Resonant laser ionization and spectroscopy are widely used techniques at radioactive ion beam facilities to produce pure beams of exotic nuclei and measure the shape, size, spin and electromagnetic ...multipole moments of these nuclei. However, in such measurements it is difficult to combine a high efficiency with a high spectral resolution. Here we demonstrate the on-line application of atomic laser ionization spectroscopy in a supersonic gas jet, a technique suited for high-precision studies of the ground- and isomeric-state properties of nuclei located at the extremes of stability. The technique is characterized in a measurement on actinium isotopes around the N=126 neutron shell closure. A significant improvement in the spectral resolution by more than one order of magnitude is achieved in these experiments without loss in efficiency.
For the analysis of low-statistics counting experiments, a traditional nonlinear least squares minimization routine may not always provide correct parameter and uncertainty estimates due to the ...assumptions inherent in the algorithm(s). In response to this, a user-friendly Python package (SATLAS) was written to provide an easy interface between the data and a variety of minimization algorithms which are suited for analyzinglow, as well as high, statistics data. The advantage of this package is that it allows the user to define their own model function and then compare different minimization routines to determine the optimal parameter values and their respective (correlated) errors. Experimental validation of the different approaches in the package is done through analysis of hyperfine structure data of 203Fr gathered by the CRIS experiment at ISOLDE, CERN.
Source code: https://github.com/woutergins/satlas/
Documentation: https://woutergins.github.io/satlas/
Program Title: SATLAS
Program Files doi:http://dx.doi.org/10.17632/3hr8f5nkhb.1
Licensing provisions: MIT
Programming language: Python
External routines/libraries: NumPy, SciPy, LMFIT, Pandas, NumDiffTools
Nature of problem: Fitting data from a counting experiment to extract parameter information.
Solution method: Supply a modular library with fitting routines using pre-implemented goodness-of-fit statistics for counting data under different circumstances.
The changes in the mean-square charge radius (relative to 209Bi), magnetic dipole, and electric quadrupole moments of 187, 188, 189, 191Bi were measured using the in-source resonance-ionization ...spectroscopy technique at ISOLDE (CERN). A large staggering in radii was found in 187, 188, 189Big, manifested by a sharp radius increase for the ground state of 188Bi relative to the neighboring 187, 189Big. A large isomer shift was also observed for 188Bim. Both effects happen at the same neutron number, N = 105 , where the shape staggering and a similar isomer shift were observed in the mercury isotopes. Experimental results are reproduced by mean-field calculations where the ground or isomeric states were identified by the blocked quasiparticle configuration compatible with the observed spin, parity, and magnetic moment.
Many experiments with pulsed ion beams benefit from or even require ion bunches with both small temporal width as well as small energy spread. To achieve optimal ion-beam preparation, a buffer-gas ...filled cryogenic Paul trap is being developed in the context of the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS). There, ion bunches of short-lived radionuclides are trapped in a Multi-Reflection Time-of-Flight (MR-ToF) device. Thus, the ions can be repeatedly probed by a laser beam compared to only once in conventional, single-passage collinear laser spectroscopy. To fulfill MIRACLS’ opposing requirements of a small temporal ion-bunch width and small energy spread, a buffer-gas filled cryogenic Paul trap is envisioned. Ion-optical simulations confirm the advantages of cryogenic temperatures and the linear scaling of the beam emittance as a function of the buffer-gas temperature. Beyond MIRACLS, high-quality ion beams from a cryogenic Paul trap will be beneficial for other precision experiments at radioactive ion beam facilities.
The Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS) seeks to extend the reach of high-resolution collinear laser spectroscopy (CLS) to more exotic radionuclides. In this ...novel technique, ion bunches of short-lived radioisotopes are trapped between two electrostatic mirrors of a Multi-Reflection Time-of-Flight (MR-ToF) device at 30-keV kinetic energy. The same ion bunch can be probed by a spectroscopy laser for thousands of times compared to a single probing in the traditional CLS measurement scheme. Thus, the experimental sensitivity is increased by more than one to two orders of magnitude. Extensive simulations are presented, demonstrating the feasibility of high-resolution collinear laser spectroscopy (CLS) in the newly envisioned MR-ToF apparatus operating at ion energies of 30 keV. Once the mechanical design and operational parameters are optimized for the requirements of CLS, the spectral line is neither significantly broadened nor distorted by the combination of CLS and MR-ToF operation. According to the simulations, the storage efficiency and the ion–laser overlap are suitable for laser excitation of the majority of the trapped ions. In summary, >90% injection and storage efficiency, >75% ion–laser overlap and a line width approaching the natural line width of the transition of interest are reached in the simulation.
The changes in mean-squared charge radii of neutron-deficient gold nuclei have been determined using the in-source, resonance-ionization laser spectroscopy technique, at the ISOLDE facility (CERN). ...From these new data, nuclear deformations are inferred, revealing a competition between deformed and spherical configurations. The isotopes ^{180,181,182}Au are observed to possess well-deformed ground states and, when moving to lighter masses, a sudden transition to near-spherical shapes is seen in the extremely neutron-deficient nuclides, ^{176,177,179}Au. A case of shape coexistence and shape staggering is identified in ^{178}Au which has a ground and isomeric state with different deformations. These new data reveal a pattern in ground-state deformation unique to the gold isotopes, whereby, when moving from the heavy to light masses, a plateau of well-deformed isotopes exists around the neutron midshell, flanked by near-spherical shapes in the heavier and lighter isotopes-a trend hitherto unseen elsewhere in the nuclear chart. The experimental charge radii are compared to those from Hartree-Fock-Bogoliubov calculations using the D1M Gogny interaction and configuration mixing between states of different deformation. The calculations are constrained by the known spins, parities, and magnetic moments of the ground states in gold nuclei and show a good agreement with the experimental results.
Collinear laser spectroscopy (CLS) has been performed in a multi-reflection time-of-flight (MR-ToF) device operated in single-pass mode, i.e., without confining the ions in the ion trap. While our ...Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS) aims to increase the CLS sensitivity by storing ions in the MR-ToF device, the present work characterises conventional single-passage CLS as a preparatory step for the upcoming comparison with MIRACLS’ multi-pass mode. To this end, the isotope shift in the 3s2S1/2→3p2P3/2 transition (D2 line) between ions of the magnesium isotopes 24Mg and 26Mg has been measured under varying experimental conditions. Our result agrees with the precise literature value. Associated studies of systematic uncertainties demonstrate a measurement accuracy of better than 20 MHz in this new apparatus. This value will serve as the reference for analogous studies to be performed in the MIRACLS approach in which ions are trapped in the MR-ToF device for thousands of revolutions and probed by the spectroscopy laser during each passage.
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