Proton inelastic scattering reveals deformation in 8He

A measurement of proton inelastic scattering of 8He at 8.25A MeV at TRIUMF shows a resonance at 3.54(6) MeV with a width of 0.89(11) MeV. The energy of the state is in good agreement with coupled cluster and no-core shell model with continuum calculations, with the latter successfully describing the measured resonance width as well. Its differential cross section analyzed with phenomenological collective excitation form factor and microscopic coupled reaction channels framework consistently reveals a large deformation parameter = 0.40(3), consistent with no-core shell model predictions of a large neutron deformation. This deformed double-closed shell at the neutron drip-line opens a new paradigm.Oficina de Física Nuclear, Departamento de Energía de los EE. UU. DE-FG02-96ER40963 y DE-SC0018223Ministerio de Ciencia, Innovación y Universidades de España y Fondos FEDER de la U. E. FIS2017-88410-PUnión Europea. Programa Horizonte 2020, subvención n.º 654002

Excited states in neutron rich boron isotopes

Publisher's version/PDFNew experimental results on in-beam gamma spectroscopy of neutron rich boron isotopes are presented for [superscript 17]B and its neutron removal fragments [superscript 14,15]B, after scattering with a H[subscript 2] target. A gamma transition for [superscript 17]B is observed at 1089 [plus or minus] 15 keV. The fragment [superscript 15]B is observed abundantly associated with a gamma transition of 1336 [plus or minus] 10 keV. This suggests for the first time a core-excited structure for [superscript 17]B thereby providing a new insight into its structure. Observations for [superscript 12,14]B are also presented. The data set provides a useful systematic study of first excited states of neutron rich boron isotopes showing the dramatic drop in excitation energy beyond N = 8

Observation of large enhancements of charge exchange cross sections with neutron-rich carbon isotopes

Publisher's Version/PDFProduction cross sections of nitrogen isotopes from high-energy (∼950 MeV per nucleon) carbon isotopes on hydrogen and carbon targets have been measured for the first time for a wide range of isotopes (A = 12 to 19). The fragment separator FRS at GSI was used to deliver C-isotope beams. The cross sections of the production of N-isotopes were determined by charge measurements of forward-going fragments. The cross sections show a rapid increase with the number of neutrons in the projectile. Since the production of nitrogen is mostly due to charge-exchange (Cex) reactions below the proton separation energies, the present data suggests a concentration of Gamow–Teller and/or Fermi transition strength at low excitation energies for neutron-rich carbon isotopes. It was also observed that the Cex cross sections were enhanced much more strongly for neutron-rich isotopes in the C-target data

One-neutron removal reactions on Al isotopes around the N = 20 shell closure

Publisher's version/PDFThe one-neutron removal cross sections of neutron-rich Al isotopes and longitudinal momentum distributions of the residues have been measured for A = 33 to 36 at relativistic energies ([approximate to] 900 MeV/u). The inclusive data have been interpreted within the eikonal approximation. The evolution of the single-particle occupancy in the ground state of [superscript 33,34,35]Al has been studied and compared with shell model predictions. The inferred 2s[subscript 1/2] neutron occupancy in the [superscript 33]Al ground-state wave function is 20% to 40% lower than the predicted one. The inclusive data do not exclude the presence of intruder states. Some intruder l = 1 occupancy is found in [superscript 34]Al, similarly to [superscript 33]Mg. The single-particle 1f[subscript 7/2] occupancy shows a gradual increase at N = 22. Correspondingly, a decrease of the 1d[subscript 3/2] strength has been observed

Proton radius of Be-14 from measurement of charge-changing cross sections

Publisher's Version/PDFThe charge-changing cross sections of 7,9−12,14Be have been measured at 900A MeV on a carbon target. These cross sections are discussed both in terms of a geometrical and a Glauber model. From several different analyses of the cross sections, the proton distribution radius (proton radius) of 14Be is determined for the first time to be 2.41 ± 0.04 fm. A large difference in the proton and neutron radii is found. The proton radii are compared to the results of fermionic molecular dynamics (FMD) and antisymmetrized molecular dynamics (AMD) calculations

Systematic investigation of projectile fragmentation using beams of unstable B and C isotopes

Publisher's Version/PDFBackground: Models describing nuclear fragmentation and fragmentation fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool for reaching the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes. Method: We have measured projectile fragments from [superscript 10,12−18]C and [superscript 10−15]B isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent data set. We compare our data to model calculations. Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic [superscript 10,12−18]C and [superscript 10−15]B isotopes impinging on a carbon target. Comparing model calculations to the data, we find that the EPAX code is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease ABRABLA07 describes the data surprisingly well. Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data has allowed a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study

Evidence of soft dipole resonance in Li-11 with isoscalar character

Publisher's version/PDFThe first conclusive evidence of a dipole resonance in 11Li having isoscalar character observed from inelastic scattering with a novel solid deuteron target is reported. The experiment was performed at the newly commissioned IRIS facility at TRIUMF. The results show a resonance peak at an excitation energy of 1.03&nbsp;&plusmn; 0.03 MeV with a width of 0.51&nbsp;&plusmn; 0.11 MeV (FWHM). The angular distribution is consistent with a dipole excitation in the distorted-wave Born approximation framework. The observed resonance energy together with shell model calculations show the first signature that the monopole tensor interaction is important in 11Li. The first ab initio calculations in the coupled cluster framework are also presented.</p

Simultaneous analysis of the elastic scattering and breakup channel for the reaction Li-11 + Pb-208 at energies near the Coulomb barrier

Publisher's version/PDFWe present a detailed analysis of the elastic scattering and breakup channel for the reaction of [superscript 11]Li on [superscript 208]Pb at incident laboratory energies of 24.3 and 29.8 MeV, measured at the radioactive ion beam facility of TRIUMF, in Vancouver, Canada. A large yield of [superscript 9]Li fragments was detected by four charged particle telescopes in a wide angular range. The experimental angular and energy distributions of these [superscript 9]Li fragments have been compared to coupled-reaction-channel and continuum-discretized coupled-channel calculations. The large production of [superscript 9]Li fragments at small angles can be explained by considering a direct breakup mechanism, while at medium-large angles a competition between direct breakup and neutron transfer to the continuum of the [superscript 208]Pb target was observed

Coulomb dissociation of N 20,21

Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at