Abstract: Background: An accurate description of the initial and final state interactions in the 18O+76Se collision is demanded by the NUMEN project. The study of single and double charge exchange nuclear reactions is the main purpose for NUMEN, since these can be used as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To date, the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for the NUMEN double charge exchange studies are poorly known. The 18O+76Se case, here under study, is particularly relevant due to its connection with the 76Ge neutrinoless double-β decay. Purpose: In this work the authors want to characterize the initial-state interaction for the 18O+76Se reactions at 275 MeV incident energy determining the optical potential and evaluating the effect of couplings with the inelastic scattering on the elastic channel. Methods: The angular distributions of differential cross section were measured in the angular region between 4◦ and 22◦ in the center-of-mass reference frame. The cross sections were compared with theoretical calculations, that adopt different optical potentials. Coupling effects on the elastic channel were determined into the coupled channels formalism. Results: The excitation energy spectrum of the colliding nuclei and the cross section angular distributions were measured with satisfactory energy resolution. The elastic scattering cross section is not well reproduced in the full angular range explored when the optical model approach is adopted. A good agreement is found using coupled channel calculations. The initial state interaction for the 18O+76Se nuclear reactions at 275 MeV is determined. Conclusions: Coupled channels effects are crucial to obtain a good description of the measured elastic and inelastic channels cross sections, even at large transferred momenta where the optical model approach fails in reproducing the experimental data. The role of channel coupling could be relevant also in the analysis of other open reaction channels in the same collision and should be accounted for in double charge exchange analyses as well.

Palavras-Chave: oxygen 18; selenium 76; elastic scattering; inelastic scattering; nuclear reactions

LA FAUCI, L.; SPATAFORA, A.; CAPPUZZELLO, F.; AGODI, C.; CARBONE, D.; CAVALLARO, M.; LUBIAN, J.; ACOSTA, L.; AMADOR-VALENZUELA, P.; BORELLO-LEWIN, T.; BRISCHETTO, G.A.; CALABRESE, S.; CALVO, D.; CAPIROSSI, V.; CHAVEZ LOMELI, E.R.; CIRALDO, I.; CUTULI, M.; DELAUNAY, F.; DJAPO, H.; EKE, C.; FINOCCHIARO, P.; FIRAT, S.; FISICHELLA, M.; FOTI, A.; GUAZZELLI, M.A.; HACISALIHOGLU, A.; IAZZI, F.; LINARES, R.; MA, J.; MEDINA, N.H.; MORALLES, M.; OLIVEIRA, J.R.B.; PAKOU, A.; PANDOLA, L.; PETRASCU, H.; PINNA, F.; RIES, P.C.; RUSSO, G.; SGOUROS, O.; SOLAKCI, S.O.; SOUKERAS, V.; SOULIOTIS, G.; TORRESI, D.; TUDISCO, S.; WANG, J.; YANG, Y.; YILDIRIN, A.; ZAGATTO, V.A.B. 18O+76Se elastic and inelastic scattering at 275 MeV. Physical Review C, v. 104, n. 5, p. 054610-1 - 054610-9, 2021. DOI: 10.1103/PhysRevC.104.054610. Disponível em: http://repositorio.ipen.br/handle/123456789/32798. Acesso em: $DATA.

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Abstract: Background: Heavy-ion one-nucleon transfer reactions are promising tools to investigate single-particle configurations in nuclear states with and without the excitation of the core degrees of freedom. A careful determination of the spectroscopic amplitudes of these configurations is essential for the accurate study of other direct reactions as well as β decays. In nucleon transfer reactions core excitations, for both target and projectile systems, are best approached via coupled-channels reaction schemes. Despite being notoriously demanding in terms of computing resources, coupled-channels analyses are progressively becoming more affordable even within model spaces large enough for tackling medium mass nuclei. In this context, the 76Se(18O, 17O) 77Se reaction, here under study, gives a quantitative access to the relevant single-particle orbitals and core polarization configurations built on 76Se. This is particularly relevant, since it provides data-driven information to constrain nuclear structure models for 76Se, which is the daughter nucleus in the 76Ge ββ decay. This reaction is one of the systems studied in the frame of the Nuclear Matrix Elements for Neutrinoless double beta decay project. Purpose: We want to analyze transitions to low-lying excited states of the residual and ejectile nuclei in the 76Se(18O, 17O) 77Se one-neutron stripping reaction at 275-MeV incident energy and determine the role of single-particle and core excitation in the description of the measured cross sections. In addition, we explore the sensitivity of the calculated cross section to different nuclear structure models. Methods: The excitation energy spectrum and the differential cross-section angular distributions are measured using the MAGNEX large acceptance magnetic spectrometer for the detection of the ejectiles and the missing mass technique for the reconstruction of the reaction kinematics. The data are compared with calculations based on distorted-wave Born approximation, coupled-channels Born approximation, and coupled reaction channels adopting spectroscopic amplitudes for the projectile and target overlaps derived by large-scale shell-model calculations and interacting boson-fermion model. Results: Peaks in the energy spectra corresponding to groups of unresolved transitions to 77Se and 17O are identified. The experimental cross sections are extracted and compared to theoretical calculations. A remarkable agreement is found, without using any scaling factors, demonstrating that the adopted models for nuclear structure and reaction take into account the relevant aspects of the studied processes. The main transitions which contribute to the cross section of each peak are identified. Conclusions: The coupling with the inelastic channels feeding states in entrance and exit partitions is important in the one-neutron transfer reaction and should be accounted for in future analyses of other direct reactions such as single and double charge exchange processes involving 76Se isotope. The description of 77Se indicates the need of a large model space, in the view of an accurate description of the low-lying states, a feature that should be likely accounted even for ββ-decay studies of 76Ge.

Palavras-Chave: nuclear matrix; neutron transfer; double beta decay; oxygen 18; selenium 76

CIRALDO, I.; CAPPUZZELLO, F.; CAVALLARO, M.; CARBONE, D.; BURRELLO, S.; SPATAFORA, A.; GARGANO, A.; DE GREGORIO, G.; MAGANA VSEVOLODOVNA, R.I.; ACOSTA, L.; AGODI, C.; AMADOR-VALENZUELA, P.; BORELLO-LEWIN, T.; BRISCHETTO, G.A.; CALABRESE, S.; CALVO, D.; CAPIROSSI, V.; CHAVEZ LOMELI, E.R.; COLONNA, M.; DELAUNAY, F.; DJAPO, H.; EKE, C.; FINOCCHIARO, P.; FIRAT, S.; FISICHELLA, M.; FOTI, A.; HACISALIHOGLU, A.; IAZZI, F.; LA FAUCI, L.; LINARES, R.; MEDINA, N.H.; MORALLES, M.; OLIVEIRA, J.R.B.; PAKOU, A.; PANDOLA, L.; PETRASCU, H.; PINNA, F.; RUSSO, G.; SANTOPINTO, E.; SGOUROS, O.; GUAZZELLI, M.A.; SOLAKCI, S.O.; SOUKERAS, V.; SOULIOTIS, G.; TORRESI, D.; TUDISCO, S.; YILDIRIM, A.; ZAGATTO, V.A.B. Analysis of the one-neutron transfer reaction in 18O+76Se collisions at 275 MeV. Physical Review C, v. 105, n. 4, p. 044607-1 - 044607-15, 2022. DOI: 10.1103/PhysRevC.105.044607. Disponível em: http://repositorio.ipen.br/handle/123456789/33220. Acesso em: $DATA.

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Abstract: Nitrate stable isotopes provide information about nitrate contamination and cycling by microbial processes. The Fischa-Dagnitz (Austria) spring and river system in the agricultural catchment of the Vienna basin shows minor annual variance in nitrate concentrations. We measured nitrate isotopes (δ15N, δ18O) in the source spring and river up to the confluence with the Danube River (2019–2020) with chemical and water isotopes to assess mixing and nitrate transformation processes. The Fischa-Dagnitz spring showed almost stable nitrate concentration (3.3 ± 1.0 mg/l as NO3–-N) year-round but surprisingly variable δ15N, δ18O-NO3– values ranging from +5.5 to +11.1‰ and from +0.5 to +8.1‰, respectively. The higher nitrate isotope values in summer were attributed to release of older denitrified water from the spring whose isotope signal was dampened downstream by mixing. A mixing model suggested denitrified groundwater contributed > 50 % of spring discharge at baseflow conditions. The isotopic composition of NO3– in the gaining streams was partly controlled by nitrification during autumn and winter months and assimilation during the growing season resulting in low and high δ15N-NO3– values, respectively. NO3– isotope variation helped disentangle denitrified groundwater inputs and biochemical cycling processes despite minor variation of NO3– concentration.

Palavras-Chave: agriculture; biogeochemistry; denitrification; ground water; mixing; hydrology; isotopes; nitrogen 15; nitrates; oxygen 18

MATIATOS, IOANNIS; ARAGUAS-ARAGUAS, LUIS; WASSENAAR, LEONARD I.; MONTEIRO, LUCILENA R.; HARJUNG, ASTRID; DOUENCE, CEDRIC; KRALIK, MARTIN. Nitrate isotopes reveal N-cycled waters in a spring-fed agricultural catchment. Isotopes in Environmental and Health Studies, v. 59, n. 1, p. 27-47, 2023. DOI: 10.1080/10256016.2022.2157412. Disponível em: http://repositorio.ipen.br/handle/123456789/34010. Acesso em: $DATA.

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Abstract: The precise quasielastic excitation function for the 18O + 64Zn system was measured at energies near and below the Coulomb barrier at θlab = 161◦, from which its correlated quasielastic barrier distribution was derived. The excitation functions for the two-neutron, α, and tritium transfer reactions have also been measured at the same conditions. These data were well described by the coupled channel and coupled reaction channel calculations. The comparison of the data with theoretical calculations shows the strong influence of three inelastic channels in the coupling process: the quadrupole and octupole vibrational states of 64Zn, 2+ 1 and 3− 1 , and the quadrupole vibrational state of 18O, 2+ 1 . In addition, theoretical calculations indicate that the two-neutron stripping is mostly due to a one-step process, which has a striking effect on the reaction mechanism of this system.

Palavras-Chave: energy dependence; coulomb field; neutron transfer; zinc 64 target; oxygen 18; coupling; inelastic scattering; tritium; transfer reactions

CREMA, E.; PAES, B.; ZAGATTO, V.A.B.; HUIZA, J.F.P.; LUBIAN, J.; SHORTO, J.M.B.; SIMÕES, R.F.; MONTEIRO, D.S.; ADDED, N.; MORAIS, M.C.; GOMES, P.R.S. Strong neutron-transfer coupling effects in the reaction mechanism of the 18O + 64Zn system at energies near the Coulomb barrier. Physical Review C, v. 100, n. 5, p. 054608-1 - 054608-11, 2019. DOI: 10.1103/PhysRevC.100.054608. Disponível em: http://repositorio.ipen.br/handle/123456789/30851. Acesso em: $DATA.

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