ELISSA is a new silicon-strip detector array under development at the Extreme Light Infrastructure - Nuclear Physics facility in collaboration with INFN-LNS, Catania. ELI-NP will provide very intense, brilliant gamma beams, tunable from 200keV to 19.5MeV. Several reactions important for the astrophysical p-process, Big Bang Nucleosynthesis and supernova explosion have been selected for the ﬁrst measurement campaigns starting in 2019

Balabanski, D. L.

La Cognata, M.

Matei, C.

Spitaleri, C.

Tesileanu, O.

Xu, Y.

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DOI 10.1393/ncc/i2016-16360-4Colloquia: SEA2016IL NUOVO CIMENTO 39 C (2016) 360Nuclear astrophysics measurements with ELISSA at ELI-NPC. Matei(1)(∗), D. L. Balabanski(1), O. Tesileanu(1), Y. Xu(1),M. La Cognata(2) and C. Spitaleri(2)(3)(1) Extreme Light Infrastructure, Nuclear Physics / Horia Hulubei National Institute for R&Din Physics and Nuclear Engineering - Bucharest-Magurele 077125, Romania(2) Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud - 95123 Catania, Italy(3) Dipartimento di Fisica ed Astronomia, Università di Catania - 95123 Catania, Italyreceived 28 November 2016Summary. — ELISSA is a new silicon-strip detector array under development atthe Extreme Light Infrastructure - Nuclear Physics facility in collaboration withINFN-LNS, Catania. ELI-NP will provide very intense, brilliant gamma beams,tunable from 200 keV to 19.5 MeV. Several reactions important for the astrophysicalp-process, Big Bang Nucleosynthesis and supernova explosion have been selected forthe first measurement campaigns starting in 2019.1. – IntroductionThe Extreme Light Infrastructure - Nuclear Physics (ELI-NP) facility, under con-struction in Bucharest-Magurele, Romania, consists of two major components: the HighPower Laser System and the Gamma Beam System (GBS) [1]. ELI-NP will allow eithercombined or stand-alone experiments using the high-power laser and the gamma beam.The GBS is an advanced source of gamma-ray photons able to produce beams ofmonochromatic and high spectral density gamma-ray photons. The gamma-ray beamis produced through Compton backscattering of laser light off an accelerated electronbeam. The GBS will consist of two stages: a low-energy stage in which gamma raysare produced with energies up to 3.5 MeV and a high-energy stage in which gammarays are produced with energies up to 19.5 MeV. The main specifications of the systemare: photon energy continuously tunable in the range 0.2–19.5 MeV, high degree of linearpolarization, better than 0.5% bandwidth, larger than 104 photons/s/eV spectral density,and source spot sizes of about 10–30 microns.(∗) E-mail: catalin.matei@eli-np.roCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 C. MATEI et al.Dedicated diagnostics systems for tuning and beam optimization are developed aftereach interaction point. Additional monitoring instruments will be associated with theexperimental stations for measuring the energy, intensity, and polarization of the gammabeam.2. – ELISSA developmentResistive-strip silicon detectors represent a good solution for detecting charged par-ticles as they provide good position resolution over a large solid angle with a relativelylimited channel count. A silicon array would make it possible to measure reactions onsolid targets and all the reactions on heavy nuclei intervening in the p-process. Resistive-strip silicon detector arrays have been successfully designed and commissioned for studiesof nuclear astrophysics reactions (e.g. ORRUBA [2]).The ELISSA array consists of X3 silicon-strip detectors (manufactured by MicronSemiconductor Ltd.) arranged into a barrel configuration [3]. The X3 is a 4-strip de-tector, 4 cm wide, position sensitive along the longitudinal axis (7.5 cm long), leadingto a position resolution better than 1 mm around 10 MeV. The barrel could be madeup of 3 rings of 12 position sensitive detectors, for a total angular coverage of 100◦ inthe laboratory system. This setup results in a very compact design with a good angularresolution. Since position is determined by charge partition, the number of electronicchannels is strongly reduced, as about 300 channels would be necessary for the wholebarrel. The angular coverage is extended by using end cap detectors such as the assemblyof four QQQ3 segmented detectors by Micron Semiconductor.3. – Experimental programSeveral reactions, including the 24Mg(γ, α)20Ne reaction, and their measurement withELISSA have been described in details in a published ELI-NP Technical Design Re-port [3]. Additional reactions are introduced in this section.3.1. The 7Li(γ, t)4He reaction. – One of the unresolved problems in nuclear astro-physics is the so-called “cosmological Li problem”. Big-Bang Nucleosynthesis (BBN)predicts the abundances of light elements 4He, D, 3He and 7Li that are produced shortlyafter the Big Bang. There is good agreement between calculated and observed abun-dances for all these light nuclei except for 7Li [4]. The calculated primordial abundanceof 7Li at WMAP baryonic density by Coc et al. [5] is between 4.56 and 5.34 × 10−10depending on the reaction network, while Cyburt et al. [6] has calculated a value of (5.24± 0.71) × 10−10. There is a factor of 3–4 discrepancy between the calculated primordialabundance at WMAP baryonic density and the observed abundance of 7Li.The most recent experimental measurements on 3H(α, γ)7Li are more than 30 yearsold. A recent compilation of the world data by Descouvemont et al. [7] points outconflicting results below 1 MeV and the lack of data above 1.2 MeV. The most recentand complete experimental data on the 3H(α, γ)7Li cross section at lower energies, Ecm ≤1.2MeV, have been measured at Caltech in 1992–1994 by Brune et al. [8]. The overallsystematic error in the measurement was estimated to be 6%.The mirror alpha capture reactions 3H(α, γ)7Li and 3He(α, γ)7Be are receiving a lotof theoretical attention recently [9] as theoretical models could provide the capture crosssection at solar energies where experimental measurements are not possible. Neff [9] hasNUCLEAR ASTROPHYSICS MEASUREMENTS WITH ELISSA AT ELI-NP 3Fig. 1. – Calculated 3H(α, γ)7Li S-factor. Various radiative capture contributions are showntogether with direct capture.calculated the radiative capture cross sections for the 3He(α, γ)7Be and 3H(α, γ)7Li re-actions in the fully microscopic fermionic molecular dynamics approach using a realisticeffective interaction. The calculations are in good agreement with recent measurementsof 3He(α, γ)7Be below 3 MeV center-of-mass energy, describing well the energy depen-dance and the absolute normalization of the capture cross section. The author points outthat a model which successfully describes 3He(α, γ)7Be should also perform well for the3H(α, γ)7Li cross section. A comparison with the experimental data of Brune et al. [8]reveals a good agreement on the energy dependence but the absolute normalization isabout 15% larger, much more than the experimental uncertainties. With the exten-sive measurements of the 3He(α, γ)7Be reaction, the best contender for an experimentaldiscrepancy is the 3H(α, γ)7Li reaction.The total cross section for 3H(α, γ)7Li in the energy range of 4MeV ≤ Eγ ≤ 11MeVhas been calculated by using the contributions from both direct capture and the com-pound capture of 7 resonant state. With the R-matrix code AZURE2 [10], the compoundcapture cross section from the 7 resonant states is calculated (fig. 1).The primary goal of the measurement is to determine the cross sections and angulardistributions for the 7Li(γ, t)4He reaction at γ energies between 4 and 11 MeV. A MonteCarlo simulation based on GEANT4 has been developed to study the influence of targetthickness on the count rate and separation of the tritons and α-particles. The resultsshow that the optimal target thickness is 150 μg/cm2 for 7Li and 400μg/cm2 for 7LiF.Additional simulations using the VIKAR code developed by Pain [11] show that targeteffects are important and separation of tritons and alpha particles is difficult below 4 MeV.A thinner target, 100μg/cm2 of 7Li, is more suitable at lower energies (fig. 2).Assuming a maximum γ-beam flux of 109 s−1 at ELI-NP, we estimate to measure anyoff-resonance points in about 10 minutes with good statistical precision for both crosssection and angular distribution measurements. Measurements above 7–8 MeV would bean ideal first day experiment with ELISSA at ELI-NP.4 C. MATEI et al.Fig. 2. – Simulated energy vs. angle spectrum for tritons and alpha particles for Eγ = 5 MeVand a target thicknesses of 100 μg/cm2 using the VIKAR code. Tritons are shown in black,α-particles in red.3.2. P-process reactions. – In stellar explosive sites like supernovae, the astrophysicalp-process is an important way of nucleosynthesis to produce the proton-rich, stable nu-clides beyond Fe which cannot be reached by the s- and r-processes [12]. It is thought thatthese nuclides are synthesized by photodisintegration of pre-existing s- and r-processesnuclei. The p-process contains capture and photodisintegration reactions for about 2000proton-rich and stable nuclei beyond Fe. For most of them, experimental data are notavailable. There are 35 nuclides classified as the p-process nuclides ranging from 74Se to196Hg that are produced by re-processing the pre-existing seed nuclei. P-nuclei of Moand Ru are produced only by p-process in the scenario of supernova explosion. Astro-physical simulations show that the nucleosynthesis of 92,94Mo and 96,98Ru are system-atically underproduced, by benchmarking the predicted abundances of these nuclei totheir corresponding abundances observed in the Solar System composition. Therefore,it is expected that to experimentally determine the astrophysical reaction rates aroundMo and Ru would remedy this unsolved problem of p-process nucleosynthesis [13]. Theisotopes of Sm are also predicted to be produced by photodisintegration reactions withinthe p-process. It has been pointed out that the 146Sm would be a potential p-processchronometer, which could constrain the chemical evolution in the solar nebula and earlyplanetary bodies. All these reactions proposed to be measured at ELI-NP have thepotential to solve important astrophysical issues in the p-process.∗ ∗ ∗CM, DLB, OT, and YX were supported in part by Extreme Light InfrastructureNuclear Physics (ELI-NP) Phase I, a project co-financed by the European Union throughthe European Regional Development Fund.NUCLEAR ASTROPHYSICS MEASUREMENTS WITH ELISSA AT ELI-NP 5REFERENCES[1] Zamfir N. V., EPJ Web of Conf., 66 (2014) 11043.[2] Pain S. D. et al., Nucl. Instrum. Methods. Phys. Res. B, 261 (2007) 1122.[3] Tesileanu O. et al., Rom. Rep. Phys., 68 (2016) S699.[4] Fields B. D., Annu. Rev. Nucl. Part. Sci., 61 (2011) 47.[5] Coc A. et al., J. Cosmol. Astropart. Phys., 10 (2014) 50.[6] Cyburt R. H. et al., JCAP, 11 (2008) 12.[7] Descouvemont P. et al., At. Data Nucl. Data Tables, 88 (2004) 203.[8] Brune C. R., Kavanagh R. W. and Rolfs C., Phys. Rev. C., 50 (1994) 2005.[9] Neff T., Phys. Rev. Lett., 106 (2011) 042502.[10] Azure2, azure.nd.edu[11] Pain S. D., VIKAR 4.0, https://sites.google.com/a/nuclearemail.org/vikar/[12] Iliadis C., Nuclear Physics of Stars, (Wiley-VCH Verlag) 2007.[13] Rapp W. et al., Nucl. Phys. A, 758 (2005) 545.

Nuclear astrophysics measurements with ELISSA at ELI-NP

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Nuclear astrophysics measurements with ELISSA at ELI-NP

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