DETECTION OF ALPHA-PARTICLES BY SURFACE E LECTRIC CHARGES

The trajectory of one or a few alpha particles can be visualized by co llecting on a dielectric the charges released in the gas by ionisation . The charge quantity obtained, without multiplication, is small and d ifficult to extract from the background noise. This background noise i s, in particular, due to the residual charges or polarization near the surface of the dielectric. This residual surface charges have been si gnificantly reduced by balancing them with charges created by a beam o f alpha particles. Then, the reading of charges due to one particle ca n be performed with an electrometric measuring setup using a rotating head.