Electronic background rejection in a new ultra-low background alpha-particle counter

Low background alpha-particle (α) counting is required in the semiconductor industry, where α’s produce single event errors. Industry road maps call for measuring α emissivities at 0.0005 α/cm2/h, while current commercial counter backgrounds are 0.005 α/cm2/h, a factor of 10 too high. This paper shows that by designing an ionization chamber so that ionization tracks collected from the sample have long risetimes while those collected from the anode have short risetimes, signal risetime analysis can distinguish α emanation location within the counter. Coupled with a guard electrode to reject tracks emitted from the counter sidewalls, the method can achieve backgrounds approaching 0.0001 α/cm2/h, a factor of 20 lower.