Characteristics of segmented super clover detector in close geometry decay measurements

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY 4.0 https://creativecommons.org/licenses/by/4.0/ Characteristics of segmented super clover detector in close geometry decay measurements © Authors, 2001 Published version Rahkila, Panu; Grahn, Tuomas; Eskola, Kari; Gerl, J.; Greenlees, Paul; Jones, P.; Joss, D. T.; Julin, Rauno; Juutinen, Sakari; Kankaanpää, Harri; Keenan, A.; Kettunen, Heikki; Kojouharov, I.; Kuusiniemi, Pasi; Leino, Matti; Melarangi, A.; Moore, C. J.; Muikku, Maarit; Nieminen, Päivi; Page, R. D.; Scholey, C.; Uusitalo, Juha Rahkila, P., Grahn, T., Eskola, K., Gerl, J., Greenlees, P., Jones, P., Joss, D. T., Julin, R., Juutinen, S., Kankaanpää, H., Keenan, A., Kettunen, H., Kojouharov, I., Kuusiniemi, P., Leino, M., Melarangi, A., Moore, C. J., Muikku, M., Nieminen, P., . . . Uusitalo, J. (2001). Characteristics of segmented super clover detector in close geometry decay measurements. Acta Physica Polonica B, 32(3), 773. http://www.actaphys.uj.edu.pl/fulltext?series=Reg&vol=32&page=773 2001 Vol. 32 (2001) ACTA PHYSICA POLONICA B No 3 CHARACTERISTICS OF SEGMENTED SUPER CLOVER DETECTOR IN CLOSE GEOMETRY DECAY MEASUREMENTS  P. Rahkila a , T. Grahn a , K. Eskola b , J. Gerl  , P.T. Greenlees a P. Jones a , D.T. Joss d , R. Julin a , S. Juutinen a , H. Kankaanpää a A. Keenan a , H. Kettunen a , I. Kojouharov  , P. Kuusiniemi a M. Leino a , A. Melarangi e , C.J. Moore e , M. Muikku a y P. Nieminen a , R.D. Page e , C. Sholey e , and J. Uusitalo a a Department of Physis, University of Jyväskylä P.O.Box 35 (Y5), FIN-40351 Jyväskylä, Finland b Department of Physis, University of Helsinki, Helsinki, Finland  Gesellshaft für Shwerionenforshung, Darmstadt, Germany d Sho ol of Sienes, Staordshire University, Stoke-on-Trent, UK e Oliver Lo dge Lab oratory, University of Liverpo ol, Liverp o ol, UK (Reeived January 24, 2001) Charateristis of the segmented Super Clover germanium detetor resp onse in lose geometries have b een studied. Results obtained with lo alising hit pattern reognition are ompared with results from add-bak and individual rystal analysis. The detetor has been used at the fo al plane of a gas lled reoil separator to detet isomeri gamma-rays from the nulei pro dued in the 150 Sm( 42 Ca,4n) 188 Pb reation. Coinidene data from the detetor was analysed and the level sheme b elow the 1.2  s isomeri state in 188 Pb ould b e dedued. PACS numbers: 29.30.Kv, 29.30.Gx, 29.85.+, 23.20.g 1. Intro dution Comp osite germanium detetors typially have a large ative volume [1, 2℄, thus they are very eient and suitable for o-b eam gamma-ray sp e- trosopy in lose geometries. Segmentation of omp osite detetors [35℄ an b e advantageous also in o-b eam sp etrosopy. Position sensitivity of the  Presented at the XXXV Zakopane Shool of Physis Trends in Nulear Physis, Zakopane, Poland, Septemb er 513, 2000. y Present address: CLRC, Daresbury Lab oratory, Daresbury, UK. (773) 774 P. Rahkila et al. segmented omp osite detetor allows the lo alisation of deteted gammarays within the detetor to b e determined. It is also p ossible to separate oinident gamma-rays. The GSI Sup er Clover detetor [6, 7℄ onsists of four large n -typ e HPGe rystals, eah of 6 m diameter and 14 m length b efore shaping. The rystals are eletrially segmented into four quadrants on their outer ontat (gure 1(a)). The resulting 16 separate sub-volumes are oupled into nine signals (gure 1(b)). The four enter ontats have go o d energy and timing resolution while the outer segmented ontats with lower signal quality are used for lo alisation. The detetor was surrounded by an 8 element suppression shield (gure 1(b)). 0000000 0000000 0000000 1111111 1111111 1111111 00 00 00 00 00 00 00 00 00 00 00 00 11 11 11 11 11 11 11 11 11 11 11 11 000000 000000 000000 111111 111111 111111 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 0000000 0000000 1111111 1111111 000000 000000 111111 111111 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 a) b) C1 C4 C2 C3 P1 P2 P2 P3 P4 P5 P5 P6 P4 P5 P5 P6 P7 P8 P8 P9 Fig. 1. (a) Illustration of the Sup er Clover rystals. (b) Shemati drawing of the 9-fold segmentation sheme and the BGO shield. The enter ontats (C1-C4) have goo d energy and time resolution while the p osition signals (P1-P9) are used to lo alise the gamma-rays. The elements of the BGO shield are indiated using hathing. 2. Analysis mo des and detetor harateristis Data from the detetor were analysed using three dierent metho ds: (i) in total add-bak mo de, (ii) as four individual rystals and (iii) using a hit pattern reognition algorithm develop ed for segmented lover detetors. In the algorithm the 16-fold segment hit pattern is reovered using b oth rystal and p osition signals. The pattern is searhed for isolated hits of a single or adjaent double or triple segments. The energy and time of the Charateristis of Segmented Super Clover Detetor in ::: 775 inident gamma-rays are then alulated from the energy and time signals of the inner ontats overlapping the pattern found. No heks of rystal or p osition energies are done, whih makes the metho d simple and indep endent of the quality of the p osition signals but at the same time some sensitivity is lost. Charateristis of the detetor were measured with radioative soures plaed on the axis of the detetor 2.5 m from the detetor fae. Absolute eienies dedued from the 60 Co data show that the individual rystal mo de is the most eient of the three at this distane, having a photop eak eieny of approximately 5.5% at 1332 keV. For b oth total add-bak and the hit pattern reognition, the add-bak fator drops b elow 1.0 from typial values of 1.5 and 1.2 measured at the standard 25 m soure-detetor distane. In the ase of total add-bak this reets the large probability of oinidene summing as the solid angle subtended by the whole detetor is nearly 30% at 2.5 m. Hit pattern reognition is less aeted by the oiidene summing but the oupling of the segments makes the reovery of some sattering paths (for example C1P5-C2P4) imp ossible using the simple hit pattern reognition alone. In the latest segmented lover detetors with 16-fold unoupled segmentation the p erformane of the hit pattern reognition algorithm should b e b etter. The BGO shield was used in three dierent ongurations in whih a rystal was veto ed with (all) eight, four or two losest elements. Whole shield suppression was found to give optimum p erformane. 3. Isomer sp etrosopy of 188 Pb The detetor was subsequently plaed at the fo al plane of the RITU [8℄ gas lled reoil separator. The reoiling nulei pro dued in the 150 Sm( 42 Ca,4 n ) 188 Pb reation were separated from b eam partiles and ssion pro duts by the separator and implanted into a p osition sensitive silion strip detetor (PSSD). Delayed    events deteted in the lover detetor plaed at 2.5 m from the PSSD were sorted into matries using individual rystal analysis mo de. Transitions de-exiting the 1.2  s isomeri state at an exitation energy of 2576 keV in 188 Pb were identied using an additional ondition that the gamma-rays must have b een deteted within 3  s after the reoil implantation (gure 2). The data are in agreement with those prop osed by Heese et al. [9℄ and Draoulis et al. [10℄ and show that the detetor an b e used to detet oinident events in suh exp eriments. 776 P. Rahkila et al. 0 100 200 300 400 500 600 700 800 900 1000 Energy [keV] 0 20 40 60 80 100 Counts / keV = Transitions de−exciting the 8−, 1.2µs isomer in 188Pb Pb X−rays Fig. 2. Energy sp etrum of oinident gamma rays observed 3  s after the reoil implantation and gated by the 723, 340 and 370 keV transitions. This work has b een supp orted by the Aademy of Finland under the Finnish Centre of Exellene Programme 2000-2005 (Pro jet No. 44875, Nulear and Condened Matter Programme at JYFL) and by the Europ ean Union Fifth Framework Programme proving Human Potential  Aess to Researh Infrastruture. The Sup er Clover detetor is the prop erty of GSI, Germany. REFERENCES [1℄ P.J. Nolan et al. , Annu. Rev. Nul. Part. Si 30 , 561 (1994). [2℄ C.W. Beausang et al. , J. Phys. G22 , 527 (1996). [3℄ S.L. Shepherd et al. , Nul. Instrum. Methods Phys. Res. A434 , 373 (1999). [4℄ S. Bouneau et al. , Nul. Instrum. Methods Phys. Res. A443 , 287 (2000). [5℄ P. Jones et al. , Ata Phys. Pol. B30 , 671 (1999). [6℄ J. Gerl et al. , GSI Sienti rep ort, 271 (1994). [7℄ M. Kaspar et al. , GSI Sienti rep ort, 195 (1997). [8℄ M. Leino et al. , Nul. Instrum. Methods Phys. Res. B99 , 653 (1995). [9℄ J. Heese et al. , Phys. Lett. B302 , 390 (1993). [10℄ G.D. Draoulis et al. , Phys. Lett. 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