Gamma ray detection with a 3 × 3 virtual Frisch grid array

A new design for a compact and rugged high-pressure xenon-filled ionization detector is being explored at Constellation Technology Corporation. The basic design approach is to use a detector geometry that eliminates the effect of the induced charge from uncollected ions without using any shielding mesh. The resulting device is called a virtual grid ionization chamber, and such devices can be constructed in a variety of different configurations. We have built several prototypes of slightly different design, and some have yielded a FWHM resolution of 2% at 0.662 MeV. These prototypes, being small, are best suited for use in hand held nuclear identifiers and Unmanned Aerial Vehicles (UAVs). However, this technology easily lends itself to being scaled up to large meter-sized panels that will provide high resolution, large area, and position sensitivity on a scale of 1 cm or better. We will discuss where we are with this “virtual Frisch grid” technology and where we are planning to go with it in the near future.