Abstract A modified design of a jumping spark counter capable of counting the damage trails produced by alpha particles emitted in the decay of radon (released from uranium ore bodies) has been developed. The device consists of two electrodes made up of aluminised mylar and thin metallic foil respectively. The modified system is convenient and yields better plateau than that obtained by using the conventional systems. Efforts have been made in optimising the device for attaining one to one correspondence between the microscopically observed hole density and the track counts in the system. Experience shows that the counting system can be effectively used for the evaluation of uranium ore samples.