The EXOGAM array

A new array, EXOGAM, is being designed by a collaboration involving France, the UK and other European partners, for use at the new SPIRAL facility at GANIL. The principal features of the above `ideal' arrangement are included. New segmented clover Ge detectors have been designed to be mounted in close geometry without sacrificing too much resolution through Doppler broadening. Each clover leaf measures $60\oslash \times 90$ mm³ and the crystals are strongly tapered. The clovers will be packed in an octagonal pattern at 90$^\circ$ to the beam, with up to 8 additional detectors at further 45$^\circ$ angles (see figures 4(b) and 5(a)). In this geometry, with the front faces 11.4 cm from the target, the total photopeak efficiency is 20% (at 1332 keV). The escape suppression shields are at the back, and adjacent clovers are in contact allowing add-back or further suppression of Compton scattered events. A less compact geometry, with the crystal faces at 14.7 cm has 12% efficiency. In the expanded geometry, additional suppression shields are added at the sides of the detectors and are protected by high-Z collimators. The different shields are shown in figure 5(b). Removing the four detectors in the forward hemisphere gives the configuration known as Exogam-12.

 

Figure: Provisional details of the EXOGAM array: (a) relative arrangement of the 16 segmented clover Ge detectors in space, and (b) shields and collimators for a single clover in EXOGAM [7].