Ultra-Low Emissivity Alpha-Particle Detection

New alpha counters make accurate measurements of low emissivity samples possible. Modeling results set lower limits for measurements at sea level of silicon substrates to about
$0.3\ \alpha/{\hbox {khr-cm}}^{2}$
. Our measurements demonstrate the effect of cosmic ray shielding on the measured alpha-particle emissivity. A few atoms of radon contamination can cause elevated emissivities many days after exposure.