The MIRACLS project at ISOLDE/CERN develops and employs 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) enhances 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 (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, a dedicated MIRACLS' MR-ToF device is designed to operate at a beam energy of 30 keV compared to a few kiloelectronvolts in contemporary MR-ToF instruments.
The MIRACLS technique has opened a path to probe exotic radionuclides located in currently (in terms of laser spectroscopy) uncharted territory of the nuclear landscape. Among others, these measurements 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 led to improved theoretical descriptions of nuclear charge radii along Magnesium, Calcium, Tin, or Cadmium isotopic chains. Due to the higher asymmetry in their neutron-to-proton ratio, radionuclides very far away from stability but accessible by MIRACLS expose subtile features of the nuclear force and hence represent challenging benchmarks for modern nuclear theory and generally our understanding of atomic nuclei.
While MIRACLS was developed for fluorescence-based collinear laser spectroscopy, its high potential for other applications was also recognised. Perhaps most interestingly, we have used the novel methods to precisely measure electron affinities, i.e. the released energy when an electron is attached to a neutral atom. The electron affinity of an element is an important property in chemistry (eg. reactivity) as well as atomic theory (eg. many body correlations).
