Microdosimetry: Measured probabilities for energy deposited by mesons in one-micron sites in silicon

Probabilities of ionizing events and probability distributions for energy deposited by positive and negative pi mesons and positive mu mesons have been measured in one-micron equivalent sites in silicon. A new low-noise silicon proportional counter was developed to measure complete distributions beginning at a few electron-volts per micrometer. The data show that 140-MeV/c pions when compared with 80-MeV muons are more likely to initiate processes with thresholds greater than about 50 MeV/kg/m2. These results support our earlier hypothesis that, at lower altitudes, pions are more likely to induce errors in memory chips than muons. It is proposed that error rates from pions at lower elevations may be comparable in number to those from neutrons.