Center for Exotic Nuclear Studies

ASGARD (Array of Super clover Gamma-Ray Detectors)

1. Physics motivation

• Magic number
• Shell evolution
• Shape evolution
• Shape coexistence
• Island of inversion
• Seniority

Figure 1 “Pear” shaped nucleus [Nature, 497, 199 (2013)]

Figure 2 New magic number “34” in 54Ca [Nature 502, 207 (2013)]

Figure 3 Shape coexistence in 40Mg [Nature 587, 66 (2020)]

Figure 4 Nuclear shell evolution [J. Phys. G 43, 024009 (2016)]

2. ASGARD specification

Figure 5 ASGARD conceptual design with 16 units of clover detectors

• Comprised of 16 units of the 4-fold 32-segmented clover detector
• 8 units installed in the middle ring (90°), each 4 units installed in forward (135°) and backward (45°) rings
• 11 cm from the center to the detector face in the most compact geometry
• Each detector can move forward and backward.
• Each detector can hold Compton suppressors

3. Details of clover detector

Figure 6 Single unit of clover detector

• 4 crystals encapsuled, each segmented by 8 electrodes
• Capability of pulse shape analysis
• 60-mm diameter, 90-mm length size crystal
• Less than 2.35 keV in FWHM @ 1.33 MeV
• More than 38% relative efficiency (25-cm source location)
• Require LN2 cooling for operation

4. Functionality

Figure 7 Simulated detection efficiency of ASGARD

Figure 8 Expected energy resolution for in-beam spectroscopy