Nuclear Experiment

Collinear laser spectroscopy measurements were performed on 69,71,73 Ge isotopes ( Z=32 ) at ISOLDE-CERN. The hyperfine structure of the 4 s 2 4 p 2 3 P 1 →4 s 2 4p5s 3 P o 1 transition of the germanium atom was probed with laser light of 269 nm, produced by combining the frequency-mixing and frequency-doubling techniques. The hyperfine fields for both atomic levels were calculated using state-of-the-art atomic relativistic Fock-space coupled-cluster calculations. A new 73 Ge quadrupole moment was determined from these calculations and previously measured precision hyperfine parameters, yielding Q s = − 0.198(4) b, in excellent agreement with the literature value from molecular calculations. The moments of 69 Ge have been revised: μ = +0.920(5) μ N and Q s = +0.114(8) b, and those of 71 Ge have been confirmed. The experimental moments around N=40 are interpreted with large-scale shell-model calculations using the JUN45 interaction, revealing rather mixed wave function configurations, although their g -factors are lying close to the effective single-particle values. Through a comparison with neighboring isotones, the structural change from the single-particle nature of nickel to deformation in germanium is further investigated around N=40 .

Neutrinoless double beta-decay(DBD) is of current interest in high-sensitivity frontiers of particle physics. The decay is very sensitive to Majorana neutrinos masses, neutrino CP phases, right-handed weak interactions and others, which are beyond the standard electro-weal model. DBDs are actually ultra-rare events, and thus DBD experiments with ultra-high sensitivity are required. Critical discussions are presented on nuclear and detector sensitivities for high-sensitivity DBD experiments to study the neutrino masses in the normal and inverted hierarchies.

The nuclear level density of 115 Sn has been measured in an excitation energy range of ∼ 2 - 9 MeV using the experimental neutron evaporation spectra from the 115 In( p,n ) 115 Sn reaction. The experimental level densities were compared with the microscopic Hartree-Fock BCS (HFBCS), Hartree-Fock-Bogoliubov plus combinatorial (HFB+C), and an exact pairing plus independent particle model (EP+IPM) calculations. It is observed that the EP+IPM provides the most accurate description of the experimental data. The thermal properties (entropy and temperature) of 115 Sn have been investigated from the measured level densities. The experimental temperature profile as well as the calculated heat capacity show distinct signatures of a transition from the strongly-paired nucleonic phase to the weakly paired one in this nucleus.

Evaporated α -spectra have been measured in coincidence with low energy discrete γ -rays from residual nucleus 68 Zn populated in the reaction 64 Ni( 9 Be, α n) 68 Zn at E ( 9 Be) = 30 MeV producing 73 Ge compound nucleus. Low energy γ -gated α -particle spectra, for the first time, have been used to extract the nuclear level density (NLD) for the intermediate 69 Zn nucleus in the excitation energy range of E ≈ 5-20 MeV. The slope of NLD as a function of excitation energy for 69 Zn matches nicely with the slope determined from RIPL estimates for NLD at low energies and the NLD from neutron resonance data. Extracted inverse NLD parameter (k = A/ a ˜ ) has been used to determine the nuclear level density parameter value a at neutron separation energy S n for 69 Zn. Total cross-section of 68 Zn(n, γ ) capture reaction as a function of neutron energy is then estimated employing the derived a( S n ) in the reaction code TALYS. It is found that the estimated neutron capture cross-section agrees well with the available experimental data without any normalization. The present result indicates that experimentally derived nuclear level density parameter can constrain the statistical model description of astrophysical capture cross-section and optimize the uncertainties associated with the astrophysical reaction rate

The absolute differential cross sections for small-angle proton elastic scattering off the nuclei 12,14??7 C have been measured in inverse kinematics at energies near 700 MeV/u at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR served simultaneously as a gas target and a detector for the recoil protons. The projectile scattering angles were measured with multi-wire tracking detectors. The radial nuclear matter density distributions and the root-mean-square nuclear matter radii were deduced from the measured cross sections using the Glauber multiple-scattering theory. A possible neutron halo structure in 15 C, 16 C and 17 C is discussed. The obtained data show evidence for a halo structure in the 15 C nucleus.

We present the analyses of single electrons from semileptonic bottom and charm hadron decays at mid-rapidity in s NN − − − − √ = 200 and 54.4 GeV Au+Au collisions (talk in Heavy-Flavor session III). The data at s NN − − − − √ = 200 GeV incorporate information from the Heavy Flavor Tracker which enables the topological separation of electrons originating from bottom and charm hadron decays. We report the first STAR measurements at s NN − − − − √ = 200 GeV of v 2 for bottom decay electrons as a function of p T and v 1 for charm decay electrons as a function of electron rapidity. Additionally, we present the improved measurements of heavy-flavor decay electron R AA and a new measurement of the ratio of R CP between bottom and charm decay electrons. Finally, we also report the measurement of non-photonic electron v 2 in s NN − − − − √ = 54.4 GeV data collected during the 2017 RHIC run.

Neutrino-driven ejecta in core collapse supernovae (CCSNe) offer an interesting astrophysical scenario where lighter heavy elements between Sr and Ag can be synthesized. Previous studies emphasized the important role that ( α,n ) reactions play in the production of these elements, particularly in neutron-rich and alpha-rich environments. In this paper, we have investigated the sensitivity of elemental abundances to specific ( α,n ) reaction-rate uncertainties under different astrophysical conditions. Following a Monte Carlo nucleosynthesis study with over 36 representative astrophysical wind conditions, we have identified the most important reactions based on their impact on the final elemental abundances. Experimental studies of these reactions will reduce the nucleosynthesis uncertainties and make it possible to use observations to understand the origin of lighter heavy elements and the astrophysical conditions where they are formed.

Excitation energy spectra and absolute cross section angular distributions were measured for the 13C(18O,16O)15C two-neutron transfer reaction at 84 MeV incident energy. This reaction selectively populates two-neutron configurations in the states of the residual nucleus. Exact finite-range coupled reaction channel calculations are used to analyse the data. Two approaches are discussed: the extreme cluster and the newly introduced microscopic cluster. The latter makes use of spectroscopic amplitudes in the centre of mass reference frame, derived from shell-model calculations using the Moshinsky transformation brackets. The results describe well the experimental cross section and highlight cluster configurations in the involved wave functions.

The exact nature of the lowest K π = 2 + γ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ -bands have been traced past the usual back-bending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus 156Dy, using the 148Nd(12C,4n)156Dy reaction at 65 MeV, observing the resulting γ -ray transitions with the Gammasphere array. The even- and odd-spin members of the K π = 2 + γ γ -band are observed to 32+ and 31+ respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ -vibration built on the aligned yrast S-band are observed to spins 28+ and 27+. An even-spin positive-parity band, observed to spin 24+, is a candidate for an aligned S-band built on the seniority-zero configuration of the 0 + 2 state at 676 keV. The crossing of this band with the 0 + 2 band is at ℏω = 0.28(1) MeV and is consistent with the configuration of the 0 + 2 band not producing any blocking of the monopole pairing.

Background: Resonance scattering has been extensively used to study the structure of exotic, neutron-deficient nuclei. Extension of the resonance scattering technique to neutron-rich nuclei was suggested more than 20 years ago. This development is based on the isospin conservation law. In spite of broad field of the application, it has never gained a wide-spread acceptance. Purpose: To benchmark the experimental approach to study the structure of exotic neutron-rich nuclei through resonance scattering on a proton target. Method: The excitation function for p+8Li resonance scattering is measured using a thick target by recording coincidence between light and heavy recoils, populating T=3/2 isobaric analog states (IAS) in 9Be. Results: A good fit of the 8Li(p,p)8Li resonance elastic scattering excitation function was obtained using previously tentatively known 5/2- T=3/2 state at 18.65 MeV in 9Be and a new broad T=3/2 s-wave state - the 5/2+ at 18.5 MeV. These results fit the expected iso-mirror properties for the T=3/2 A=9 iso-quartet. Conclusions: Our analysis confirmed isospin as a good quantum number for the investigated highly excited T=3/2 states and demonstrated that studying the structure of neutron-rich exotic nuclei through IAS is a promising approach.