The UltraLo-1800 is a windowless, ultra low background alpha particle counter designed to measure the alpha particle emissivity of solid materials. The system employs the patented technique of electronic background suppression, which drives achievable background rates to 0.0001 alphas/cm2/hr and below. This is a factor of 50 or more better than can be achieved by the conventional proportional counter systems that are currently available. With the UltraLo-1800, it becomes feasible to measure samples having emissivities in the 0.001 to 0.0005 alpha/cm2/hr range in fewer than 10 hours, and to measure emissivities below 0.0005 alpha/cm2/hr in fewer than 100 hours.