Periodic Reporting for period 1 - PRESOBEN (PREcision Studies with Optically pumped Beams of Exotic Nuclei)
Reporting period: 2022-09-01 to 2025-02-28
Neutrons are fascinating particles and are important for nuclear structure, tests of the standard model of particle physics, or properties of neutron stars. Unfortunately, they are electrically neutral, so learning about their distribution in nuclei, especially far from stability, is difficult. However, they possess a magnetic moment, which contributes to –and sometimes dominates– the distribution of nuclear magnetization. This project aims to address the challenging question of the distribution of magnetisation and neutrons in unstable nuclei. We will use a novel, high-accuracy experimental approach, combining radiation-detected Nuclear Magnetic Resonance with rf-laser double spectroscopy on optically-pumped short-lived nuclei. The project builds on recent achievements, allowing to determine magnetic moments of unstable nuclei up to ppm accuracy. We will combine this approach with accurate measurements of the hyperfine structure using the laser-rf double-resonance. The signals will be detected efficiently using anisotropy in beta or gamma decay, thanks to spin polarisation via optical pumping. This will lead to an accurate determination of a ‘hyperfine anomaly’, a small effect on atomic hyperfine structure due to the distribution of nuclear magnetisation. A close collaboration with atomic and nuclear theorists will allow to determine the magnetisation and neutron distribution in many nuclei: light neutron-halo beryllium-11, proposed halos in neutron-rich neon, sodium, magnesium, potassium and calcium, and heavy radon, francium, and radium isotopes, interesting for studies of atomic parity violation (APV) and electric dipole moments. The project will take place at the ISOLDE facility at CERN. We will also work closely with quantum-chemistry, atomic- and nuclear-physics theorists, who will use our data to improve their approaches. This will open new perspectives for nuclear structure studies, determination of neutron-star properties, or APV studies. It will also allow tests of atomic and nuclear calculations.
In the first 2 years of the project, we have made substantial progress in all aspects of the project.
Concerning very light halo nuclei, such as beryllium-11, we have defended the scientific proposal to measure precisely its magnetic moment. We have also finalised the design and assembly of the 1st energy-resolving beta detector, and we were preparing for the 1st online experimen on 11Be. Our nuclear-theory collaborators are meanwhile working on calculating the effect of finite distribution of magnetisation in very light nuclei.
In the medium-mass nuclei, a doctoral thesis was defended on the measurement of magnetic moment of potassium-47 and determination of its hyperfine anomaly. our nuclear-theory colleagues have determined the parameters needed for a theoretical value of the hyperfine anomaly of 47K, thus allowing to interpret our experimental result. A common publication to a high-impact journal was close to finalisation.
Concerning the new technique of laser-rf double resonance spectroscopy on short-lived nuclei, we have designed and tested the 1st prototype and we are working on the final design of an rf transmission line. We have successfully defended a proposal to study neutron-rich potassium isotopes to investigate the possible neutron skin that theory predicts nearby.
We have also performed 2 experiments with a new end station allowing to record beta, gamma, and neutron decay from polarised nuclei, with the aim to test the sensitivity of the technique to decay asymmetry of radiation other than beta.
Concerning very light halo nuclei, such as beryllium-11, we have defended the scientific proposal to measure precisely its magnetic moment. We have also finalised the design and assembly of the 1st energy-resolving beta detector, and we were preparing for the 1st online experimen on 11Be. Our nuclear-theory collaborators are meanwhile working on calculating the effect of finite distribution of magnetisation in very light nuclei.
In the medium-mass nuclei, a doctoral thesis was defended on the measurement of magnetic moment of potassium-47 and determination of its hyperfine anomaly. our nuclear-theory colleagues have determined the parameters needed for a theoretical value of the hyperfine anomaly of 47K, thus allowing to interpret our experimental result. A common publication to a high-impact journal was close to finalisation.
Concerning the new technique of laser-rf double resonance spectroscopy on short-lived nuclei, we have designed and tested the 1st prototype and we are working on the final design of an rf transmission line. We have successfully defended a proposal to study neutron-rich potassium isotopes to investigate the possible neutron skin that theory predicts nearby.
We have also performed 2 experiments with a new end station allowing to record beta, gamma, and neutron decay from polarised nuclei, with the aim to test the sensitivity of the technique to decay asymmetry of radiation other than beta.
The PhD thesis from our group, as well as an upcoming article, include the 1st measurement of the hyperfine anomaly in a short-lived nucleus at a 1e-3 level.
Our experimental result is combined with 1st calculations of the hyperfine anomaly using state-of-the-art nuclear model and atomic calculations. Furthermore, nuclear theory colleagues have included contributions from 2-body-currents.
We developed a very novel technique: decay spectroscopy on laser-polarised mid-mass unstable nuclei, which has been used on beams lighter than Mg on only 1 setup in the world, at TRIUMF in Canada. We have employed it to potassium isotopes.
Our experimental result is combined with 1st calculations of the hyperfine anomaly using state-of-the-art nuclear model and atomic calculations. Furthermore, nuclear theory colleagues have included contributions from 2-body-currents.
We developed a very novel technique: decay spectroscopy on laser-polarised mid-mass unstable nuclei, which has been used on beams lighter than Mg on only 1 setup in the world, at TRIUMF in Canada. We have employed it to potassium isotopes.