Conveners
Nuclear Structure I: NS 1
- Gordon Ball (TRIUMF)
Nuclear Structure I: NS 2
- Sofia Quaglioni (LLNL)
Nuclear Structure I: NS 3
- Paul Garret (University of Guelph, Canada)
Nuclear Structure I: NS 5
- Jack Henderson (University of Surrey)
Nuclear Structure I: NS 6
- Silvia M. Lenzi (University of Padua and INFN)
Nuclear Structure I: NS 7
- Steven Pain (ORNL)
Nuclear Structure I: NS 8
- Wolfram KORTEN
The experimental search for an isolated four-neutron system has been a long standing quest in nuclear physics. With only a few indications for its existence the tetraneutron remains an elusive nuclear system. In the recent experiment performed at RIKEN Nishina Center a resonance-like structure near 4n threshold was observed for the first time using quasi-free knockout of alpha particles from...
Even though beta-delayed proton emission is a phenomenon that typically occurs for neutron-deficient nuclei, the energy window for this process is open also in a few light, neutron-rich isotopes. Particularly interesting in this respect is 11Be, which is also a one-neutron halo nucleus. Several channels for beta-delayed particle emission from this isotope are open, including the proton branch,...
We present recent results on the gamma decay of a peculiar near-threshold state in 11B, expected to be located in the continuum just above the proton-decay threshold. The relevance of such a state is due to the observation of the rare beta-delayed proton emission process in the neutron-rich 11Be nucleus, with an unexpectedly high rate, at odds with the narrow energy window available for this...
Dipole strengths of direct and cascade transitions to GDR energies in medium and heavy atomic mass nuclei are investigated in a theoretical approach based on EDF theory and extended by multiphonon degrees QRPA [1]. Recent developments of the method, including a reaction theory [2,3], have been applied in spectroscopic studies of two-phonon states [4], pygmy and giant resonances [1-5], thus...
In nuclei near the $N=20$ island of inversion, the non-central tensor components of the nuclear interaction drive the preferential population of $pf$-shell orbitals over the $sd$-shell orbitals predicted by the spherical shell model. High precision excited state lifetime measurements in nuclei across the Mg isotopic chain provide a means by which this evolution of neutron shells can be studied...
The conventional magic number N=20 has been shown to break down in the region of neutron-rich nuclei centered around $^{32}$Mg (Z=12, N=20) known as the N=20 Island of Inversion. At the same time, a new magic number at N=16 has been suggested to emerge around $^{24}$O (Z=8, N=16). The neutron-rich nucleus $^{25}$Ne (Z=10, N=15) lies in this zone of rapid change in nuclear structure....
The semi-magic $^{120}_{50}$Sn$_{70}$ lies in the neutron mid-shell among the other stable Sn isotopes, where $2p-2h$ intruder configurations built on excited 0$^+$ states have been recently observed. However, the transition rates from the $0^+_3$ state in $^{120}$Sn are not well-known because its lifetime only has a lower limit of 6 ps, which prevents a firm assignment or exclusion of the...
A search for new isotopes near the neutron dripline was conducted for fluorine, neon and sodium at RIKEN RIBF [1], in which isotopes were produced by projectile fragmentation of an intense 48Ca beam at 345 MeV/nucleon, and separated and identified in flight using the large-acceptance two-stage separator BigRIPS [2,3]. The 48Ca beam intensity was as high as ~540 pnA. In the experiment we...
In the area known as the “island of inversion,” neutron-rich nuclei around N=20 exhibit substantial admixtures of intruder configurations in their ground states, thus leading to the breakdown of the N=20 major shell gap. Central to this island of inversion is the nucleus 32Mg, which has been the subject of study for several decades and serves as a critical benchmark for nuclear models and our...
In recent years, fusion-evaporation reactions have increasingly been used to study neutron-rich nuclides near the $N=20$ 'island of inversion' [1 - 3]. In this region, the evolution of the $N=20$ shell gap is indicated by the energies of negative parity states which primarily arise due to single neutron excitation to the higher lying $fp$ orbitals. These negative parity states often have...
The focus of this work is neutron-rich Fe and Mn isotopes with N~40, which lie within an Island of Inversion approximately centered at 64Cr. Here, a quenching of the N=40 sub-shell gap allows multi-particle multi-hole excitations and deformation to develop in the ground-state configurations of nuclei in the region. Limited spectroscopic information has been collected so far in the...
Systematic investigations of nuclear reactions are crucial for advancing the field of nuclear physics. So far, traditional methods, like charged particle probes, $\beta$-decay and heavy-ion fusion evaporation reactions, have been employed to explore the phase space of shell models. Using fast-neutron probes would further expand the horizon of possibilities. Despite their use for cross-section...
Since advent of the RIBF, the NaI(Tl) based scintillation array DALI2+ has been the workhorse for in-beam gamma-ray spectroscopy experiments with fast beams. Due to its modest energy resolution, caused by large opening angles and intrinsic energy resolution of NaI(Tl) scintillators, its suitable mostly for spectroscopy at the isospin limit. Accordingly, the "Shell Evolution and Search for...
The nuclear structure of doubly magic nuclei, such as 100Sn and its neighboring isotopes, has attracted significant attention from both experimental and theoretical perspectives. This interest stems from the unique insights it offers for testing the nuclear shell model and its relevance to the astrophysical rapid-proton capture process [1].
The Cd isotopic chain plays a crucial role in...
Background: Over the past two decades high energy-resolution inelastic proton scattering studies were used to gain an understanding of the origin of fine structure observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector giant dipole resonance (IVGDR). Recently, the isoscalar giant monopole resonance (ISGMR) in $^{58}$Ni, $^{90}$Zr, $^{120}$Sn and $^{208}$Pb was studied...
New results on the strongly deformed proton-rich $A\approx 115 \div 130$ nuclei obtained from recent experiments performed using high-efficiency gamma-ray arrays and ancillary detectors will be presented. Shape coexistence in Cs nuclei and the extent of octupole correlations in Xe and Ba nuclei will be discussed. The experimental results will be compared with different theoretical models...
The experimental B(E2) values in light even-even Sn isotopes are found to be enhanced compared to theory, a discrepancy which has eluded a satisfactory solution for over a decade. For further examination, supplementary information such as spectroscopic quadrupole moments ($Q_s$) are needed.
A safe-energy Coulomb excitation of $^{110}$Sn was conducted at HIE-ISOLDE, CERN. The $^{110}$Sn beam...
It is well known that nucleons are arranged in specific shells resulting in greater stability, analogous to the electron shells in the atom and that this shell structure was expected to be very robust in the whole nuclear chart. However, with new experimental techniques and progress in the production of radioactive ion beams during the last two decays, we are now aware that the shell structure...
The nuclear two-photon or double-gamma (2γ) decay is a second-order electromagnetic decay process whereby a nucleus in an excited state emits two gamma rays simultaneously. It proceeds via the virtual excitation of higher-lying intermediate states. Compared to first-order decay pathways, such as single photon emission or internal conversion, the two-photon decay rate is very small. Ideal cases...
The natural time scales of nuclear physics are such that, in the course of a collision at energies near the barrier, both structure and dynamic effects are vitally important to the resulting reaction outcomes. While this complicates theoretical descriptions of heavy-ion reactions, it opens an avenue to study difficult-to-probe phenomena like neutron skins and nucleonic equilibration across a...
Octupole correlations in nuclei near 𝑁 = 𝑍 occur between nucleons when both protons and neutrons occupy the same orbitals. This phenomenon is prominent in light Te (𝑍 = 52), I (𝑍 = 53), and Xe (𝑍=54) nuclei, especially around 𝑁 ∼ 56 and 𝑍 ∼ 56. The Fermi surface for neutrons and protons lies close to orbitals from the $d_{5∕2}$ and $h_{11∕2}$ subshells, leading to enhanced octupole...
The low-lying structure of 13Be has remained an enigma for decades. Despite numerous experimental and theoretical studies, inconsistencies remain. Being both unbound and one neutron away from 14Be, the heaviest bound beryllium nucleus, 13Be is difficult to study through simple reactions with weak radioactive-ion beams or more complex reactions with stable-ion beams. Data from a study of 13Be...
The evolution of the shell structure observed in exotic nuclei has led to a change of paradigm in our understanding of the nuclear force. Extensive knowledge of the modification of shell gaps in the oxygen chain has been gathered over the past decades. With two-protons below, the carbon isotopes show exotic properties and are a good testing ground for understanding new aspects of nuclear...
The commissioning of transfer reaction measurements in inverse kinematics in the SOLARIS solenoid with the Active Target Time Projection Chamber (AT-TPC) was successfully completed in the summer of 2021 at the NSCL. The goal of this experiment was to demonstrate the possibility of performing transfer reaction measurements at low beam intensities (between 100 Hz - 1 kHz) using the high...
Unlike any other physical system, the atomic nucleus represents a unique dual quantum many-body system. Its constituents, protons and neutrons, are assumed to be identical, except for their electric charge. They can be seen as two representations of the nucleon, with isospin components t_z = ±1/2 for neutrons and protons, respectively. Under the assumption of charge independence of the strong...
Studying the nuclei along and near the N=Z line is the best way to find answers to some fundamental questions in nuclear structure, such as charge-dependence of the nuclear interaction or the role of the proton-neutron pairing. Despite our deep understanding of the electromagnetic interaction, the differences in the binding energies in mirror nuclei cannot be reproduced theoretically, thus...
Nuclear pairing, i.e., the tendency of nucleons to form pairs, has important consequences to the physics of heavy nuclei and compact stars. While the pairing found in nuclei typically happens between identical nucleons and in spin-singlet states, the exotic spin-triplet and mixed-spin pairing phases have also been hypothesized. In this talk, I will present new investigations confirming the...
Recently, high-energy nuclear collisions have been proposed as a powerful tool to image the global structure of heavy atomic nuclei, such as their shapes and radial profiles. We present the first quantitative demonstration of this method by extracting the quadruple deformation $\beta_2$ and triaxiality $\gamma$ for $^{238}$U nuclei, known for its large prolate shape. We achieve this by...
