Triplet 12B-12C-12N : Search for States with Halo

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY 4.0 https://creativecommons.org/licenses/by/4.0/ Triplet 12B-12C-12N : Search for States with Halo ©2020 The Authors Published version Danilov, Andrey N.; Demyanova, Alla S.; Ogloblin, Alexey A.; Goncharov, Sergey A.; Belyaeva, Tatiana L.; Trzaska, Wladislaw H. Danilov, A. N., Demyanova, A. S., Ogloblin, A. A., Goncharov, S. A., Belyaeva, T. L., & Trzaska, W. H. (2020). Triplet 12B-12C-12N : Search for States with Halo. In NN2018 : Proceedings of 13th International Conference on Nucleus-Nucleus Collisions (Article 010031). Physical Society of Japan. JPS Conference Proceedings, 32. https://doi.org/10.7566/jpscp.32.010031 2020 Triplet 12B-12C-12N: Search for States with Halo Andrey N. DANILOV1*, Alla S. DEMYANOVA1, Alexey A. OGLOBLIN1, Sergey A. GONCHAROV2, Tatiana L. BELYAEVA3, and Wladislaw H. TRZASKA4 1National Research Centre “Kurchatov Institute”, Moscow 123182, Russia 2Lomonosov Moscow State University, GSP-1, Leninskie Gory, Moscow 119991, Russia 3Universidad Autónoma del Estado de México, C.P. 50000, Toluca, México 4Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland *E-mail: danilo[email protected] (Received July 20, 2019) Previously in [1] neutron halo was confirmed for the 2¯, 1.67 MeV and 1¯, 2.62 MeV states in 12B on base of Asymptotic Normalization Coefficients (ANC) method analysis of the obtained experimental data. An unexpected result was received for the unbound 3¯, 3.39 MeV state. Its halo radius was found to be increased and equal to ~ 5.9 fm. This result can be considered as an evidence of the halo-like structure in this 12B state. It should be noted that last neutron in this state has a non-zero orbital momentum (l=2). So question arises about possible existence of states with halo in other members of the isobaric triplet 12B - 12C - 12N. We can expect the formation of a proton halo in the 2¯, 1.19 MeV and 1¯, 1.80 MeV states of 12N and 2¯, 16.62 MeV and 1¯, 17.23 MeV states of 12C. To check this prediction preliminary Modified Diffraction Model (MDM) analysis of existing (3He,t) and (3He,3He’) experimental data was done. KEYWORDS: asymptotic normalization coefficients, neutron and proton halo; MDM model; radii of excited states 1. Introduction Recently the evidence of the excited states of light nuclei with nonstandard sizes and enlarged radii, located closely and above the particle-emission threshold, was convincingly demonstrated (see Ref. [2] and references therein). The existence of neutron halos in the short-lived excited states of some stable and radioactive nuclei was revealed, in particular, by the ANC analysis of the neutron-transfer reactions [3,4]. Thus Liu et al. [3] reported the observation of halos in the second (2¯, Ex = 1.67 MeV) and third (1¯, Ex = 2.62 MeV) excited states of 12B using the (d,p) reaction on 11B at Elab = 11.8 MeV by analyzing the data with the ANC method. Results of the our group ANC analysis of the 11B(d,p)12B reaction data at Elab = 21.5 MeV are shown in [1]. Radii of the valence neutron for the first 5 excited states of 12B were determined. In current work obtained results for excited states of 12B [1] are compared with preliminary results of MDM analysis of existing (3He,t) and (3He,3He’) literature data for isobar analog states in 12N and 12C. 2. Results and discussions 2.1 12B states JPS Conf. Proc. , 010031 (2020) ©2020 The Author(s) https://doi.org/10.7566/JPSCP.32.010031 32 must maintain attribution to the author(s) and the title of the article, journal citation, and DOI. Proc. 13th Int. Conf. on Nucleus-Nucleus Collisions 010031-1 This article is published by the Physical Society of Japan under the terms of the Creative Commons Attribution 4.0 License. Any further distribution of this work Proceedingsof13thInternationalConferenceonNucleus-NucleusCollisions Downloadedfromjournals.jps.jpby130.234.241.61on07/16/20 Calculations [1] showed that the rms radii of the last neutron in the second 2¯, 1.67 MeV and third 1¯, 2.62 MeV excited states of 12B far exceed those for the g.s. and the first 2+, 0.95 MeV excited state. Exactly, for the 2¯ state, the excess is a factor of 1.7, and for the 1¯ state, it is a factor of 2.1, with respect to the rms radius of the ground state. Summary on values of halo radii Rh and probabilities of the last neutron to be outside the range of the interaction radius D1 from ANC analysis of 21.5 MeV data [1] in comparison with results from [3] can be seen in Table 1. Table I. Results of our group ANC calculations [1] in comparison with results of [3]. Values of halo radius Rh and D1 are shown. State Rh (fm) [3] D1 (%)[3] Rh (fm) [1] D1 (%)[1] g.s. 3.16 ± 0.32 19.9 3.55 ± 0.20 11 1.67 4.01 ± 0.61 53.6 5.9 ± 0.3 53 2.62 5.64 ± 0.90 66.8 7.4 ± 0.4 62 3.39 5.9 ± 0.3 39 The large values of D1 coefficient, more than 50% (formal condition of halo), indicate that the last neutron spends more than 50% of its time outside the range of the core potential. In this case we can conclude that the rms radius of the last neutron wave function can be associated with the halo radius. From results of [1] condition D1 > 50% is strictly fulfilled for the 2¯, 1.67 MeV and 1¯, 2.62 MeV states. It confirms existence of halo for these states and a conclusion made in Ref. [3]. Nevertheless, analysis [1] indicated that the halo radii in these states are considerably large. The fifth 3¯, 3.39 MeV excited state is localized 0.02 MeV above the neutron-emission threshold. As this state belongs to the continuum spectrum, it made impossible a correct estimation of the ANC. In [1] the calculation was carried out with a very small positive neutron binding energy (ε = 0.1 MeV) and an estimation of the rms radius of the last neutron wave function was done. It was found to be Rh = 5.9 fm, which is a factor of 1.7 larger than that of the g.s. But D1 is less than 50%. Thus we propose that the 3¯, 3.39 MeV excited state in 12B is a neutron halo-like state with the orbital momentum l = 2 of the last neutron. 2.2 12N states To study isobar analog states of 12B in 12N we propose to use MDM [5,6]. To study 12N states, this method can be applied to the reaction (3He,t). Its first application made it possible to determine the proton halo in an unbound state of 13N [7]. We have studied existing literature data on 12C(3He,t)12N reaction [8,9]. This data is incomplete and there is no possibility to make definite answer on question about halo in 2¯ and 1¯ states of 12N. Literature data with excitation of the 2¯ and 1¯ states is present only for 2 energies: 49.8 [8] and 81 MeV [9]. 49.8 MeV data contains angular distribution only for the 2¯, 1.20 MeV state. 81 MeV data contains all needed states interested for us (2¯, 1.20 MeV and 1¯, 1.80 MeV) but the problem is that only one oscillation in angular distributions is present. We applied MDM [5,6] to existing experimental data on 12C(3He,t)12N at E(3He) = 49.8 and 81 MeV [8,9]. Preliminary results of analysis are present in Table 2 with 010031-2JPS Conf. Proc. , 010031 (2020)32 Proceedingsof13thInternationalConferenceonNucleus-NucleusCollisions Downloadedfromjournals.jps.jpby130.234.241.61on07/16/20 comparison to data obtained for 12B [1]. Note that the rms matter radii (Rrms) of 12B and 12N in the ground states are adopted as 2.39 and 2.47 fm, respectively [10]. Table II. Preliminary results of MDM analysis on 12C(3He,t)12N experimental data [8,9] in comparison to results obtained for 12B from Ref. [1]. Values of root mean square radii are present. State 12B Rrms (fm) [1] 12N Rrms (fm) 1+ g.s. 2.39 ± 0.02 g.s. 2.47 ± 0.07 2¯ 1.67 2.58 ± 0.11 1.19 2.7 ± 0.3 1¯ 2.62 2.86 ± 0.11 1.8 2.8 ± 0.2 As can be seen from Table 2, close radii were obtained for isobar analog states in 12B and 12N by 2 independent methods: MDM and ANC. This preliminary result can be an argument for possible proton halo in 2¯ and 1¯ states in 12N. But further analysis is needed. It should be mentioned that new experiment on 12C(3He,t)12N reaction at E(3He)=40 MeV was done by our team at the end of 2018, now analysis is in progress. 2.3 12C states We found only one work with experimental data on inelastic scattering with excitation of the 2¯, 16.62 MeV state in 12C: 12C(3He,3He’)12C at E(3He)=49.8 MeV [8]. Preliminary MDM analysis of this data gave increased radius Rrms > 3 fm for 2¯ state. 3. Conclusion Previously in [1] neutron halo was confirmed for 2¯ and 1¯ states in 12B and probable halo-like structure was seen for 3¯ state of 12B (unbound, l=2). In this work MDM was applied to existing literature 12C(3He,t)12N and 12C(3He,3He’)12C data with the excitation of isobar analog states 2¯ and 1¯ in 12N and 12C. Preliminary results of MDM analysis for 12N states showed that rms radii are close to corresponding values of rms radii obtained by ANC for 12B. This fact can be an argument for possible proton halo in 2¯ and 1¯ states in 12N. MDM analysis also showed increased radius for the 2¯, 16.62 MeV state in 12C. Acknowledgment The work was supported by the Russian grant RSF 18-12-00312. References [1] T.L. Belyaeva et al., Phys. Rev. C 98, 034602 (2018). [2] A.A. Ogloblin et al., Nuclear Particle Correlations and Cluster Physics, pp. 311-338 (2017). [3] Z. Liu et al., Phys. Rev. C 64, 034312 (2001). [4] T.L. Belyaeva et al., Phys. Rev. C 90, 064610 (2014). [5] A.N. Danilov et al., Phys. Rev. C 80, 054603 (2009). [6] A.S. Demyanova et al., Yad. Fiz. 80, 427 (2017) [Phys. At. Nucl. 80, 831 (2017)]. [7] A.S. Demyanova et al., JETP Letters 104, 526 (2016). [8] G. Ball and J. Cerny, Phys. Rev. 177, 1466 (1969). [9] W. Sterrenburg et al., Nucl. Phys. A 405, 109 (1983). [10] A. Ozawa, T. Suzuki, and I. Tanihata, Nucl. Phys. A 693, 32 (2001). 010031-3JPS Conf. Proc. , 010031 (2020)32 Proceedingsof13thInternationalConferenceonNucleus-NucleusCollisions Downloadedfromjournals.jps.jpby130.234.241.61on07/16/20