Population inversion of nuclear states by a Penning trap mass spectrometer

¹ CERN, Physics Department - 1211 Genève 23, Switzerland
² GSI - Planckstraße 1, 64291 Darmstadt, Germany
³ NSCL, Michigan State University - East Lansing, MI 48824-1321, USA
⁴ CSNSM-IN2P3-CNRS - 91405 Orsay-Campus, France
⁵ Institute of Physics, Ernst-Moritz-Arndt-University - 17487 Greifswald, Germany

Received: 7 April 2004
Accepted: 2 June 2004

Abstract

According to the energy-mass equivalence, E=mc², excited long-lived nuclear states, so-called isomers, are distinguished from the ground state by their additional mass. The ultra-high accuracy provided by Penning traps now allows to weigh nuclear excitation energies. With the on-line Penning trap mass spectrometer ISOLTRAP, we have developed a mass-separation procedure of sufficient resolving power to isolate particles of a selected isomeric state from an ensemble delivered from the radioactive beam facility ISOLDE at CERN, first demonstrated for . The resulting unique form of ion ensembles opens up a large variety of new nuclear-physics experiments. Mass excesses of for the 1⁺ ground state and for the 6^- isomeric state have been determined.