Session L13: Nuclear Structure II

Beta Decay of Neutron-Rich Nuclei Near 60Ca

Isotopes in the vicinity of the neutron dripline near ⁶⁰Ca are valuable for providing information on the dripline and the neutron-rich region near magic number Z = 20. These nuclei were produced at the National Superconducting Cyclotron Laboratory via fragmentation of a 140MeV/u ⁸²Se beam impinging on a ⁹Be target. The isotopes were separated in the A1900 and identified, event-by-event, by measuring energy loss and time-of-flight. They were then implanted in a double-sided silicon strip detector, with high and low gain outputs, to allow for investigation of the β-decay half-lives. Two high-purity germanium detectors were used to search for excited states in the daughter nuclei. Preliminary results will be reported.   

Modernizing NuDat Using the Latest Computing Technologies to Facilitate Nuclear Physics Research

   The National Nuclear Data Center (NNDC) at Brookhaven National Laboratory (BNL) has developed and maintained NuDat, a web application where users can explore several databases containing nuclear structure, nuclear decay, and neutron-induced nuclear reaction information. NuDat is the primary web application used to query and visualize meticulously evaluated recommended values derived from all published experimental nuclear structure and decay data contained within the Evaluated Nuclear Structure Data File (ENSDF). NuDat was first developed over 15 years ago and now there are over 4 million queries to NuDat each year for research, education, and a wide range of applications.

   The modernized NuDat 3.0 contains responsive nuclear data visualizations to support user needs and uniquely visualize the vast amounts of data that ENSDF has to offer. Users can seamlessly interact with over 3,300 nuclides with intuitive pan and zoom gestures. NuDat 3.0 has a full range of features to support exploring nuclear data such as supplementary plots that can automatically sync to the current view of the interactive chart of nuclides.

   Beyond the interactive chart of nuclides, NuDat offers a full suite of web applications to search and visualize nuclear data.The Advanced Cross-Variable Plot provides users with an interface to create various plots by selecting axis variables from a multitude of observable properties. These feature rich and dynamic visualizations are both highly interactive and customizable. Fully interactive level and decay schemes for relevant nuclei have been implemented.

   NuDat 3 will continue to improve based on feedback from the community with a focus on developing novel visualization tools to provide users with an intuitive interface to the nuclear data within ENSDF. The ubiquitous demand for meticulously evaluated nuclear data emphasizes the need for modernizing NuDat using the latest computing technologies, in order to provide an enhanced user experience.   

First Results using Clarion 2

To further test the FSU shell model interaction\footnote{R. S. Lubna \textit{et al.}, Phys. Rev. Research \textbf{2}, 043342 (2020)} we have observed gamma rays from high spin states in $^{32}$P using the $^{18}$O($^{16}$O,pn) reaction at E$_{lab}$ = 30 MeV at the FSU Fox Laboratory. From the preliminary analysis, most gamma ray transitions from the previous work proposed by Chakrabarti \textit{et al.}\footnote{R. Chakrabarti \textit{et al.}. Phys. Rev. C \textbf{84}, 054325 (2011)} can be confirmed. Polarizations of some observed transitions have been deduced from the use of Compton scattering in the Clover spectrometers. Also for the first time, results from the new Clarion 2 gamma array will be reported to further investigate this nucleus. The level scheme agrees very well with calculations of the FSU interaction which illustrate the hierarchy of multiparticle-hole excitations in generating higher spin.   

Modernizing ENSDF - Design, Conversion, and Web Access

The Evaluated Nuclear Structure Data File (ENSDF) format was originally created for punch cards, and still retains its design to this day. The 80-column text files in ENSDF store decades of nuclear structure and decay research in a format which is difficult to parse and challenging to expand. Fortunately, developments in database technology make it possible to re-design ENSDF for the needs of future research. The National Nuclear Data Center (NNDC) is creating a multi-project pipeline that starts with new dataset formats written in JavaScript Object Notation (JSON). As these formats are produced, original ENSDF datasets are also being converted to preserve existing data. The JSON data files are then stored in a CouchDB database which can accommodate more flexible and understandable designs. Lastly, a web request API is being developed to ensure that ENSDF datasets remain publicly accessible. By addressing each of these steps in individual projects, the NNDC aims to maintain ENSDF as a valuable source of data for decades to come.   

Scaling approach to nuclear structure in high-energy heavy-ion collisions

In high-energy heavy-ion collisions, the energy density profile of the produced quark-gluon plasma and its space-time dynamics are sensitive to the shape and radial profiles of the nuclei, described by the collective nuclear structure parameters including quadrupole deformation $\beta_2$, octupole deformation $\beta_3$, radius $R_0$ and surface diffuseness $a$. Using a transport model simulation as a proxy for hydrodynamics, we find a general scaling relation between these parameters and a large class of experimental observables such as elliptic flow $v_2$, triangular flow $v_3$ and particle multiplicity distribution $p(N_\mathrm{ch})$ In particular, we show that the ratio of these observables between two isobar collision systems depends only on the differences of these parameters. Using this scaling relation, we show how the nuclear structure parameters of $^{96}$Ru and $^{96}$Zr conspire to produce the non-monotonic centrality dependence of ratios of $v_2$, $v_3$ and $p(N_\mathrm{ch})$ between $^{96}$Ru+$^{96}$Ru and $^{96}$Zr+$^{96}$Zr collisions, in agreement with measurements by the STAR Collaboration. We investigate how these scaling relations depend on the transport properties such as $\eta/s$ and found they are insensitive to these final-state effects. Furthermore, we extend this study to include the systems with similar mass number, and rather robust corrections to these scaling relations are found. This scaling approach towards heavy-ion observables demonstrates that isobar collisions is a precision tool to probe the shape and radial structures, including the neutron skin, of the atomic nuclei across energy scales.   

Global investigation of differential mean-square charge radii in covariant density functional theory.

A systematic global investigation of differential charge radii has been performed within the CDFT

framework for the first time. Theoretical results obtained with conventional covariant energy density

functionals and separable pairing interaction are compared with experimental differential

charge radii in the regions of the nuclear chart in which available experimental data crosses neutron

shell closures at N = 28; 50; 82 and 126. The analysis of absolute differential radii of different isotopic

chains and their relative properties indicate clearly that such properties are reasonably well described

in model calculations in the cases when the mean-field approximation is justified. However, while

the observed clusterization of differential charge radii of different isotopic chains is well described

above the N = 50 and N = 126 shell closures.

It is shown that the kinks in the charge radii at neutron shell closures are due to the underlying single-particle structure and due to weakening or collapse of pairing at

these closures. The regions of the nuclear chart in which the correlations beyond mean-field are

expected to have an impact on charge radii are indicated; the analysis shows that the assignment

of a calculated excited prolate minimum to the experimental ground state allows to understand

the trends of the evolution of di erential charge radii with neutron number in many cases of shape

coexistence even at the mean- field level. It is usually assumed that pairing is a dominant contributor

to odd-even staggering (OES) in charge radii. Our analysis paints a more complicated picture. It

suggests a new mechanism in which the fragmentation of the single-particle content of the ground

state in odd-mass nuclei due to particle-vibration coupling provides a signi cant contribution to

OES in charge radii.   

Electromagnetic Transition Rates in 28Mg

Neutron rich Mg isotopes far from stability belong to the island of inversion, a region where the single particle energy state description of the shell model breaks down and the predicted configuration of the nuclear states becomes inverted. Nuclei in this region also exhibit collective behaviour in which multiple particle interactions play a significant role in nuclear wavefunctions and transitions. This can be observed through electromagnetic transition strength measurements.

In-beam reaction experiments performed at TRIUMF, Canada's particle accelerator centre, allow for precision measurements of nuclei far from stability. Using TIGRESS in conjunction with the TIGRESS Integrated Plunger for charged particle detection, electromagnetic transition rates can be measured to probe nuclear wavefunctions and perform tests of theoretical models using the well-understood electromagnetic interactions.

In this talk, I will discuss an experiment performed using TIGRESS and the TIGRESS Integrated Plunger to measure the lifetime of the first excited state in 28Mg. This experiment utilized both the Doppler Shift Attenuation Method and the Recoil Distance Method, which exploit the Doppler shift of gamma rays emitted in flight, in order to be sensitive to both short- and long-lived states in the nucleus. The current state of data analysis and the impacts on nuclear physics will be discussed.