Nuclear Instruments and Methods in Physics Research A     Implanted silicon detector telescope New developments A
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Nuclear Instruments and Methods in Physics Research A Implanted silicon detector telescope New developments A

Musumarra F Amorini M Cabibbo G Cardella G DeGeronimo A DiPietro PG Fallica P Figuera M Papa G Pappalardo F Rizzo S Tudisco INFN Laboratorio Nazionale del Sud ia S So a 44 I95129 Catania Italy INFN Sezione di Catania Italy Uni ersita di Ca

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Nuclear Instruments and Methods in Physics Research A Implanted silicon detector telescope New developments A

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Nuclear Instruments and Methods in Physics Research A 409 (1998) 414 416 Implanted silicon detector telescope: New developments A. Musumarra , F. Amorini , M. Cabibbo , G. Cardella , G. DeGeronimo A. DiPietro , P.G. Fallica , P. Figuera , M. Papa , G. Pappalardo F. Rizzo , S. Tudisco INFN - Laboratorio Nazionale del Sud, ia S. So a 44, I-95129 Catania, Italy INFN, Sezione di Catania, Italy Uni ersita di Catania, Italy Politecnico di Milano and INFN sez. di Milano, Italy SGS-Thomson, Catania, Italy CEA DSM DAPNIA SPhN, Saclay, France Department of Physics and Astronomy, Uni

ersity of Edinburgh JCMB, King s Building, Scotland, UK Abstract As a result of a collaboration between SGS-Thomson and INFN, a Monolithic Silicon Detector Telescope with of 4 4mm with an ultra-thin stage (1 m) has been recently presented as a tool to identify low-energy heavy ions. The good performances obtained in the charge identication are anyway limited by the relatively small active area. We report on two new larger area telescopes. The rst one, a ve strip detector with each strip 3 4mm and a common stage, has given on-beam good results. The second one, a 20 20mm

active area, is under test and is limited by the high capacitance of the stage (40nF) requiring a suitable front-end electronics, presented in a dierent communication. 1998 Elsevier Science B.V. All rights reserved. 1. Introduction Charge discrimination for low-energy fragments is an important task for nowadays nuclear physics experiments where large acceptance detectors are in demand in order to detect and identify the par- ticles produced in the reactions. As an alternative to ionization chambers for low-energy thre- shold charge discrimination, implanted solid state telescopes [1]

are, for the rst time, industrially available as a result of a collaboration between Corresponding author. SGS-Thomson and INFN. Monolithic solid state detectors with an ultra-thin stage can now represent a good choice in terms of compactness and performances with a discrimination threshold of 300 400KeVA for fragments as carbon and nitrogen [1]. An intrinsic feature of such devices is the high capacitance limiting the surface of the rst detectors to 4 4mm : the corresponding capacitance of about 2 nF is at the limits of the standard pre-amplier coupling. To overcome

the problem, in such a way as to produce a larger surface detector, two directions have been explored: a new specic charge pre-amplier for high 0168-9002/98/$19.00 1998 Elsevier Science B.V. All rights reserved PII S0168-9002(98)00115-6
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capacitance to be coupled with a large surface- improved monolithic silicon detector (20 20mm and, as a further option, a segmented geometry for the stage (monolithic strip detector). 2. Large surface monolithic detector In the new generation of implanted detectors the whole fabrication process was improved and the implantation

energy of the buried boron P an- ode was increased to 1.25MeV. The cathode doping has been changed to arsenic and reach now a thickness of 300 nm as this minimizes shorts problems due to the metal penetration through the junction. Fig. 1a shows the updated device struc- ture. The rst lot of 20 20mm detectors exhibits a leakage current of about 100 nA and the capacitance, with 4V polarizing voltage, is 40nF (1 m active thickness). To solve the read-out prob- lem a new charge pre-amplier was developed at the Politecnico in Milan: we refer to the other contributions during the

Congress for further speci- cations [2]. The contemporary availability of the large surface detector and pre-amplier allowed us to perform a preliminary test with an 241 Am alpha source; in the chosen set-up an energy of about 200KeV is lost in the rst stage. Fig. 2 reports the matrix obtained and the and projec- tions. Apart from the new charge pre-amplier, stan- dard electronics was used as in Ref. [1] using the prescription of shaping the signal to 6 s in the 572 ORTEC amplier. Anyway, even with such large shaping the fast negative induction of de-

tector in the stage gives still some eects on the signal. During the test the detector was found noise sensitive and an appropriate set-up was necessary in order to assure the best performances: in particu- lar, connections between pre-amp and detector were maintained as short as possible (few cen- timeters). Resolution was also limited by a thermal noise of the implanted zone corresponding to a resistance of few ohm. We expect to have a full on- beam test in the next future in order to test charge discrimination performances and to better analyze the induction problem. Fig. 1. (a)

Structure (not in scale) of the new prototype of the implanted 2 2mm telescope. (b) View (not in scale) of the strip telescope. A. Musumarra et al. Nucl. Instr. and Meth. in Phys. Res. A 409 (1998) 414 416 415 IV. PARTICLE IDENTIFICATION
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Fig. 2. scatter plot obtained with alpha particles in air on the 20 20mm telescope. In the inserts and projec- tions are reported. 3. Strip monolithic detector The strip detector prototype, showed in Fig. 1b, with a total surface of 15 4mm , a common stage and the cathode divided into ve strips (3 4mm ), was tested by using the SMP

15-MV Tandem Accelerator of the Laboratorio Nazionale del Sud (INFN). The performed reaction was 27 Al 27 Al at -!" 145MeV and the detector was placed at -!" , 50cm far from the target. A standard electronic chain was used for each strip and the response was found to be similar to the 4mm prototype of Ref. [1]. Side eects giving cross-talk in the adjacent strip were measured up to 300 m from the edge of each strip looking at the signal from elastically scattered 27 Al ions. This eect can be drastically reduced with the use of guard rings and work is in progress to develop new

prototypes. The leakage for each strip was around 30nA with a polarization of 4 V. In Fig. 3 we pres- ent the matrix for a strip: a very good separ- ation is obtained for Quasi-Projectile Fragments and Fusion Evaporation Residue are also identied. Fig. 3. scatter plot obtained with one strip of the new strip-telescope. Charged fragments are well separated even near to the Bragg region up to charge 23. The line under the elastic peak is due to side eects not well suppressed. 4. Final remarks Two suitable geometries of the monolithic silicon detector have been presented;

preliminary tests show that both solutions work with dierent constraints in terms of associated electronics and physical requirements. Large surface appears to be the best solution in experiments demanding high solid angle coverage in spite of a dedicated front- end electronics. On the other hand, the strip de- tector is best adapted to measurements where a good angular resolution is required and can be read with standard charge pre-ampliers, so that the problem of a high number of electronic chains can be overcome by the existing integrated or hy- brid electronics. References

[1] G. Cardella et al., Nucl. Instr. and Meth. A 378 (1996) 262. [2] G. De Geronimo et al., these Proceedings (7th Pisa Meeting on Advanced Detectors, La Biodola, Isola dElba, Italy, 1997) Nucl. Instr. and Meth. A 409 (1998) 307. 416 A. Musumarra et al. Nucl. Instr. and Meth. in Phys. Res. A 409 (1998) 414 416