Position-Sensitive Si(Li) Transmission Detectors for the EXL-Experiments at GSI-Darmstadt

1. EXL-1 EXL-2 Position-Sensitive Si(Li) Transmission Detectors for the EXL-Experiments at GSI-Darmstadt D. Protić, T. Krings, S. Niessen, Forschungszentrum Jülich, Institut für Kernphysik (IKP), Jülich, Germany P. Egelhof, Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany E. C. Pollacco, CEA Saclay, France for the EXL collaboration Abstract MUST2-Si(Li) setup and modifications for the EXL-Si(Li) setup A large target-recoil detector will be constructed for the future EXL-experiments (EXotic nuclei studied in Light-ion induced reactions) at the NESR storage ring of the future FAIR project at GSI-Darmstadt [1]. As a part of the recoil detector, position-sensitive Si(Li) transmission detectors (5 to 9 mm thick) are intended for construction of DE-E charged-particle telescopes. Si(Li) detectors of transmission type has been an important aspect concerning the total-energy measurement for target recoils transversing the silicon DE-E telescopes and stopped in inorganic scintillators placed behind the telescopes. Two ~7 mm thick Si(Li) transmission detectors equipped with 8 pads on the implanted p+-contact have being prepared for the test measurements at ESR (GSI-Darmstadt). To relieve the efforts for the first experiments a telescope configuration and position-sensitive structure very similar to that of the MUST2 experiment (SACLAY, ORSAY and GANIL) will be applied [2], but with UHV-capable components. Results of the test measurements in the laboratory are presented. MUST2-Si(Li) setup (n-contact) to replace to replace MACOR-blocks HV-board (ceramic) VESPEL-blocks MUST2-Si(Li) setup to replace by UHV-capable parts Schematic view of the Si(Li) transmission detector (p+-contact) 8 position elements (pads) are separated by ~60 mm wide and ~15 mm deep plasma etched (SF6-plasma) grooves Al-bonded wires to replace ceramic boards ~200 mm wide connecting strips Ø 102 mm Ø 92 mm 3 to 5 mm wide guard-ring PCBs out of FR4 ~ 6.5 mm boron-implanted p+-contact covered with evaporated aluminum layer (thickness: < 1mm) Si(Li) detector EXL-1 in the UHV-compatible housing 48 mm thinned Li-diffused n-contact covered with evaporated aluminum layer (effective thickness [3]: < 5 mm) 54 mm ceramic board MACOR blocks (to contact the 8 pads) Li-compensated region (intrinsic zone) Li-diffused contact Si(Li) detector prototype for test measurements p+-contact (not yet thinned) (structured with 8 pads) Specifications: Momentary status: HV ceramic board EXL-1 EXL-2 • transmission type Si(Li) detector Results of the first laboratory measurements 6.5 mm thick 6.4 mm thick • ~ 6.5 mm thick • 8 pads on the boron-implanted contact • the same structure as for the Si(Li) detectors for the MUST2-setup p+-contact is still without position-sentive structure 298 K 283 K 275 K operating bias: +700 V p+-contact is structured • thin Li-diffused contact • reverse current (total) 20 mA 6.0 mA 3.1 mA • effective thickness below 5 mm • without position-sensitive structure Li-diffused contact has to be thinned ~ 3 mm „thick“ Li-diffused contact • reverse current per pad 110-200 nA 30-60 nA 15-31 nA • resistance pad - neighbourhood > 1 MW > 1 MW > 1 MW • operating bias:  700 V • energy resolution [FWHM] per pad for 5.8 MeV a-particles 26-41 keV 25-30 keV 23-25 keV • energy resolution [FWHM] for 5.8 MeV a-particles: < 50 keV • energy resolution [FWHM] per pad for pulser line 15-29 keV 13-20 keV 11-13 keV see: Results of the first laboratory measurements T = 273 K • reverse current / pad: < 250 nA • resistance pad - neighbourhood: > 1 MW effective thickness of the Li-diffused contact [3] determined with the help of a-particles • housing / frame: test measurements (energy resolution, reverse current, inter pad resistance) are being performed the photolithography for performing the position-sensitive structure on the p+-contact is started up • design is identical to the MUST2-design • all components have to be UHV-compatible @ 273 K @ 298 K 600 V 4.2 mm 5.0 mm 700 V 2.3 mm 3.4 mm operating bias 800 V 1.5 mm 2.2 mm Conclusion and outlook 1000 V 0.6 mm 0.8 mm • the manufacture of the two detectors will be completed within the next weeks. The Li-diffused contact of the Si(Li) detector EXL-1 will be thinned and the p+-contact of the Si(Li) detector EXL-2 will receive the position-sensitive structure. • UHV-capable components of the detector holder have been already finished • test measurements in UHV environment will be performed inside the ESR-ring at GSI-Darmstadt References [1] www.gsi.de [2] E. C. Pollacco et al., to be published in Nucl. Instr. Meth. [3] D. Protić and T. Krings, “Development of transmission Si(Li) detectors”, IEEE Trans. Nucl. Sci., vol. 50, pp. 1008-1012, August 2003 Contact: d.protic@fz-juelich.de, t.krings@fz-juelich.de, p.egelhof@gsi.de IEEE Nuclear Science Symposium, 29.10. – 4.11.2006, San Diego, USA