Session H03: Advances in Nuclear Structure II

Covariant density functional theory studies of exotic nuclei

Covariant density functional theory (CDFT) is one of the modern theoretical tools for the description of finite nuclei and neutron stars. Its performance is defined by underlying covariant energy density functionals (CEDFs) with a few parameters adjusted to the properties of finite nuclei and nuclear matter. To give an overview of CDFT, I will highlight some of its basic features and main challenges. Following that, a potential effort to improve the performance of CEDFs will be addressed [1]. A new anchor-based optimization method has been proposed and has shown significant improvements in the description of physical observables [2].

A discussion of modern applications of CDFT models in the description of exotic nuclei will follow. A systematic investigation of the ground state and fission properties of even-even actinides and superheavy nuclei with proton numbers $Z = 90-120$ located between the two-proton and two-neutron drip lines has been performed with proper assessment of systematic theoretical uncertainties [3,4]. These results provide necessary theoretical input for the modeling of the nuclear astrophysical r-process taking place in the mergers of neutron stars. The final part of my presentation will deal with the extension of the nuclear landscape to hyperheavy $(Z > 126)$ nuclei. The nuclear landscape is substantially increased by the transition from ellipsoid-like nuclear shapes to toroidal ones in the region of hyperheavy nuclei [5].   

Fermi’s favorite figure – the history of the pseudopotential concept in atomic and neutron physics

In the early 1930’s Fermi wrote two papers in which he introduced the concepts of “scattering length” and “pseudopotential”. Since that time, these terms have become universally associated with low energy scattering phenomena. Even though the two papers are very different - one in atomic physics, the other in neutron physics - a simple figure underlies both. The figure appears many times in Fermi’s work. We review how the two papers came about, and briefly discuss modern developments of the work that Fermi initiated with these two remarkable papers.

    

University of Kentucky Accelerator Laboratory Neutron Scattering Cross Section Measurements Incorporating Recent Laboratory Upgrades

The University of Kentucky Accelerator Laboratory (UKAL) houses a 7-MV Van de Graaff accelerator capable of delivering a pulsed proton or deuteron beam that is impinged on gas (tritium or deuterium) targets to deliver roughly  monoenergetic neutrons per second. Using time-of-flight techniques coupled with neutron and gamma-ray detection capabilities, UKAL supports a nuclear data program aimed at updating and affirming the accuracy of neutron elastic and inelastic differential cross sections for a wide variety of isotopes of interest for nuclear energy applications. A brief overview of UKAL, its capabilities, and updates to its data acquisition system and analysis pipeline will be presented along with recent results on elastic and inelastic neutron scattering cross sections at incident neutron energies from 0.5 to 8.0 MeV.  

    

Cross section measurements for the 110Cd(n, γ) and 111Cd(n, γ) reactions

In nuclear physics, the cross-section for a specific interaction between a projectile particle and a target nucleus is the main nuclear data quantity which reflects the likelihood of that specific interaction occurring. Specifically, the neutron absorption cross-section of a specific nuclide expresses how likely a projectile neutron might be absorbed by and fused to the target nuclide. This quantity is distinctive for a specific target nuclide, and it varies with the speed (kinetic energy) of the projectile neutron. There are many important applications for neutron capture cross section information. In particular, for the cadmium nuclei, neutron capture cross sections are important for non-destructive assay techniques for nuclear safeguards as well as the astrophysical r- and s-processes. In this work, we report on efforts to determine the neutron absorption cross section of ¹¹⁰Cd and ¹¹¹Cd, using ¹¹⁰Cd (n, γ) ¹¹¹Cd and ¹¹¹Cd (n, γ)¹¹²Cd reactions, respectively, in the range of 1 eV – 300 KeV neutron energies. The experiment was performed at the Los Alamos Neutron Science Center (LANSCE) using the Detector for Advanced Neutron Capture Experiments (DANCE), which utilizes 160 BaF₂ crystal detectors spanning almost a 4π geometry. In the presentation, the setup up of the experiment, the data acquisition, and the technique of data analysis to determine the neutron absorption cross sections for ¹¹⁰Cd and ¹¹¹Cd will be discussed along with a presentation of current progress towards this ultimate goal.

Key words: neutron absorption cross section, nuclear data, DANCE.

    

The Search for Mirror Neutrons in 2020 Experiment at SNS

As a candidate for dark matter, the world of mirror matter is one with which we cannot interact directly; at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratories, our group has attempted to understand mirror matter by observing neutron-to-mirror neutron oscillations. The transformations from neutrons to mirror neutrons and back can act as a portal between matter and mirror matter. I was tasked with analyzing the data from the experiment performed at the SNS in November of 2020. This experiment consisted of a beam of cold neutrons that would be exposed to a magnetic field where in the center was a cadmium absorber. Neutrons in this magnetic field were supposed to be converted to mirror neutrons that can pass the absorber without interaction; then, while they are still in the magnetic field, they regenerate back into ordinary neutrons that are ultimately detected. My main goal is to characterize the intensity of the initial neutron beam, which is used to calculate the probability of the transformations occurring. I analyzed the data primarily using python along with C++ for further optimization. Six intensity calibration data files were analyzed, and among these six, various numbers of polycarbonate plates were used to attenuate the initial neutron beam. After defining a region of interest where regenerated neutrons have hit the detector along with a region of background resulting from scattered neutrons, I employed statistical methods to remove the background from under the beam intensity peak. Plotting the intensity of the peak of the data from these six files against the respective number of plates used in each run could be utilized to determining the intensity of the initial beam through fitting. With a determined intensity, the probability of quantum mechanical processes behind the oscillations into mirror particles can be further understood.