An Encapsulated Silicon Junction Alpha-Particle Detector

The construction of a silicon diffused junction alpha detector in a form which allows complete encapsulation and protection of the junction edge, and which preserves a good geometry is described. The unit is inherently shielded from electrical pickup, and is shielded from ambient light by a thin metallic film over the sensitive surface. A modified form of the same encapsulation has been used for large area units of 2 cm2 suitable for contamination monitoring. Measurements of energy resolution and other characteristics are reported for units of sensitive area 5 mm2, 20 mm2 and 200 mm2.