1. GRAPE(Gamma-Ray detector Array with Position and Energy sensitivity) Developed at CNS for in-beam  -ray spectroscopy with High Resolution M. Kurokawa@Heavy Ion Lab. I.Configuration of GRAPE consisting of segmented Ge detectors II.How to obtain sub-segment position sensitivity, which is necessary for the correction of Doppler shift 1.3-Dimensional understanding of the relation between the position of interaction and the generated pulse shape 2.Monte Carlo simulation to study the effects on the correction by applying the position information 3.The method to determine the position III.First results with a beam IV.Summary and future

2. Configuration of GRAPE Consisting of segmented planar detectors (side surface faces to a target ) Effective diameter is 6 cm and the thickness is 2 cm Front contact is divided into 9 segments Two crystals are encapsulated in one cryostat Detectors are arranged in three rings around the beam pipe. Each ring consists of up to 6 detectors. ----> total number of signal channels = 360 ch. photopeak efficiency and peak-to-total ratio can be 5% and 25%, respectively, for  -rays of 1 MeV energy resolution is 1.4% at  = 0.3 Z direction

3. How to obtain sub-segment position sensitivity? i. 3-Dimensional understanding of the relation between the position of an interaction and the generated pulse shape i. 3-Dimensional understanding of the relation between the position of an rise time of the signal from the segment where the interaction occurs maximum pulse height of the transient signal from neighbor segment exp. simulation hit Pulse shape, which can be predicted precisely by simulation, exhibits 3-dimensional position sensitivity smaller than segment size. M. Kurokawa et. al, IEEE Trans. on Nucl. Sci., 50 (2003) 1309.

4. ii. Effects on energy resolution of the position sensitivity Monte Carlo simulation code: GEANT4 beam target Projectile  = 0.3 E  = 3.7 MeV z (b) (c) central position  x, y:central position  z = 1 mm (FWHM)  Information along z-direction is most important

5. iii. The method to determine the position along z direction Schematical illustration of position dependence Pulse shape after CR 2 -RC 4 shaping (simulated in a step of 1 mm) Pick up these timings time V Z: shallow Z: deep Z: shallowZ: deep electron hole Longer drift time determines the rise time Same rise time But, due to the small pixel effect, These two pulses show the most drastical change at different time.

6. First results with a beam 4 He( 12 Be, 12 Be  ) reaction simulation experiment Ref.) S. Shimoura, Nucl. Instr. And Method, A525 (2004) 188.

7. Energy spectrum after the correction of Doppler shift Averaged position sensitivity is better than 3.4 mm First results obtained by utilizing the sub-segment position sensitivity at that time (2002) ? (cf. MINIBALL) 3.1% 1.4%

9. Summary and future Sub-segment position sensitivity is achieved by picking up the zero-cross timing after CR 2 -RC 4 shaping (better than 3.4 mm) The correction of Doppler shift improves the energy spectrum (1.4% at  = 0.3) without loosing the detection efficiency by utilizing the sensitivity Cf.) MINIBALL + EUROBALL (H. Wollersheim et. al, Nucl. Inst. and Method A537 (2005) 637.) Efficiency : 3% Resolution : 1.2 - 1.5 % at  = 0.43 Position sensitivity : 5 mm --> 1 % resolution Future: x and y position sensitivity to trace scattering points for high M  cf.) AGATA, GRETA ---> next speaker