Beta Decay at the Limits of Nuclear Stability: Integrating Ab Initio Calculations and Kinematically Complete Measurements

Project Overview

New theoretical and experimental tools have been developed to fully characterize the rich set of both beta-delayed particle-emission phenomena and to elucidate the nature of the Standard Model of Particle Physics (SM) by searching for exotic currents in the weak interaction through measurements of correlation observables. This has been accomplished through the development of the BeTrap, a linear Paul ion trap that extends our charged-particle and recoil-ion detection techniques and can measure the emergence of all charged decay particles resulting from beta-delayed particle emission, including the low-energy nuclear recoil, from the ion trap without attenuation, enabling the first full kinematic reconstruction of these decays. In parallel, coupling our ab initio methodologies for the description of continuum dynamics and beta-decay between bound nuclear states we obtained, for the first time, a quantum many-body description of beta-delayed particle emission that implements our best understanding of the nuclear and electroweak forces, and can simultaneously describe both the bound and continuum nuclear states at play. Additionally, a successful Lawrence Livermore National Laboratory–Soreq Applied Research Accelerator Facility collaboration (project scope increase FY19) has been initiated, culminating in a precision measurement of the beta-decay branching ratio of neon-23 (²³Ne) to the first excited state of sodium-23 (²³Na), permitting a redetermination of the beta-neutrino angular correlation coefficient in this nuclear system. This new collaboration opens the possibility to further perform experiments to test the SM or utilize the intense proton and neutron beams to study beta-delayed particle emission processes.

Mission Impact

This effort is critical to keep Livermore at the forefront of low-energy nuclear science over the next decade and has positioned the Nuclear and Particle Physics and Nuclear Data and Theory Groups for leadership roles in nuclear-structure studies at the Facility for Rare Isotope Beams (FRIB). With this effort we were able to: 1) develop an ion trap, the BeTrap, which has been designed to measure beta-delayed charged particle emission and can be systematically extended to characterize decay properties of medium-mass and heavy unstable nuclei crucial to stellar evolution and the synthesis of the elements and is expected to play a key role in the FRIB Decay Station stopped-beam program; and 2) spearhead the development of a more extensive approach that combines our theoretical framework with emerging ab initio methods for medium-mass and heavy nuclei, thus enabling the accurate description of beta-delayed particle emission from isotopes produced at FRIB. This research advances Livermore's nuclear, chemical, and isotopic sciences core competency.

Publications, Presentations, and Patents

Boucher, B. 2020. "Geant4 simulations of beta-delayed particle emission of 11Be in a linear Paul trap." MSc Thesis. Golden, Colorado. Colorado School of Mines.

Gallant, A. 2019. "A new trap to measure beta-delayed particle emission." TITAN Collaboration Meeting, Vancouver. LLNL-PRES-773343

Gallant, A., et al. 2020. "Direct measurement of the beta-delayed proton branch in ¹¹Be using a new ion trap at TITAN for charged particle spectroscopy." TRIUMF Experimental Evaluation Committee Letter of Intent. LLNL-PROP-798903