P. Golubev - Academia.edu (original) (raw)

Papers by P. Golubev

Physical review letters, Jan 25, 2016

The ^{54}Fe nucleus was populated from a ^{56}Fe beam impinging on a Be target with an energy of ... more The ^{54}Fe nucleus was populated from a ^{56}Fe beam impinging on a Be target with an energy of E/A=500 MeV. The internal decay via γ-ray emission of the 10^{+} metastable state was observed. As the structure of this isomeric state has to involve at least four unpaired nucleons, it cannot be populated in a simple two-neutron removal reaction from the ^{56}Fe ground state. The isomeric state was produced in the low-momentum (-energy) tail of the parallel momentum (energy) distribution of ^{54}Fe, suggesting that it was populated via the decay of the Δ^{0} resonance into a proton. This process allows the population of four-nucleon states, such as the observed isomer. Therefore, it is concluded that the observation of this 10^{+} metastable state in ^{54}Fe is a consequence of the quark structure of the nucleons.

Frontiers in Chemistry

Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its inter... more Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its interaction with gold was investigated in two gas-solid chromatography experiments, which reported two different types of interaction, however, each based on the level of a few registered atoms only. Whereas noble-gas-like properties were suggested from the first experiment, the second one pointed at a volatile-metal-like character. Here, we present further experimental data on adsorption studies of Fl on silicon oxide and gold surfaces, accounting for the inhomogeneous nature of the surface, as it was used in the experiment and analyzed as part of the reported studies. We confirm that Fl is highly volatile and the least reactive member of group 14. Our experimental observations suggest that Fl exhibits lower reactivity towards Au than the volatile metal Hg, but higher reactivity than the noble gas Rn.

Proceedings of the Conference on Advances in Radioactive Isotope Science (ARIS2014), 2015

The excitation function of the proton resonance elastic scattering with a 30 Mg beam of 2.92 MeV/... more The excitation function of the proton resonance elastic scattering with a 30 Mg beam of 2.92 MeV/nucleon was measured around 0 degrees in the laboratory frame. Three resonances corresponding to high excited states in 31 Al were successfully observed. They correspond to the isobaric analog resonances of the first three bound states in 31 Mg, which is considered to be located at the border of the island of inversion. An R-matrix analysis on the excitation function revealed that the spectroscopic factors for the first two positive parity resonances were quenched compared to those for other N=19 nuclei, 35 S and 37 Al, clearly indicating that the shell structure changes between 30 Mg and 31 Mg.

D. Cortina-Gil ∗1, H. Alvarez-Pol 1, T. Aumann13, V. Avdeichikov 4, M. Bendel†7, J. Benlliure1, D... more D. Cortina-Gil ∗1, H. Alvarez-Pol 1, T. Aumann13, V. Avdeichikov 4, M. Bendel†7, J. Benlliure1, D. Bertini5, A. Bezbakh 11, T. Bloch13, M. Böhmer7, M.J.G. Borge2, J.A. Briz2, P. Cabanelas 1, E. Casarejos 8, M. Carmona Gallardo2, J. Cederk̈all4, L. Chulkov12, M. Dierigl7, D. Di Julio4, G. Ferńandez Maŕ ınez13, E. Fiori10, A. Fomichev 11, D. Galaviz9, R. Gernḧauser7, J. Gerl5, P. Golubev4, M. Golovkov11, D. Gonźalez1, A. Gorshkov 11, A.L. Hartig13, A. Heinz3, M. Heil5, B. Heiss7, A. Ignatov13, B. Jakobsson 4, H.T. Johansson 3, P. Klenze7, D. Köeper5, Th. Kröll13, R. Krücken‡7, S. Krupko11, F. Kurz7, T. Le Bleis7, B. Löher10, E. Nacher 2, T. Nilsson3, A. Perea2, C. Pfeffer7, B. Pietras1, R. Reifarth6, P. Remmels 7, H.B. Rhee13, J. Sanchez del Rio 2, D. Savran10, H. Scheit 13, S. Sidorchuk 11, H. Simon5, O. Tengblad2, P. Teubig9, R. Thies3, J.A. Viĺan8, M. von Schmid13, M. Winkel§7, S. Winkler 7, F. Wamers13, P. Yãnez8, and the RB collaboration. 1Universidad de Santiago de Compostela; 2...

J. Khuyagbaatar1,2, A. Yakushev1, Ch.E. Dullmann1,2,3, H. Nitsche4, J. Roberto5, D. Ackermann1, L... more J. Khuyagbaatar1,2, A. Yakushev1, Ch.E. Dullmann1,2,3, H. Nitsche4, J. Roberto5, D. Ackermann1, L.-L. Andersson2, M. Asai6, H. Brand1, M. Block1, D.M. Cox7, M. Dasgupta8, X. Derkx2,3, A. Di Nitto3, J. Dvorak2, K. Eberhardt2,3, P.A. Ellison4, N.E. Esker4, J. Even2,3, M. Evers8, C. Fahlander9, U. Forsberg9, J.M. Gates4, N. Gharibyan10, K.E. Gregorich4, P. Golubev9, O. Gothe4, J.H. Hamilton11, D.J. Hinde8, W. Hartmann1, R.-D. Herzberg7, F.P. Hesberger1,2, J. Hoffmann1, R. Hollinger1, A. Hubner1, E. Jager1, J. Jeppsson9, B. Kindler1, S. Klein3, I. Kojouharov1, J.V. Kratz3, J. Krier1, N. Kurz1, S. Lahiri12, B. Lommel1, M. Maiti12, K. Miernik5, S. Minami1, A. Mistry7, C. Mokry2,3, J.P. Omtvedt13, G.K. Pang4, P. Papadakis7, I. Pysmenetska1, D. Renisch3, D. Rudolph9, J. Runke1, K. Rykaczewski5, L.G. Sarmiento9, M. Schadel1,6, B. Schausten1, D.A. Shaughnessy10, A. Semchenkov13, J. Steiner1, P. Steinegger14, P. Thorle-Pospiech2,3, E.E. Tereshatov10, T. Torres De Heidenreich1, N. Trautmann3, A...

DSSSD detectors are constructed as large area silicon diodes with electrically segmented p and n-... more DSSSD detectors are constructed as large area silicon diodes with electrically segmented p and n-side contacts. Signals are read out on both, p and n-side simultaneously. The segmentation is usually such that there are unique intersection points of opposite side’s contacts, the measure ment of one p and on n-side signal allows to reconstruct the two dimensional spatial position of an event inside the detector.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2021

Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUT... more Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUTs) are presented. The LUTs were derived from the topography of a polished and a lapped surface of a CsI(Tl) crystal measured with atomic force microscopy. Simulations with different combinations of polished and lapped surfaces were performed, to extract the non-uniformity of light collection depending on the interaction point, and compared to experimental results. The simulations reproduce the general trend given by the measurements, and show that more homogeneous light collection is attained when all lateral sides of the crystal are lapped. For the lapped crystal the simulation model is most sensitive to the reflectivity of the enhanced specular reflector (ESR) foil surrounding the crystal, which is one of several properties influencing the light transport examined in this study. The sensitivity of the light-output non-uniformity to variations in the absorption length observed in a batch of CsI(Tl) crystals in a previous study is also discussed. Residual differences between the simulation and the measurements can potentially be attributed to the scattering of scintillation photons inside the materials used. Additional measurements to further advance the construction of the simulation model are suggested.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2020

One of the factors that can contribute to the resolution of long, doped inorganic scintillators u... more One of the factors that can contribute to the resolution of long, doped inorganic scintillators used for nuclear spectroscopy is the variation of the dopant concentration over the length the detector crystal. In this work an investigation of such potential variations in one of the CsI(Tl) scintillators used in the calorimeter, CALIFA, of the R 3 B experiment at FAIR, has been performed using particle induced X-ray emission. No statistically significant gradient in doping level was found along the long axis of the investigated sample crystal and the mean value of the Tl concentration was measured to be 0.0839(38)% by weight. This corresponds to a light output of 97.3 +1.3 −1.7 % relative to the maximum attainable light output according to previously published work. By taking the ±1 bounds, the 3% statistical spread in the relative light output provides a good reference value of the minimum light-output non-uniformity observed for the CALIFA crystals. If the relative light output is estimated pointwise from a set of Tl concentration measurements a light-output non-uniformity of 4.6(2.4)% results. For a-ray energy of 662 keV the deduced variation in Tl concentration contributes with 0.48(6)% to the typical resolution of 7.74(6)% measured with a collimated source along the crystal main axis. The result is of interest for the characterization of the detector system performance and for realistic simulations of the light collection process in detector systems that are used for nuclear spectroscopy and calorimetry.

Journal of Physics: Conference Series, 2020

CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, i... more CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, intended for detecting high energy charged particles and γ-rays in inverse kinematics direct reactions. It surrounds the reaction target in a segmented configuration of Barrel and Forward End-Cap pieces. The CALIFA Barrel consists of 1952 detection units made of CsI(Tl) long-shaped scintillator crystals, and it is being commissioned during the Phase0 experiments at FAIR. The first setup for the CALIFA Barrel commissioning is presented here. Results of detector performance with γ-rays are obtained, and show that the system fulfills the design requirements.

The European Physical Journal A, 2020

A first performance test of the Coulomb excitation multipolarimetry (Coulex-multipolarimetry) met... more A first performance test of the Coulomb excitation multipolarimetry (Coulex-multipolarimetry) method is presented. It is based on a 85 Br πp 3/2 → πp 1/2 spin-flip experiment performed as part of the PreSPEC-AGATA campaign at the GSI Helmholtzzentrum für Schwerionenforschung (GSI). Via determination of background levels around the expected 85 Br excitations as well as measured 197 Au excitations, an upper limit for the M 1 transition strength of the 1/2 − 1 → 3/2 − g.s. transition in 85 Br and a lower beam time limit for upcoming experimental campaigns utilizing Coulex-multipolarimetry have been inferred. The impact of the use of AGATA in its anticipated 1π configuration on these estimates is deduced via Geant4 simulations.

The European Physical Journal A, 2020

Several experiments were conducted at the 10 MV Van-de-Graaff tandem accelerator at the Institute... more Several experiments were conducted at the 10 MV Van-de-Graaff tandem accelerator at the Institute of Nuclear Physics, Cologne, to detect proton emission from the isomeric 6457-keV 10^+$$10+ state in ^{54}\hbox {Ni}$$54Ni. Excitation functions for two fusion–evaporation reactions were measured to maximise the population of the rare two-neutron evaporation channel from a ^{56}\hbox {Ni}$$56Ni compound nucleus. The search for delayed proton emission was based on the ^{28}\hbox {Si}$$28Si($$^{28}\hbox {Si},2n$$28Si,2n)$$^{54}\hbox {Ni}$$54Ni reaction at a beam energy of 70 MeV. For this reaction, a cross-section limit for the population of the 10^+$$10+ state in ^{54}\hbox {Ni}$$54Ni and its proton-decay branch was determined to be \sigma < 22$$σ<22 nb.

Physical Review C, 2017

Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study prot... more Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The 26 F nucleus, composed of a deeply bound π0d 5/2 proton and an unbound ν0d 3/2 neutron on top of an 24 O core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J π = 1 + 1 − 4 + 1 multiplet. Energies of observed states in 25,26 F have been compared to calculations using the independent-particle shell model, a phenomenological shell-model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton-neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need of implementing the role of the continuum in theoretical descriptions, or to a wrong determination of the atomic mass of 26 F.

Physics Letters B, 2018

collisions or quasifission. The present observations are discussed within the framework of two-bo... more collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.

Physical Review Letters, 2018

The emission of neutron pairs from the neutron-rich N = 12 isotones 18 C and 20 O has been studie... more The emission of neutron pairs from the neutron-rich N = 12 isotones 18 C and 20 O has been studied by high-energy nucleon knockout from 19 N and 21 O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay 19 N(−1p) 18 C * → 16 C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a 14 C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay 21 O(−1n) 20 O * → 18 O+n+n, attributed to its formation through the knockout of a deeply-bound neutron that breaks the 16 O core and reduces the number of pairs.

Physical review letters, Jan 25, 2016

The ^{54}Fe nucleus was populated from a ^{56}Fe beam impinging on a Be target with an energy of ... more The ^{54}Fe nucleus was populated from a ^{56}Fe beam impinging on a Be target with an energy of E/A=500 MeV. The internal decay via γ-ray emission of the 10^{+} metastable state was observed. As the structure of this isomeric state has to involve at least four unpaired nucleons, it cannot be populated in a simple two-neutron removal reaction from the ^{56}Fe ground state. The isomeric state was produced in the low-momentum (-energy) tail of the parallel momentum (energy) distribution of ^{54}Fe, suggesting that it was populated via the decay of the Δ^{0} resonance into a proton. This process allows the population of four-nucleon states, such as the observed isomer. Therefore, it is concluded that the observation of this 10^{+} metastable state in ^{54}Fe is a consequence of the quark structure of the nucleons.

Frontiers in Chemistry

Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its inter... more Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its interaction with gold was investigated in two gas-solid chromatography experiments, which reported two different types of interaction, however, each based on the level of a few registered atoms only. Whereas noble-gas-like properties were suggested from the first experiment, the second one pointed at a volatile-metal-like character. Here, we present further experimental data on adsorption studies of Fl on silicon oxide and gold surfaces, accounting for the inhomogeneous nature of the surface, as it was used in the experiment and analyzed as part of the reported studies. We confirm that Fl is highly volatile and the least reactive member of group 14. Our experimental observations suggest that Fl exhibits lower reactivity towards Au than the volatile metal Hg, but higher reactivity than the noble gas Rn.

Proceedings of the Conference on Advances in Radioactive Isotope Science (ARIS2014), 2015

The excitation function of the proton resonance elastic scattering with a 30 Mg beam of 2.92 MeV/... more The excitation function of the proton resonance elastic scattering with a 30 Mg beam of 2.92 MeV/nucleon was measured around 0 degrees in the laboratory frame. Three resonances corresponding to high excited states in 31 Al were successfully observed. They correspond to the isobaric analog resonances of the first three bound states in 31 Mg, which is considered to be located at the border of the island of inversion. An R-matrix analysis on the excitation function revealed that the spectroscopic factors for the first two positive parity resonances were quenched compared to those for other N=19 nuclei, 35 S and 37 Al, clearly indicating that the shell structure changes between 30 Mg and 31 Mg.

D. Cortina-Gil ∗1, H. Alvarez-Pol 1, T. Aumann13, V. Avdeichikov 4, M. Bendel†7, J. Benlliure1, D... more D. Cortina-Gil ∗1, H. Alvarez-Pol 1, T. Aumann13, V. Avdeichikov 4, M. Bendel†7, J. Benlliure1, D. Bertini5, A. Bezbakh 11, T. Bloch13, M. Böhmer7, M.J.G. Borge2, J.A. Briz2, P. Cabanelas 1, E. Casarejos 8, M. Carmona Gallardo2, J. Cederk̈all4, L. Chulkov12, M. Dierigl7, D. Di Julio4, G. Ferńandez Maŕ ınez13, E. Fiori10, A. Fomichev 11, D. Galaviz9, R. Gernḧauser7, J. Gerl5, P. Golubev4, M. Golovkov11, D. Gonźalez1, A. Gorshkov 11, A.L. Hartig13, A. Heinz3, M. Heil5, B. Heiss7, A. Ignatov13, B. Jakobsson 4, H.T. Johansson 3, P. Klenze7, D. Köeper5, Th. Kröll13, R. Krücken‡7, S. Krupko11, F. Kurz7, T. Le Bleis7, B. Löher10, E. Nacher 2, T. Nilsson3, A. Perea2, C. Pfeffer7, B. Pietras1, R. Reifarth6, P. Remmels 7, H.B. Rhee13, J. Sanchez del Rio 2, D. Savran10, H. Scheit 13, S. Sidorchuk 11, H. Simon5, O. Tengblad2, P. Teubig9, R. Thies3, J.A. Viĺan8, M. von Schmid13, M. Winkel§7, S. Winkler 7, F. Wamers13, P. Yãnez8, and the RB collaboration. 1Universidad de Santiago de Compostela; 2...

J. Khuyagbaatar1,2, A. Yakushev1, Ch.E. Dullmann1,2,3, H. Nitsche4, J. Roberto5, D. Ackermann1, L... more J. Khuyagbaatar1,2, A. Yakushev1, Ch.E. Dullmann1,2,3, H. Nitsche4, J. Roberto5, D. Ackermann1, L.-L. Andersson2, M. Asai6, H. Brand1, M. Block1, D.M. Cox7, M. Dasgupta8, X. Derkx2,3, A. Di Nitto3, J. Dvorak2, K. Eberhardt2,3, P.A. Ellison4, N.E. Esker4, J. Even2,3, M. Evers8, C. Fahlander9, U. Forsberg9, J.M. Gates4, N. Gharibyan10, K.E. Gregorich4, P. Golubev9, O. Gothe4, J.H. Hamilton11, D.J. Hinde8, W. Hartmann1, R.-D. Herzberg7, F.P. Hesberger1,2, J. Hoffmann1, R. Hollinger1, A. Hubner1, E. Jager1, J. Jeppsson9, B. Kindler1, S. Klein3, I. Kojouharov1, J.V. Kratz3, J. Krier1, N. Kurz1, S. Lahiri12, B. Lommel1, M. Maiti12, K. Miernik5, S. Minami1, A. Mistry7, C. Mokry2,3, J.P. Omtvedt13, G.K. Pang4, P. Papadakis7, I. Pysmenetska1, D. Renisch3, D. Rudolph9, J. Runke1, K. Rykaczewski5, L.G. Sarmiento9, M. Schadel1,6, B. Schausten1, D.A. Shaughnessy10, A. Semchenkov13, J. Steiner1, P. Steinegger14, P. Thorle-Pospiech2,3, E.E. Tereshatov10, T. Torres De Heidenreich1, N. Trautmann3, A...

DSSSD detectors are constructed as large area silicon diodes with electrically segmented p and n-... more DSSSD detectors are constructed as large area silicon diodes with electrically segmented p and n-side contacts. Signals are read out on both, p and n-side simultaneously. The segmentation is usually such that there are unique intersection points of opposite side’s contacts, the measure ment of one p and on n-side signal allows to reconstruct the two dimensional spatial position of an event inside the detector.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2021

Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUT... more Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUTs) are presented. The LUTs were derived from the topography of a polished and a lapped surface of a CsI(Tl) crystal measured with atomic force microscopy. Simulations with different combinations of polished and lapped surfaces were performed, to extract the non-uniformity of light collection depending on the interaction point, and compared to experimental results. The simulations reproduce the general trend given by the measurements, and show that more homogeneous light collection is attained when all lateral sides of the crystal are lapped. For the lapped crystal the simulation model is most sensitive to the reflectivity of the enhanced specular reflector (ESR) foil surrounding the crystal, which is one of several properties influencing the light transport examined in this study. The sensitivity of the light-output non-uniformity to variations in the absorption length observed in a batch of CsI(Tl) crystals in a previous study is also discussed. Residual differences between the simulation and the measurements can potentially be attributed to the scattering of scintillation photons inside the materials used. Additional measurements to further advance the construction of the simulation model are suggested.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2020

One of the factors that can contribute to the resolution of long, doped inorganic scintillators u... more One of the factors that can contribute to the resolution of long, doped inorganic scintillators used for nuclear spectroscopy is the variation of the dopant concentration over the length the detector crystal. In this work an investigation of such potential variations in one of the CsI(Tl) scintillators used in the calorimeter, CALIFA, of the R 3 B experiment at FAIR, has been performed using particle induced X-ray emission. No statistically significant gradient in doping level was found along the long axis of the investigated sample crystal and the mean value of the Tl concentration was measured to be 0.0839(38)% by weight. This corresponds to a light output of 97.3 +1.3 −1.7 % relative to the maximum attainable light output according to previously published work. By taking the ±1 bounds, the 3% statistical spread in the relative light output provides a good reference value of the minimum light-output non-uniformity observed for the CALIFA crystals. If the relative light output is estimated pointwise from a set of Tl concentration measurements a light-output non-uniformity of 4.6(2.4)% results. For a-ray energy of 662 keV the deduced variation in Tl concentration contributes with 0.48(6)% to the typical resolution of 7.74(6)% measured with a collimated source along the crystal main axis. The result is of interest for the characterization of the detector system performance and for realistic simulations of the light collection process in detector systems that are used for nuclear spectroscopy and calorimetry.

Journal of Physics: Conference Series, 2020

CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, i... more CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, intended for detecting high energy charged particles and γ-rays in inverse kinematics direct reactions. It surrounds the reaction target in a segmented configuration of Barrel and Forward End-Cap pieces. The CALIFA Barrel consists of 1952 detection units made of CsI(Tl) long-shaped scintillator crystals, and it is being commissioned during the Phase0 experiments at FAIR. The first setup for the CALIFA Barrel commissioning is presented here. Results of detector performance with γ-rays are obtained, and show that the system fulfills the design requirements.

The European Physical Journal A, 2020

A first performance test of the Coulomb excitation multipolarimetry (Coulex-multipolarimetry) met... more A first performance test of the Coulomb excitation multipolarimetry (Coulex-multipolarimetry) method is presented. It is based on a 85 Br πp 3/2 → πp 1/2 spin-flip experiment performed as part of the PreSPEC-AGATA campaign at the GSI Helmholtzzentrum für Schwerionenforschung (GSI). Via determination of background levels around the expected 85 Br excitations as well as measured 197 Au excitations, an upper limit for the M 1 transition strength of the 1/2 − 1 → 3/2 − g.s. transition in 85 Br and a lower beam time limit for upcoming experimental campaigns utilizing Coulex-multipolarimetry have been inferred. The impact of the use of AGATA in its anticipated 1π configuration on these estimates is deduced via Geant4 simulations.

The European Physical Journal A, 2020

Several experiments were conducted at the 10 MV Van-de-Graaff tandem accelerator at the Institute... more Several experiments were conducted at the 10 MV Van-de-Graaff tandem accelerator at the Institute of Nuclear Physics, Cologne, to detect proton emission from the isomeric 6457-keV 10^+$$10+ state in ^{54}\hbox {Ni}$$54Ni. Excitation functions for two fusion–evaporation reactions were measured to maximise the population of the rare two-neutron evaporation channel from a ^{56}\hbox {Ni}$$56Ni compound nucleus. The search for delayed proton emission was based on the ^{28}\hbox {Si}$$28Si($$^{28}\hbox {Si},2n$$28Si,2n)$$^{54}\hbox {Ni}$$54Ni reaction at a beam energy of 70 MeV. For this reaction, a cross-section limit for the population of the 10^+$$10+ state in ^{54}\hbox {Ni}$$54Ni and its proton-decay branch was determined to be \sigma < 22$$σ<22 nb.

Physical Review C, 2017

Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study prot... more Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The 26 F nucleus, composed of a deeply bound π0d 5/2 proton and an unbound ν0d 3/2 neutron on top of an 24 O core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J π = 1 + 1 − 4 + 1 multiplet. Energies of observed states in 25,26 F have been compared to calculations using the independent-particle shell model, a phenomenological shell-model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton-neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need of implementing the role of the continuum in theoretical descriptions, or to a wrong determination of the atomic mass of 26 F.

Physics Letters B, 2018

collisions or quasifission. The present observations are discussed within the framework of two-bo... more collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.

Physical Review Letters, 2018

The emission of neutron pairs from the neutron-rich N = 12 isotones 18 C and 20 O has been studie... more The emission of neutron pairs from the neutron-rich N = 12 isotones 18 C and 20 O has been studied by high-energy nucleon knockout from 19 N and 21 O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay 19 N(−1p) 18 C * → 16 C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a 14 C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay 21 O(−1n) 20 O * → 18 O+n+n, attributed to its formation through the knockout of a deeply-bound neutron that breaks the 16 O core and reduces the number of pairs.