GRAPE(Gamma-Ray detector Array with Position and Energy sensitivity) Developed at CNS for in-beam g-ray spectroscopy with High Resolution M. Kurokawa@Heavy Ion Lab.

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GRAPE(Gamma-Ray detector Array with Position and
Energy sensitivity) Developed at CNS for in-beam
g-ray spectroscopy with High Resolution
M. Kurokawa_at_Heavy Ion
Lab.

• Configuration of GRAPE consisting of segmented Ge
  detectors
• How to obtain sub-segment position sensitivity,
  which is necessary for the correction of Doppler
  shift
• 3-Dimensional understanding of the relation
  between the position of interaction and the
  generated pulse shape
• Monte Carlo simulation to study the effects on
  the correction by applying the position
  information
• The method to determine the position
• First results with a beam
• Summary and future

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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. ----gt total number of signal channels
  360 ch.
• photopeak efficiency and peak-to-total ratio can
  be 5 and 25 , respectively, for g-rays of 1 MeV
• energy resolution is 1.4 at b 0.3

Z direction
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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
ltz directiongt rise time of the signal from the
segment where the interaction occurs
ltx-y directiongt maximum pulse height of the
transient signal from neighbor segment
exp.
simulation
hit
M. Kurokawa et. al, IEEE Trans. on Nucl. Sci., 50
(2003) 1309.
Pulse shape, which can be predicted precisely by
simulation, exhibits 3-dimensional position
sensitivity smaller than segment size.

• 3-Dimensional understanding of the relation
  between
• the position of an

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ii. Effects on energy resolution of the position
sensitivity
z
Monte Carlo simulation code GEANT4
Projectile b 0.3
Eg 3.7 MeV
beam
target
Dq
Dq
(c)
(b)
central position
x, ycentral position Dz 1 mm (FWHM)
Information along z-direction is most important
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iii. The method to determine the position along z
direction
Pulse shape after CR2-RC4 shaping (simulated in a
step of 1 mm)
Schematical illustration of position dependence
Longer drift time determines the rise time
hole
electron
Z shallow
Z deep
Same rise time
Pick up these timings
Z shallow
V
Z deep
time
But, due to the small pixel effect, These two
pulses show the most drastical change at
different time.
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First results with a beam
4He(12Be, 12Be g) reaction
experiment
simulation
Ref.) S. Shimoura, Nucl. Instr. And Method, A525
(2004) 188.
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Energy spectrum after the correction of Doppler
shift
3.1
Averaged position sensitivity is better than 3.4
mm
1.4
First results obtained by utilizing the
sub-segment position sensitivity at that time
(2002) ? (cf. MINIBALL)
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Summary and future

• Sub-segment position sensitivity is achieved by
  picking up the zero-cross
• timing after CR2-RC4 shaping (better than 3.4
  mm)
• The correction of Doppler shift improves the
  energy spectrum (1.4 at b 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
b 0.43 Position sensitivity 5 mm --gt 1
resolution

• Future x and y position sensitivity to trace
  scattering points for high Mg
• cf.) AGATA, GRETA
• ---gt next speaker