Transcript GRAPE(Gamma-Ray detector Array with Position and Energy

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.
I.
Configuration of GRAPE consisting of segmented Ge
detectors
How to obtain sub-segment position sensitivity, which is
necessary for the correction of Doppler shift
II.
1.
2.
3.
III.
IV.
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
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
Z direction
 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 g-rays
of 1 MeV
 energy resolution is 1.4% at b = 0.3
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
<z direction> rise time of the signal
from the segment where the interaction
occurs
<x-y direction> 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.
ii. Effects on energy resolution of the position sensitivity
z
Monte Carlo simulation code: GEANT4
Eg = 3.7 MeV
Projectile
b = 0.3
beam
target
Dq
Dq
(b)
(c)
central position
x, y:central position
Dz = 1 mm (FW HM)
Information along z-direction is most important
iii. The method to determine the position along z direction
Schematical illustration of position
dependence
Pulse shape after CR2-RC4 shaping
(simulated in a step of 1 mm)
Longer drift time determines
the rise time
hole
electron
Z: shallow
Z: deep
Same rise time
V
Z: shallow
Pick up these timings
Z: deep
time
But, due to the small pixel effect,
These two pulses show the most drastical change at different time.
First results with a beam
4He(12Be, 12Be
simulation
g) reaction
experiment
Ref.) S. Shimoura, Nucl. Instr. And Method, A525 (2004) 188.
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)
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 --> 1 % resolution
•Future: x and y position sensitivity to trace scattering points for high Mg
cf.) AGATA, GRETA
---> next speaker