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Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy of radionuclides

Periodic Reporting for period 2 - MIRACLS (Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy of radionuclides)

Reporting period: 2018-07-01 to 2019-12-31

The MIRACLS project aims to develop and employ a novel method to perform high-resolution laser spectroscopy of exotic, short-lived radionuclides which are currently out of reach for conventional techniques. To this end, the novel approach of the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS) is determined to enhance the sensitivity of classical collinear laser spectroscopy by a factor of 20-600. It is based on an electrostatic ion beam trap (EIBT) or also called multi reflection time of flight (MR-ToF) device in which the radioactive ions bounce back and forth between two electrostatic mirrors. This scheme allows extended observation times and hence higher experimental sensitivity. In order to preserve the high resolution of conventional collinear laser spectroscopy, MIRACLS' MR-ToF device will be operated at a beam energy of 30 keV compared to a few keV in contemporary MR-ToF instruments.

The MIRACLS technique currently under development at ISOLDE/CERN will open the path to probe exotic radionuclides located in currently (in terms of laser spectroscopy) uncharted territory of the nuclear landscape. Among others, these measurements will reveal the nuclear charge radii of short-lived radionuclides which are crucial benchmarks for modern nuclear structure theory. Indeed, advances in nuclear theory have recently lead to improved theoretical descriptions of nuclear charge radii along Calcium, Tin, or Cadmium isotopic chains. Data to be harvested by MIRACLS will next probe results of these theoretical calculations for even more exotic nuclides. Due to the higher asymmetry in their neutron-to-proton ratio, these nuclides far away from stability are expected to expose otherwise subtile features of the nuclear force and hence represent challenging benchmarks for our understanding of atomic nuclei.
After the setup of the required continuous-wave laser system, a proof-of-principle experiment to demonstrate the technical feasibility and scientific potential of the novel MIRACLS approach has been assembled. First photons of laser-excited ions of stable magnesium isotopes, confined in an MR-ToF device, were detected in August 2018. This success represent a major advance in the development of MIRACLS. Since then, the technique was further advanced and systematic studies of collinear laser spectroscopy in an MR-ToF device were performed.

In parallel, an advanced MIRACLS apparatus operating at higher ion beam energy was designed. In addition to the 30-keV MR-ToF device, it will also host a next-generation Paul trap for optimal preparation of the radioactive ion beam. The design of this apparatus is based on extensive simulations of the ion trajectories in the MR-ToF device and Paul trap as well as on the practical lessons learned in the previously described proof-of-principle experiment.
Given the successful demonstration of the novel MIRACLS approach in a proof-of-principle experiment, the project is on track to perform high-resolution laser spectroscopy of exotic, short-lived radionuclides once ISOLDE is back online after the end of the long CERN shutdown in 2021. The demonstrated increased in experimental sensitivity will allow MIRACLS to pursue high-resolution laser spectroscopic studies of exotic nuclides currently out of reach by existing techniques.