A search for an exotic natural radioactivity of lead nuclei, using nuclear
emulsion sheets as detector, is described. We discuss the experimental set-up
of a test performed at the Gran Sasso National Laboratory (Italy), the event
simulation, data analysis and preliminary results.Comment: 5 pages, 2 EPS figures. Talk given at the 11th ICATPP Conference
on Astroparticle, Particle, Space Physics, Detectors and Medical Physics
Applications, Como (Italy), 5-9 October 200