Nuclear Physics

Lund University


A rather recent approach to isotope-selective spectroscopy of radioactive nuclei is to first prepare a well defined nuclear quantum state by means of a precision mass selection in a Penning trap. Subsequently, the nuclei are transferred into a decay spectroscopy station. Both at the GSI laboratory and the University of Jyväskylä, it turned out that the TASISpec detector system can easily be placed behind SHIPTRAP or JYFLTRAP, respectively. The same will be true for the new Lundium decay station put together with the large 2015 grant from the Knut and Alice Wallenberg foundation. In the FAIR-NUSTAR future, Lundium may be places behind MATS or an MR-ToF/gas-catcher system.

Schematically, the combination of Penning trap and decay station is illustrated in the figure below. The development of the method can be best accessed via the Lund PhD thesis of Christian Lorenz.

A set of ions, pre-selected in recoil velocity by SHIP, enters the stopping gas cell at the entrance of SHIPTRAP, which is shown on the left hand side. The next step involves the tuning of the extraction and purification of the singly- or doubly-charged ions of the isotope of spectroscopic interest. The ions extracted from the gas cell are cooled and accumulated in the radiofrequency quadrupole buncher before being transferred to the purification (Penning) trap. For an unambiguous isotope identification a mass measurement is performed in the second trap, the so-called measurement trap, of SHIPTRAP. Finally, the MCP detector at the exit of SHIPTRAP is removed from the beam axis, and the nuclei of a given mass are allowed entering the TASISpec decay station through a focussing tube. In conjunction with the acceleration, deflection, and focussing elements of SHIPTRAP, an optimum near 100% transmission has been achieved in commissioning experiments, proving the principle for comprehensive decay radiation measurements of a given nuclear quantum state.

The picture below provides an overview of how the combination of SHIPTRAP and TASISpec looks in reality.

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Ch. Lorenz
Selektion av atomkärnors kvanttillstånd och deras sönderfall
Fysikaktuellt 1, 10 (2019).

Ch. Lorenz, L.G. Sarmiento, D. Rudolph et al.,
β Decay of 127Cd and Excited States in 127In
Phys. Rev. C99, 044310 (2019).

Ch. Lorenz, L.G. Sarmiento, D. Rudolph et al.,
Quantum-state-selective decay spectroscopy of 213Ra
Phys. Rev. C96, 034315 (2017).

L.G. Sarmiento and D. Rudolph
Nuclear Spectroscopy with Geant4: Proton and Neutron Emission & Radioactivity
AIP Conf. Proc. 1753, 070007 (2016).

L.-L. Andersson et al.
A Study of the Possibilities and Limitations of the TRAPSPEC Setup,
GSI Scientific Report, NUSTAR-SHE-09, 213 (2011).

D. Rudolph et al.
TRAPSPEC - Towards Isotope-Selected Decay Spectroscopy,
GSI Scientific Report, NUSTAR-SHE-08, 177 (2009).