1. Naohito Iwasa Dept. Phys., Tohoku Univ.
Silicon strip detectors and plastic scintillator hodoscope for Coulomb dissociation experiments
Naohito Iwasa
Dept. Phys., Tohoku Univ.

2. Motivation Coulomb dissociation method
powerful tool to study nuclear astrophysics and nuclear structure.
7Be+p 8B
The 7Be(p,g)8B reaction: solar neutrino
8B＋high-Z target→7Be+p
8B + 208Pb → 7Be + 1H + 208Pb
　　 　　　　↓ (~1000/MeV)
8B + g → 7Be + 1H
↓ ~1000
7Be + 1H → 8B + g
High precision (Large cross section)
Thicker target can be used (high energy)
High detection efficiency (charged particle detection)
Momenta and scattering angles of 7Be and p

3. 1989～2000 (RIKEN) 13N(p,g)14O: SSD+CsI(Tl) EMRIC
7Be(p,g)8B, 8B(p,g)9C, 11C(p,g)12N, 12N(p,g)13O: plastic scintillator hodoscope
Hodoscope 1
1m×1m active area
　ΔE:5mmt, E1: 60mmt
　ΔE: 　 X:100mm× 1m
　E1: Y: 60mm × 1m
　10 × 16 segments
He gas
Hodoscope II
ΔE:5mmt, E1: 60mmt , E2: 60mmt
　ΔE: 　 X:100mm(or 40mm)× 1m
　E1,E2: Y: 75mm(or 38mm) × 1m
　13 × 16 segments
　position resolution θ<1.1 degrees
vacuum
Hisanaga, diploma thesis
Scattering angles:
position of hit on hodoscope
time difference
momenta: TOF　　(s～0.6ns)
PI: ΔE-E

4. 8B results（example） S17=18.9±1.8 eV b
1. Motobayashi et al., Phys Rev. Lett. 73, 2680(1994)
Iwasa et al., J. Phys. Soc. Japan, 65,1256(1996)
2. Kikuchi et al., Phys. Lett. B391, 261 (1997)
Eur. Phys. J., A3, 213 (1998)
S17=18.9±1.8 eV b

5. Heavier system (2000～)
Particle identification of heavy ions(HI) using plastic scintillators is difficult!!
→ Silocon strip detectors are installed between the target and hodoscope.
　　to measure scattering angle of proton and HI, PI and kinematical energy of HI
Energy loss of HI is higher than that of proton (～600 for 35K+p case)
Detection efficiencies of proton and HI are high.
4-5 layers
1st and 2nd layers: silicon strip detector
3rd&4th(&5th&6th) layers: silicon detector
～68cm

6. Silicon strip detectors
1st: x
2nd : y
p side
n side
3,4,5,6 layers
23Al,27P: 8 detectors
20Mg, 31Cl, 36Ca :
21detectors
21 silicon detectors (50×50 mm2 active area, 0.3 mmt , 5mm pitch, mounted on 56×56 mm2 frames) Δθ～ 1.5 degree(σ)
21 silicon detectors → 5-7 groups.
p side: high gain: proton O, HI: overflow
n side: low gain: proton ×, HI: O
p: Cf=33pF or 47pF, n: Cf=270pF

7. readout p side High gain PA SA ADC V785 Cf=33(47)pF Bipolar
P: MeV ～1mV
HI:
Noise- proton separation
no saturation
Z≦17(27P) OK
Z= 20(36Cl) we will try.
RC～0.1ms　→　resolution?
Low gain
n side PA SA
ADC
V785
Bipolar
Cf=270pF
TFA
CFD
delay
TDC
V775

8. Results of silicon detectorsH He HI
overflow
SSD strip side
noise
Cf=33pF
T. Gomi, Thesis
E resolution
0.6%
PI and energy
of HI
DE[ch]
angle
hodoscope He d
DE[ch]
PI of proton
Velocity of proton
E[ch] p H
Invariant mass
TOF+offset[ns]
TOF+offset[ns]

9. Results
T.Gomi et al., J. Phys. G31, S1517 (2005).
Y. Togano et al., Nucl. Phys. A758, 182c (2005).
1.372
3.4
1.77
2.7
0.55
2.0(new!)
0.125
1.6
22Mg+p
23Al
1.2
0.90
26Si+p
27P

10. Experiment at higher energies
GSI: Coulomb dissociation of 8B at 254AMeV
Coulomb dissociation of 6Li
advantages
High beam intensity, thicker target, M1 component↑, E2 component ↓
On the other hand,
DE-E method → Br-DE-TOF method
reaction loss several% → several 10%
forward focus → precise measurements of scattering angle and momenta
is necessary

11. GSI (8B) 254AMeV 8B 1.6T Silicon strip detector
58×58 mm2, 0.3mmt, 0.1mm pitch
GASSIPLEX+CRAM

12. GSI (silicon strip detector)
58×58 mm2, 0.3mmt
0.1mm pitch single side
576 ch×4 = 2304 ch
GASSIPLEX chip (16ch/chip, 64ch/board)
(preamp+shaping amp+multiplexer)
Analogue multiplex technique + CRAM

13. GSI experiment x y Z Vertex Target p 7Be q17 X Y X Y 4.6mrad 14cm 31cm
SSD1/SSD2
SSD3/SSD4 Z
Vertex
Target p
7Be
q17
z-vertex
position X Y X Y
4.6mrad
14cm
31cm
background fee

14. Results
Iwasa et al., Phys. Rev. Lett. 83, 2910 (1999) S17=20.6±1.2±1.0 eV b
Schümann et al, Phys. Rev. Lett. 90, (2003).
Phys. Rev. C73, (2006) S17=20.6±0.8±1.2 eV b
Adopted: eV b
4.8mrad, 0.3%

15. Conclusion Silicon strip detectors + plastic scintillator hodoscope
→ useful to study unbound states relevant to nuclear astrophysics and nuclear structure for A<40
For A≧40, other methods should be considered.
higher energies
ΔE(HI)/ΔE(p)～2000 for 101Sb→ Sn+p or RP process A<110
Pre-AMP and AMP with high dynamic range are needed.
VA chips with high dynamic range: AMS-02, VA32HDR11
For lower noise level, development of PreAMP, AMP chips is desired.