MATS and LaSpec: High-precision experiments using ion traps and lasers at FAIR
1 Departamento de Física Atómica Molecular y Nuclear, University of Granada, 18071 Granada, Spain
2 Max-Planck-Institute for Nuclear Physics, 69029 Heidelberg, Germany
3 Institut für Kernchemie, Johannes Gutenberg-Universität, 55099 Mainz, Germany
4 Variable Energy Cyclotron Centre, 1/AF, Kolkata, Bidhanagar, India
5 IFIC-CSIC University of Valencia, 46071 Valencia, Spain
6 CSNSM-IN2P3, CNRS, 91405 Orsay, France
7 Department of Physics, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland
8 GSI, Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany
9 CENBG/IN2P3, Bordeaux-Gradignan, France
10 Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
11 Michigan State University, NSCL, US-MI 48824-1321, East Lansing, USA
12 TRIUMF, CA-BC V6T 2A3, Vancouver, Canada
13 Pacific Northwest National Lab, PNNL, Richland, WA 99352, USA
14 CIEMAT, 28040 Madrid, Spain
15 UPC, 08034 Barcelona, Spain
16 CERN, 1211 Geneva 23, Switzerland
17 Raniganj Girls’ College, Raniganj, West Bengal, India
18 II. Institute of Physics, Justus-Liebig University, 35390 Gießen, Germany
19 Departamento de Física Aplicada, University of Huelva, 21071 Huelva, Spain
20 Department of Physics, Ludwig-Maximilians University München, 85748 Garching, Germany
21 St. Petersburg Nuclear Physics Institute, 188359 Gatchina and St. Petersburg State University, 198904 St. Petersburg, Russia
22 PNTPM, CP229, Université Libre de Bruxelles, 1050 Brussels, Belgium
23 Institute of Physics, Ernst-Moritz-Arndt University, 17487 Greifswald, Germany
24 SCFAB, Stockholm University, 10691 Stockholm, Sweden
25 Institute of Physics, Johannes Gutenberg-University, 55099 Mainz, Germany
26 Afd. Kern- en stralingsfysica, Katholieke Universiteit Leuven, 3001 Leuven, Belgium
27 IN2P3-CNRS, 91405 Orsay, France
28 Louisiana State University, US-LA 70803, Baton Rouge, USA
29 Institute of Theoretical Physics II, Friedrich-Alexander University, 91054 Erlangen, Germany
30 Lawrence Livermore National Laboratory, US-CA 94550-9234, Livermore, USA
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Nuclear ground state properties including mass, charge radii, spins and moments can be determined by applying atomic physics techniques such as Penning-trap based mass spectrometry and laser spectroscopy. The MATS and LaSpec setups at the low-energy beamline at FAIR will allow us to extend the knowledge of these properties further into the region far from stability.
The mass and its inherent connection with the nuclear binding energy is a fundamental property of a nuclide, a unique “fingerprint”. Thus, precise mass values are important for a variety of applications, ranging from nuclear-structure studies like the investigation of shell closures and the onset of deformation, tests of nuclear mass models and mass formulas, to tests of the weak interaction and of the Standard Model. The required relative accuracy ranges from 10−5 to below 10−8 for radionuclides, which most often have half-lives well below 1 s. Substantial progress in Penning trap mass spectrometry has made this method a prime choice for precision measurements on rare isotopes. The technique has the potential to provide high accuracy and sensitivity even for very short-lived nuclides. Furthermore, ion traps can be used for precision decay studies and offer advantages over existing methods.
With MATS (Precision Measurements of very short-lived nuclei using an A_dvanced Trapping System for highly-charged ions) at FAIR we aim to apply several techniques to very short-lived radionuclides: High-accuracy mass measurements, in-trap conversion electron and alpha spectroscopy, and trap-assisted spectroscopy. The experimental setup of MATS is a unique combination of an electron beam ion trap for charge breeding, ion traps for beam preparation, and a high-precision Penning trap system for mass measurements and decay studies. For the mass measurements, MATS offers both a high accuracy and a high sensitivity. A relative mass uncertainty of 10−9 can be reached by employing highly-charged ions and a non-destructive Fourier-Transform Ion-Cyclotron-Resonance (FT-ICR) detection technique on single stored ions. This accuracy limit is important for fundamental interaction tests, but also allows for the study of the fine structure of the nuclear mass surface with unprecedented accuracy, whenever required. The use of the FT-ICR technique provides true single ion sensitivity. This is essential to access isotopes that are produced with minimum rates which are very often the most interesting ones. Instead of pushing for highest accuracy, the high charge state of the ions can also be used to reduce the storage time of the ions, hence making measurements on even shorter-lived isotopes possible.
Decay studies in ion traps will become possible with MATS. Novel spectroscopic tools for in-trap high-resolution conversion-electron and charged-particle spectroscopy from carrier-free sources will be developed, aiming e.g. at the measurements of quadrupole moments and E0 strengths. With the possibility of both high-accuracy mass measurements of the shortest-lived isotopes and decay studies, the high sensitivity and accuracy potential of MATS is ideally suited for the study of very exotic nuclides that will only be produced at the FAIR facility.
Laser spectroscopy of radioactive isotopes and isomers is an efficient and model-independent approach for the determination of nuclear ground and isomeric state properties. Hyperfine structures and isotope shifts in electronic transitions exhibit readily accessible information on the nuclear spin, magnetic dipole and electric quadrupole moments as well as root-mean-square charge radii. The dependencies of the hyperfine splitting and isotope shift on the nuclear moments and mean square nuclear charge radii are well known and the theoretical framework for the extraction of nuclear parameters is well established. These extracted parameters provide fundamental information on the structure of nuclei at the limits of stability. Vital information on both bulk and valence nuclear properties are derived and an exceptional sensitivity to changes in nuclear deformation is achieved. Laser spectroscopy provides the only mechanism for such studies in exotic systems and uniquely facilitates these studies in a model-independent manner.
The accuracy of laser-spectroscopic-determined nuclear properties is very high. Requirements concerning production rates are moderate; collinear spectroscopy has been performed with production rates as few as 100 ions per second and laser-desorption resonance ionization mass spectroscopy (combined with β-delayed neutron detection) has been achieved with rates of only a few atoms per second.
This Technical Design Report describes a new Penning trap mass spectrometry setup as well as a number of complementary experimental devices for laser spectroscopy, which will provide a complete system with respect to the physics and isotopes that can be studied. Since MATS and LaSpec require high-quality low-energy beams, the two collaborations have a common beamline to stop the radioactive beam of in-flight produced isotopes and prepare them in a suitable way for transfer to the MATS and LaSpec setups, respectively.
© EDP Sciences, Springer-Verlag, 2010