fig. 1 we show the proton and α -particle energy spectra from the evaporation channel. All the spectra are normalized to the maximum to evidence the differences. The experimental data and the GANES simulation results are taken from [1]. By adopting the global transmission coefficients OM described above and the multi-step LILITA_N21 code, both NS and SS calculations show large improvements with respect to those obtained by with the single-step code GANES in which emitting nuclei with spherical shapes have been assumed. LILITA_N21 well reproduces both low- and high-energy sides of the spectra. The LILITA_N21 well reproduces both low- and high-energy sides of the spectra.”

has been modified as:

“The energy and angular distributions and the abundance of evaporative LCP emission can give important information concerning the statistical properties of hot, rapidly rotating nuclei. In particular, the shape of the low-energy cutoff of an evaporative spectrum is controlled by the effective barrier (or its time-reversed capture process). Consequently, we can expect the spectra and angular distributions to reflect the role of effective emission barriers, which are associated to the shapes of the emitters.

In the attempt to refine the description of the relevant potential barrier between cold nuclei, the fusion data available in 80s’ paved the way to the development of transmission coefficients from fusion systematics in replacement of the existing ones extracted, since the 70s’, by considering only elastic scattering data. The authors of (L. C. Vaz and J. M. Alexander Z. Phys. A - Atoms and Nuclei 318, 231-237 (1984)), indeed, recognize that the fusion cross sections (the inverse process of evaporation) are more relevant than the elastic scattering cross sections to anchor the evaporation calculations. Transmission coefficients built by considering only fusion cross sections were later implemented in the GANES code and used to analyze the reaction under study [1]. In the work by L. C. Vaz and J. M. Alexander only fusion barriers of light charged particles were considered, while it is known that a strong competition between protons and neutrons emission exists. Probably this is one of the reasons that could explain why GANES code does not reproduce the proton spectra even by assuming a large deformation [1].

On the basis of this considerations, we implemented in our code the global OM parameters taken from (A.J. Koning and J.P. Delaroche Nuclear Physics A 713 (2003) 231). The potential parameters, indeed, have been derived by considering: (i) data set including different observables from both non-elastic and elastic scattering data; (ii) a reliable competition between the neutron and proton emissions assured by the use of the same functional form for protons and neutrons except for the Coulomb correction term.

However, it is worth to mention that OM parameters are extracted by fitting experimental data collected using target nuclei in their ground states, thus the deformations of the compound nuclei, such as those predicted by the RLDM, can modify the evaporation barrier. To extend the validity of our approach in a broad mass region we introduced the possibility to modulate our transmission coefficients calculated using the Optical Model potential by means of the Nuclear Stratosphere parameters.

In Fig. 1 we show the proton and α -particle energy spectra from the evaporation channel. All the spectra are normalized to the maximum to evidence the differences. The experimental data and the GANES simulation results are taken from [1].

We can see in Fig. 1 as LILITA_N21 calculations well reproduces both low- and high-energy sides of the spectra.”

Round 2

Reviewer 2 Report

The present version does not improve in any of the aspects mentioned in the first review. My opinion is that the manuscript does not suit the journal standards and must be rejected.