A -ray detector with high photopeak efficiency, granularity and large solid angle is the MINIBALL. Six clusters with seven 6-fold segmented Ge-detectors (in total 252 segments) constitute a cube that surrounds 65% of the target solid angle.

Individual Ge detector(bottom and side view)

HVone Ge-segment

The Gamma DetectorThe Gamma Detector

• Each individually aluminium encapsulated Ge-detector is 6-fold segmented to ensure the necessary granularity. Pulse shape analysis improves the energy resolution and the primary -ray interaction position determination.

• A cluster consist of 7 Ge-detectors (without BGO anti-compton shielding) configured as shown below. To each cluster a cryostat is connected which cools the Ge-crystals (=> less noise). • MINIBALL data

Granularity = 252 segments in 4 = 65%ph > 20% for 1.3 MeV -rays

ph > 5% for 11.7 MeV -rays

Multiplicity M < 15

Energy resolution = 2 - 3 keVLocalization = 1 cm for 1.3 MeV -raysCounting rate < 10 kcs-1 per Ge-detector

• Six clusters make up a cube array with an inner radius > 9 cm. For a nucleus velocity v/c ~0.05 the energy resolutionE equals

7 keV at E = 1.3 MeV for the most

problematic observation angle of 90°. The cluster arrangement gives a high geometric modularity and flexibility.

Cluster

Cube array with cryostats