Hamburg 2009 – scientific programme
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MS: Fachverband Massenspektrometrie
MS 6: Laser-Resonanzionsation und REMPI
MS 6.1: Talk
Tuesday, March 3, 2009, 16:00–16:15, VMP 8 R05
RIMS of thorium isotopes - Towards a laser spectroscopic identification of the low-lying 7eV isomer of 229Th — Juha Äystö1, Iain Moore1, Tina Gottwald2, Thomas Kessler1, Sebastian Raeder2, •Volker Sonnenschein1, and Klaus Wendt2 — 1University of Jyväskylä, Finland — 2Johannes Gutenberg Universität, Mainz
High resolution gamma-spectroscopic experiments indicate a isomeric state 229mTh, I=3/2+ lying very closely above the ground state 229gTh, I=5/2+ with an excitation energy of only about 3.5-7 eV. These measurements used a differencing technique of the gamma-ray decay paths, while, however, direct observation of the decay of the isomer or its decay to the ground state was unsuccessful so far.
An alternative approach to gamma-spectroscopy would be identification of the isomer through a measurement of its corresponding hyperfine structure relative to the structure of the ground state. As a first step to achieve a highly sensitive detection of the isomer, an efficient laser ionization scheme of thorium was developed using stable 232Th. A solid state titanium sapphire (Ti:Sa) laser system, including a wide-tunable grating-based Ti:Sa laser, was used to analyze a large energy region above the ionization potential in the search for transitions to autoionizing states.
As a next step, a suitable efficient scheme will be used for a study of the hyperfine structure of the 229Th ground state. This investigation will utilize a seeded Ti:Sa laser for high-resolution resonance ionization spectroscopy measurements.