A search for anomalously heavy isotopes of lithium using laser-based mass spectrometry

A laser-based method called SIRIS is being used to search for anomalously heavy isotopes of normal elements, which may result from the attachment of new stable elementary particles of high mass to ordinary nuclei. The basic components of the method are sputter atomization of a solid sample, resonance ionization and time-of-flight mass spectrometry. Preliminary results are reported for the case of lithium. No interesting candidates in the mass range 380-1000 amu are found at a tentative concentration limit of (3-6)x10-12 per nucleon. Further improvements in the method should lead to a sensitivity of 10-15 without enrichment