We report some recent experimental results on the spectroscopy of 13C and 20Ne nuclei by means of low energy nuclear reactions carried out with high resolution electrostatic accelerators. In the case of 13C we investigated the possible existence of a-cluster states above the a emission threshold by means of low energy elastic resonant scattering α+9Be in direct kinematics. Excitation functions show the presence of various resonances that have been reproduced by R-matrix fit. We studied also the structure of 20Ne by means of the 19F(p,α0) reaction at sub-barrier energies. The spectroscopy of 20Ne excited states in the region Ex 13.5-14.0 MeV can be probed by analyzing experimental angular distributions and excitation functions. This reaction plays an important role also in the CNOF cycle and is an important ingredient to describe hydrogen-induced destruction of fluorine in massive stars. For this reason we investigated the trend of S-factor, that has been compared with results previously reported in the literature. © Published under licence by IOP Publishing Lt

Campajola, L.

Dell'Aquila, D.

La Commara, M.

Lombardo, I.

Ordine, A.

Rosato, E.

Spadaccini, G.

Vigilante, M.

Journal of Physics : Conference Series

Archivio della ricerca - Università degli studi di Napoli Federico II

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Please scroll down to see the full text.Download details:IP Address: 192.84.134.230This content was downloaded on 21/11/2016 at 11:11Please note that terms and conditions apply.You may also be interested in:The influence of inelastic neutrino interactions with light clusters on core-collapse supernovasimulationsShun Furusawa, Hiroki Nagakura, Kohsuke Sumiyoshi et al.Equation of state for nuclear matter in core-collapse supernovae by the variational methodH Togashi, Y Takehara, S Yamamuro et al.Molecular dynamics simulation of nanoindentation of nickel-titanium crystalG B Sushko, A V Verkhovtsev, A V Yakubovich et al.Cointegration and Nonstationarity in the Context of Multiresolution AnalysisK Worden, E J Cross and A KyprianouDAMA/LIBRA results and perspectivesR Bernabei, P Belli, F Cappella et al.Clustering structure of nuclei in deep inelastic processesM Hirai, S Kumano, K Saito et al.Fragmentation in nuclear reaction and its relation to EOSAkira OnoStudy of Nuclear Structure of 13C and 20Ne by Low Energy Nuclear ReactionsView the table of contents for this issue, or go to the journal homepage for more2014 J. Phys.: Conf. Ser. 569 012068(http://iopscience.iop.org/1742-6596/569/1/012068)Home Search Collections Journals About Contact us My IOPscienceStudy of Nuclear Structure of 13C and 20Ne by LowEnergy Nuclear ReactionsI Lombardo1;2, L Campajola1;2, D Dell'Aquila3;4, M La Commara1;2,A Ordine2, E Rosato1;2, G Spadaccini1;2 and M Vigilante1;21 Dipartimento di Fisica, Universita di Napoli Federico II, Via Cinthia, 80126, Napoli, Italy2 Istituto Nazionale di Fisica Nucleare - Sezione di Napoli, Via Cinthia, 80126, Napoli, Italy3 Dipartimento di Fisica ed Astronomia, Universita di Catania, Via S. Soa, 95125, Catania,Italy4 Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, Via S. Soa, 95125,Catania, ItalyE-mail: ivlombardo@na.infn.itAbstract. We report some recent experimental results on the spectroscopy of 13C and 20Nenuclei by means of low energy nuclear reactions carried out with high resolution electrostaticaccelerators. In the case of 13C we investigated the possible existence of -cluster statesabove the  emission threshold by means of low energy elastic resonant scattering +9Be indirect kinematics. Excitation functions show the presence of various resonances that have beenreproduced by R-matrix t. We studied also the structure of 20Ne by means of the 19F(p,0)reaction at sub-barrier energies. The spectroscopy of 20Ne excited states in the region Ex 13.5-14.0 MeV can be probed by analyzing experimental angular distributions and excitationfunctions. This reaction plays an important role also in the CNOF cycle and is an importantingredient to describe hydrogen-induced destruction of uorine in massive stars. For this reasonwe investigated the trend of S-factor, that has been compared with results previously reportedin the literature.1. IntroductionLow Energy Nuclear Reactions between light ions are an important tool for carefully probing thestructure of light nuclei [1]. In particular, it is possible to deduce information about the possibleexistence of -cluster states in light nuclei, a subject of large interest in Nuclear Physics [1, 2]. Tothis aim, dierent type of nuclear reactions can be used. For example, direct reactions as (6Li,d)and (7Li,t) at some tens of MeV, leading to -transfer processes on the target nucleus, havebeen often used to probe the existence of -structures in light nuclei [3, 4]. Other experimentalways to probe the -structure of light nuclei are the study of resonant elastic scattering (indirect or inverse kinematic) of 4He nuclei on various targets [5, 6, 7] or, in general, the studyof nuclear reactions leading to the formation of a given compound nucleus that subsequentlyde-excites by emitting -particles. In the rst part of this paper we describe some investigationson the structure of the 13C nucleus via the resonant elastic scattering of  particles on 9Be indirect kinematics [8, 9]. In this way it is possible to explore an excitation energy region in 13Cwhere the existence of rotational bands built on molecular states has been suggested [10]. Inthe second part of the paper we discuss on the spectroscopy of 20Ne excited states by means3rd International Workshop on “State of the Art in Nuclear Cluster Physics” IOP PublishingJournal of Physics: Conference Series 569 (2014) 012068 doi:10.1088/1742-6596/569/1/012068Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd 10100200300400500600700800500 1000 1500 2000 2500 3000 3500 400011010 210 31000 2000Figure 1. (Left panel) Experimental spectra of +9Be scattering at 150 and 70 (insert), at6.06 and 9.48 MeV bombarding energies. (Right panel) Elastic scattering excitation functionobtained at cm=168.7 (open circles) and preliminary R-matrix t to the experimental data(red line).of the 19F(p,0) reaction at sub-Coulomb energies [11]. In this case the analysis of excitationfunctions and angular distributions allows to rene the spectroscopy of 20Ne in the excitationenergy range Ex  13.5-14.0 MeV, where uncertain J assignment are still persisting in theliterature. Furthermore we extracted the S-factor in the energy region Ecm ' 0.57-1.0 MeV,where two dierent trends are reported in the literature. Our work allows to shed light on thisdiscrepancy and points out the need for further measurements at lower energies. Good qualitydata at low energies are important because this reaction is involved in the CNOF cycle during thehydrogen-burning phase in stars [12] and represents an important channel of uorine destructionin hydrogen-rich stellar environments [13, 14]. Both the experiments have been carried out atthe TTT-3 tandem in Naples [15] and will be briey described in the following paragraphs.2. Structure of 13C via +9Be elastic scatteringBetween the various non-self-conjugated nuclei, the study of 13C excited states above the emission threshold probably constitutes one of the most interesting physical cases. In fact, thestructure of some excited states could be described in term of an excitation of the Hoyle statein a 12C core coupled with a covalent neutron [16]. Information on the structure (included theradius and the moment of inertia) of these states could be useful to shed light on the structure ofthe 12C nucleus. In this framework the possible presence of molecular-like states in highly-lyingexcited states of 13C has been suggested in [10] starting from the available data reported inthe literature [17]. This and other theoretical works stimulated experimentalists to rene thespectroscopy of 13C near and above the  threshold.A powerful way to perform these investigations is represented by the analysis of resonancesin +9Be elastic scattering excitation functions at backward angles. Unfortunately, very fewexperimental data have been reported in the literature. An old paper by Goss et al [5] reportedon the elastic scattering in direct kinematics in a broad angular range (50-160) but in a limitedbombarding energy domain (Elab 2.0-5.0 MeV), while in a more recent paper Freer et al[6] reported an excitation function obtained with the inverse kinematic thick target method3rd International Workshop on “State of the Art in Nuclear Cluster Physics” IOP PublishingJournal of Physics: Conference Series 569 (2014) 012068 doi:10.1088/1742-6596/569/1/0120682at around 180 in the energy domain Ecm 2.0-7.0 MeV. In both cases, information on theJ of various states have been deduced by R-matrix t of experimental data. Anyway, someuncertainties on J assignments are still persisting, thus stimulating a new experiment coveringa broader energy and angular domain. We performed this experiment in direct kinematics atthe TTT-3 tandem accelerator in Naples [15]; details on this experiment can be found in [8, 9].We checked the absolute scale of experimental cross sections by performing both thin and thicktarget experiments [8]. An example of spectra obtained at backward angles is reported in the leftpanel of Figure 1. The presence of elastically and inelastically scattered  particles from 9Be andcontaminants constituting the target is recognized by kinematics and energy loss considerations.An example of excitation function of the +9Be elastic scattering at cm=168.7 is reported inthe right panel of Figure 1 (open circles). The red solid line indicates the result of a preliminaryR-matrix t to the experimental data, obtained by using the minRmatrix code [18, 19]. Theeect of target thickness has been taken into account in performing the t procedure. Theseresults are still preliminary and will be extended in the future to other excitation functionsobtained at dierent angles. Nevertheless, we can extract some interesting information fromthis preliminary analysis. First of all, in the energy domain here explored, it seems that no 1=2states are excited, in agreement with data by [6]. Therefore the excitation energy of a possiblestate obtained by coupling in s-wave a neutron with a 12C core excited to the Hoyle state shouldbe lower than the minimal excitation energy probed in this experiment, and this is in agreementwith recent amd calculations [16]. Another interesting point concerns the resonant structure atEcm 3.5 MeV. Our preliminary results pointed out the presence of two close-lying states withJ=5/2 ,7/2+ with quite low values of dimensionless reduced widths for the 0 channel (of theorder of some percent of the Wigner limit). These preliminary results are in good agreementwith the ndings of [5] and seems to rule out the presence of a 9/2  state at this excitationenergy, needed to support the existence of the molecular negative-parity rotational band in 13C.Further investigations on the present experimental data are currently going on.3. Investigation of the 19F(p,0) reaction at low energiesThe investigation of low energy 19F(p,0) and19F(p,) reactions has been used in the pastto probe the structure of 20Ne, which is a self-conjugated nucleus and can show pronounced -cluster structures [20]. To this aim experimental eorts have been performed [21, 22] to evidencethe existence of quartet excitations in this nucleus [23, 24]. Unfortunately, ambiguities in thespectroscopy of some excited states are still persisting, especially in the excitation energy regionaround 13.3-14.0 MeV [25]. Beyond the spectroscopic motivation, the 19F(p,) reaction playsa signicative role in Nuclear Astrophysics because it closes the CNOF cycle in the hydrogen-burning phase of massive stars [12] and can represent an important channel of uorine destructionin hydrogen-rich stellar environments [13, 14]. Despite of this interest, very few (and oftencontrasting) data-sets of the S-factor at Ecm < 1 MeV have been reported in the literature, thuspreventing an accurate reaction rate determination at astrophysical energies [26]. Taking intoaccount both these aspects, we performed a new experiment at the TTT-3 tandem acceleratorin Naples, aimed at measuring angular distributions and excitation functions of the 19F(p,0)reaction in the bombarding energy domain Ep 0.6-1.0 MeV. The details of this experiment arewidely discussed in [11]. In the following sections we report some experimental ndings relatedto this experiment.An array of 12 silicon detectors covering a large angular range has been used as detectionsystem. Thin aluminium foils preceded silicon detectors in order to stop the high ux ofscattered particles; at variance, they allow the passing through of high energy -particles emittedin the 19F(p,0) reaction (Q=8.114 MeV). The obtained experimental spectra are practicallybackground-free. Due to the low bombarding energy domain (Ep 0.6-1 MeV), only s, p and dpartial waves are expected to mainly contribute; for this reason, angular distributions have been3rd International Workshop on “State of the Art in Nuclear Cluster Physics” IOP PublishingJournal of Physics: Conference Series 569 (2014) 012068 doi:10.1088/1742-6596/569/1/01206835101520253035400.5 0.6 0.7 0.8 0.9 1Figure 2. (Left panel) Best ts of 19F(p,0) experimental angular distributions in terms ofLegendre polynomials, as a function of the bombarding energy. (Right panel) 19F(p,0) S-factor extracted in the present experiment [11] and compared with literature data [21, 27, 28]as reported in nacre [26].tted with Legendre polynomials up to 4th degree [21, 27, 28]. The distributions of coecientsof the polynomial expansions around resonance energies allow to estimate the relative orbitalangular momentum in the outgoing channel and therefore the J of excited states [21, 27, 28].The evolution of angular distributions as a function of bombarding energy is displayed in Figure2 (left panel). A continuous shape evolution is evident, pointing out the excitation of variousstates with dierent J. The analysis of angular distributions has been largely discussed inRef. [11]; in this way we obtained J assignment of various states for which contrasting valueswere reported in the literature [25]. For example, the Ep=842 keV (E=13.642 MeV) state hasbeen ambiguously reported to be 0+ [21, 29] or alternatively 2+ [28]. From the analysis of thepresent data in the Ep=810-860 keV interval we deduce a 0+ assignment for the 842 keV state.Moreover, a contribution from a 1  state at Ep  825 keV partially merged into the previousone has been seen [11]. Further details on this analysis can be found in Ref. [11].As discussed at the beginning of this paragraph, the 19F(p,) reaction plays an importantrole also in Nuclear Astrophysics, with the 19F(p,0) channel being dominant at T < 0.1 GK[30]. The recommended values of the 19F(p,0) S-factor at low energies are reported in nacre[26]. They are taken from Breuer (Ecm=461-684 keV [27]), Isoya et al (Ecm=598-1385 keV [28]),Caracciolo et al (Ecm=760-817 keV [21]) and Cuzzocrea et al (Ecm=1476-2544 keV, [22]). Inmore recent times, indirect data obtained with the Trojan Horse Method pointed out the roleplayed by the low-energy resonance at Ecm =113 keV [14].We can recognize two dierent behaviors of experimental data at Ecm < 0.7 MeV, where thedata of Refs. [27] and [28] dier by a factor of  40%. This discrepancy aects the non-resonantextrapolation made in [26], and therefore the reaction rate determination at stellar energies. Inthe experiment here discussed, we extracted the S-factor from the experimental dierential crosssections in the range Ecm=577-982 keV [11]. The results are shown in the right panel of Figure 2together with data reported in nacre [26]. A reasonable agreement (within the errors) betweenpresent results and Refs. [21, 28] is seen in the energy region Ecm 800 keV. Furthermore,the S-factor smoothly increases with decreasing energy at Ecm < 650 keV, in good agreementwith results by [27]. This behavior could be attributed to the excitation of two broad states(0+; 1 ) at E =13.224 MeV [27]. Moreover, our data and Breuer ones [27] in the Ecm  550-650keV interval are about 40% larger than the Isoya et al ones [28]; consequently, extrapolationsmainly based on this data set can underestimate the low energy non-resonant S-factor values.These ndings stimulate to explore the low energy region of the 19F(p,0) S-factor with newdirect investigations. To this aim, a new experiment has been recently performed at Laboratori3rd International Workshop on “State of the Art in Nuclear Cluster Physics” IOP PublishingJournal of Physics: Conference Series 569 (2014) 012068 doi:10.1088/1742-6596/569/1/0120684Nazionali di Legnaro, exploring the 19F(p,0) S-factor down to Ecm = 180 keV. Data analysisis currently going on.4. ConclusionsIn this paper we reported some recent results about the structure of 13C and 20Ne nuclei,investigated by means of resonant elastic scattering (+9Be) and low energy nuclear reactions(19F(p,0)) respectively. On the side of13C structure, the appearance of anomalies in thedierential cross sections is associated to the excitation of various states in 13C above the threshold. R-matrix analysis of experimental data is currently in progress. Concerning the19F(p,0) reaction, from the analysis of angular distributions we estimated the J of variousexcited states of the compound nucleus 20Ne, trying to solve some ambiguities still persistingin the literature. The trend of the S-factor has been also explored down to Ecm 0.55 MeVand has been compared with results reported in the literature, pointing out the need to increasethe non-resonant contribution with respect to the currently adopted extrapolations. In thisframework a new experiment, aimed at exploring the S-factor down to Ecm 0.18 MeV, hasbeen recently performed and the analysis is currently ongoing.We are strongly indebted to Prof. G. Rogachev for the use of minRmatrix code. Weacknowledge also Prof. E. Perillo for useful discussions.References[1] von Oertzen W, Freer M and Kanada En'yo Y 2006, Phys. Rep. 432 43[2] von Oertzen W 1996, Zeit. Phys. A 354 37[3] Rodrigues MRD et al 2014, Phys. Rev. C 89 024306, and this conference proceedings.[4] Wheldon C et al 2012, Phys. Rev. C 86 044328[5] Goss JD et al 1973, Phys. Rev. C 7 1837[6] Freer M et al 2011, Phys. Rev. C 84 034317[7] Zadro M et al 2007, Nucl. Instrum. Methods B 259 836[8] Lombardo I et al 2013, Nucl. Instrum. Methods B 302 19[9] Lombardo I et al 2013, J. Phys. Conf. Ser. 436 012021[10] Milin M and von Oertzen W 2002, Eur. Phys. Jour. A 14 295[11] Lombardo I et al 2013, J. Phys. G: Nucl. Phys. 40 125102[12] Rolfs C and Rodney WS 1988, Cauldrons in the Cosmos, Chicago Univ. Press[13] Lucatello S et al 2011, Astr. Jour. 729 40[14] La Cognata M et al 2011, Astr. Jour. Lett. 739 L54[15] Campajola L et al 1987, Nucl. Instrum. Methods B 29 129[16] Chiba Y and Kimura M 2014, this conference proceedings.[17] Ajzenberg-Selove F 1991, Nucl. Phys. A 523 1[18] Rogachev G et al 2014, this conference proceedings.[19] Rogachev G et al 2007, Phys. Rev. C 75 014603[20] Beck C (ed.) 2010, Lect. Not. Phys. 818, Vol. 1[21] Caracciolo R et al 1974, Lett. Nuovo Cim. 11 33[22] Cuzzocrea P et al 1980, Lett. Nuovo Cim. 28 515[23] Arima A, Gillet V and Ginocchio J 1970, Phys. Rev. Lett. 25 1043[24] Middleton R, Garret JD and Fortune HT 1971, Phys. Rev. Lett. 27 950[25] Tilley DR et al 1998, Nucl. Phys. 636 249[26] Angulo C et al 1999, Nucl. Phys. 656 3[27] Breuer G 1959, Zeit. Phys. 154 339[28] Isoya A, Ohmura H and Momota T 1958, Nucl. Phys. 7 116[29] Webb T S, Hagedorn F B, Fowler W A and Lauritsen C C 1955, Phys. Rev. 99 138[30] Spyrou K et al 2000, Eur. Phys. Jour. 7 793rd International Workshop on “State of the Art in Nuclear Cluster Physics” IOP PublishingJournal of Physics: Conference Series 569 (2014) 012068 doi:10.1088/1742-6596/569/1/0120685

Study of nuclear structure of 13C and 20Ne by low energy nuclear reactions

I Lombardo

L Campajola

D Dell'Aquila

M La Commara

A Ordine

E Rosato

G Spadaccini

M Vigilante

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Journal of Physics Conference Series

Study of Nuclear Structure of<sup>13</sup>C and<sup>20</sup>Ne by Low Energy Nuclear Reactions

https://www.iris.unina.it/retrieve/handle/11588/614946/294562/jpconf14_569_012068.pdf

Study of nuclear structure of 13C and 20Ne by low energy nuclear reactions

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