Fast proportional chamber with freon-14 and isobutane mixture

The multiwire proportional chamber with a diameter of 12 cm is shown to be able to operate at very high counting rates of 0.5x106 particles/s per wire (or 5x107 particles/s per 10 cm2 of the chamber area). This performance was achieved with gas mixtures of CF4 and isobutane i-C4H10 (80%-20%) at atmospheric pressure with a small anode-cathode distance of 4 mm. The equivalent noise charge of the preamplifier-shaping system is ∼ electrons 103. Such a low equivalent noise charge allows to operate at gas gains of about 103 and to reduce space charge effects