1. (g, n) (g, p) experiment at SAMURAI
RIKEN Nishina Center
Ken-ichiro YONEDA
22 Dec, 2009
Detector Workshop for RIBF experiments

2. SAMURAI (Superconducting Analyser for MUlti-particles with Radio-Isotope beams)
Spectroscopy of
Unbound States e.g. (g,n)
(p,2p) Missing Mass
Nucl. Astrophys. (p,g)
Deuteron expts for 3NF
Nucl. Matter
Bending Magnet
Superconducting
Large B・L (7Tm)
Large pole gap (80cm)
Weight ~ 600 ton
Neutron
Tokyo Tech. Group
(Prof. Nakamura)
in charge
d setup
TPC
Heavy Ion
(not shown
in picture)
Proton
(not shown
in picture)

3. Invariant Mass Method 12Be 14Be 14Be* n n 12C target 2+ ErelEx
12Be+n+n
S2n=1.26(13)MeV 0+
Scattering angle q
T.Sugimoto et al.PLB654,160(2007). 3

4. Coulomb Breakup Inelastic Scattering 19C+p→18C+n+X 17C+p→17C+n+X
11Li+Pb→9Li+n+n+X
T.Nakamura et al., PRL 96, (2006)
Y.Satou,TN et al., PLB 660, 320 (2008).

5. Physics of Neutron-rich Nuclei
via Invariant Mass Method
Structures and reactions
of r-process nuclei
Giant and Pigmy resonances
of Neutron-skin nuclei
Neutron Star/Nuclear Matter 82
r-process
126 50 82 28 20 50
Drip-Line Physics
Giant Halos? 2n, 4n-correlation?
New Cluster/Molecular States?
States beyond drip-lines? (4n,28O, and more) 8 28 20 2 8 2

6. NEBULA Typical Setup Detectors: To be installed
in the vertical direction
To cover more acceptance
in the horizontal direction
1.8m
(12cm thick x 2 layers) X 4 Walls
3.6m

7. NEBULA Modules Neutron Detector Module Veto Detector Module 32cm 12cm
Plastic Scintillator (BC408)
12cm(H)x180cm(H)x12cm(D)
Coupled to 2 PMT’s (HAMAMATSU R7724ASSY)
Veto Detector Module
Plastic Scintillator (BC408)
32cm(H) x 190cm(H) x 1cm(D)
Coupled to 2 PMT’s (HAMAMATSU R7724ASSY)
180cm
190cm
VETO
Module
Neutron
Module

8. Typical Setups of NEBULA
1n + core fragment
1-stack configuration
4n + core fragment
4-stack configuration
3.6m
~1m gap
10 m
@250MeV/u

9. Acceptance 2n acceptance 1n acceptance
Acceptance is dictated by neutron
Basic setup Horizontal -10deg~+10deg, Vertiacl -5deg~+5deg
1n acceptance
1n acceptance
2n acceptance
Smooth dependence and sufficient acceptance up to Erel=10MeV(40%)
2n acceptance has nearly identical E-dependence to that of 1n acceptance

10. Intrinsic efficiency for neutron Estimation of Resolution
96cm
48cm
12cmx12cm dimension is o.k.
In terms of the energy resolution
Thickness: 96cm  ~66%
(Thickness of 2m does not
enhance the efficiency very much)
Current (Half is funded)~40%

11. Current Status and Schedule
Half the neutron detector modules(120) +Full Veto Modules (48) are funded
1n efficiency~40%, 2n efficiency ~10%
(170 M JPY ~1.6M USD, 1MJPY/1module)
For the funded part,
Plastic Scintillators+PMT’s are available by the end of March 2010
(Modules for 1Layer already installed)
Electronics modules are available by the middle of 2011

12. Reaction Study for Nuclear Astrophysics
Very hot dense enviroment
particle capture
b decay
occurs sequentially
Important to understand
Natural abundance
Ongoing nucleosynthesis
from cosmic g-rays
Energy production in stars
….. {
Ne nova
M.Wiescher et.al.
Phil. Trans. R. Soc. Lond. (1998)

13. Nuclear Astrophysics Studies with Radioactive Isotope
Radioactive Isotopes are included
Short-life nuclei – hard to study
Structure theories are used – not always valid
change of shell structure, shape,…
 Experimental information is desired
Recent development of RI beams
In-flight fragmentation (fission)
 providing great opportunities to study
short-life RI reactions

14. Coulomb Breakup Reaction -- Inverse of (p,g) reaction --
22Mg
23Al*
23Al γ p
Incident beam
22Mg + p
23Al
High-Z
target (Pb)
22Mg(p,g)23Al 23Al(g,p)22Mg 26Si(p,g)27P 27P(g,p)26Si s ~ 60nb s ~ 4mb
Inverse reaction
Cross section far larger
Detailed valance + virtual photons

15. Experimental setup - Detectors for Heavy Ion and proton -
22Mg
Energy
Angle
Heavy Ion
Proton of
Invariant mass, Relative energy spectrum

16. Relative Energy Spectrum - 23Al  22Mg + p -
1st excited state
(objective state)
Higher excited state
continuum component: E1 ,
constant astrophysical S -factor
Counts /150keV
1000
2000
3000
4000
Relative energy [keV]
・ energy resolution 170 keV (Erel = 400 keV)
・ identify reaction through the first excited state clearly.

17. Cross sections - 23Al  22Mg + p -
Coulomb + Nuclear
l = 2
23Al
22Mg P
23Al *
l = 1
“βC” = “βN”
Small “Nuclear” component : 8 %
l = 2
distorted-wave calculation
optical potential : 17O+208Pb (84AMeV)
collective (vibrational) model
Coulomb ONLY
Coulomb + Nuclear
Coulomb and nuclear response is considered
as same deformation parameter.
Nuclear ONLY
= (7.0 ±1.3) × 10-7 eV
Compatible with the predicted value
by J.A. Caggiano et.al. Phys. Rev. C 64 (2001)
5.49×10-7 eV

18. Competition with b decay
Nucleosynthesis
in explosive hydrogen burning
(Novae, X-ray bursts)
T [GK]
106
104
102
100
ρ [g/cm3]
Which?
Nova Model
M1 : J.Jose et al Astrophys. J (1999)
M2 : C. Iliadis et.al. Astrophys. J. Supp (2002)
Cosmic
γ-emitter
Ne nova
M.Wiescher et.al.
Phil. Trans. R. Soc. Lond. (1998)
βdecay is favored

19. さらに重い領域へ Requirements 重い領域へ展開したい ・ 重い不安定核の生成 ・ 実験の分解能の向上
　　rp-process の waiting point となりうる所での反応レート
　　p-nuclei の起源、天然存在比の理解
Requirements
・ 重い不安定核の生成
RIPS　 RIBF + BigRIPS
・ 実験の分解能の向上
Silicon Telescope
SAMURAI spectrometer
resolution ~ 1/700
up to 100Sn
Thielemann et al., Prog. Part. Nucl. Phys. 46 (2001) 5.

20. PI, momentum of Heavy ion
low resolution mode
high resolution mode
PI, momentum of Heavy ion
PI, momentum of proton(s)
Strip Silicon Detectors
emission angles of products
Strip Silicon Detectors
Simultaneous detection of HI and p (sometimes 2p)
Small multiple scattering effect
Position measurement for relative angle

21. Silicon Strip detectors for proton breakup at SAMURAI
HEAVY ION
A/Z ～ 2
Developments Required
Broad Dynamic Range Both proton & HI (Z<50) hit the detector
Low-noize (non-linear?) Preamplifier
Low-noize circuit board & wire bonding
Capability of high density signal processing signals of about 2500 ch in total
Modify integrated ASD circuit HINP16C in collaboration with Texas A&M and Washington Univ. in St. Louis
HINP16C – 16ch processing in 1 chip
two output for energy and timing
PROTON
Silicon Strip
(x, y, (diag)) x2
HPK “GLAST” silicon
87mm x 87mm, 228 mm strip
RI Beam
e.g. 64Ge
 NEXT Talk by Kurokawa san
for more technical details
T. Ohsugi et al., NIM A541 (2005) 29

22. Summary (gamma, n) experiment (gamma, p) experiment
Invariant mass spectroscopy of neutron-rich isotopes
NEBULA detector
40% efficiency (Full volume), 100% coverage up to Erel ~ 3MeV
Half volume ready in March 2010
(gamma, p) experiment
Mainly for nuclear astrophysics interests
Silicon strip detector Readout requires
1:5000 dynamic range
2500 ch high dense signal prosessing
 NEXT Kurokawa san’s talk