A resonator device comprises a plurality of transducers fitted and spatially aligned on the four prongs of two tuning forks, with vibrating masses, placed side-by-side with the four prongs arranged at 90.degree. angles one from the other in a clockwise or anticlockwise direction, the distance between the individual prongs, their dimensions, shapes and masses, producing mechanical vibrations and resonances at predetermined frequencies.

 
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> Intermediate density marker and a method using such a marker for radiographic examination

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