1. CNS Active Targets for Missing Mass Spectroscopy with RI beams Tomohiro Uesaka CNS, University of Tokyo
・　Missing Mass Spectroscopy
・ Two different missing mass spectroscopy with RI beams
Normal Kinematics
Multi-layered active target (to be made)
Inverse Kinematics
CNS active gas target　→　Akimoto's talk

2. Missing Mass Spectroscopy
Spectroscopic information is (primarily) extracted from properties of probe particle(s).
Normal kinematics: projectile/scattered particles
Inverse kinematics: target/recoiled particles
has been a basis of major activities at stable-beam facilities.
Inelastic scattering (p,p'), (d,d'), (a,a') . . .
Charge exchange (p,n), (d,2He), (3He,t)
Transfer (d,p), (p,d), (3He,d). . .
KEYWORDS: Selectivity & Sensitivity

3. Spin-isospin Selectivities
Strength of
Effective interaction
(DT, DS)=(0,0)
Gamow-Teller
DL = 0 , DT = 1, DS = 1
Fermi
Isoscalar monopole
DL = 0 , DT = 1, DS = 0
(1,1)
(1,0)
(0,1)
DS = 0
DS = 1
(p,p'), (d,d'), (a,a')
(p,p'), (d,d')
DT = 0
(p,p'), (p,n), (3He,t),
(p,p'), (p,n), (3He,t), (d,2He)
(6Li,6Be), (12C,12N)
DT = 1

4. Sensitivity: momentum transfer
If the reaction occurs in the vicinity of nuclear surface,
M. Itoh

5. Missing Mass Spectroscopy with RI beams
1. Normal kinematics experiments
New features available (only) by RI beam induced reactions
Search for new excitation modes :
major goal of SHARAQ experiments.
2. Inverse kinematics experiments
Investigation of structure of unstable nuclei
via traditional reactions
(a,a'), (d,2He), (3He,t) [, (d,p), (p,d), (3He,a). . . ]

6. Normal kinematics exp. @ SHARAQ
Spectroscopy with RI-beam induced reactions
Traditional example: (t,3He) experiments
extraction of b+ strength
POTENTIAL of (new) RI beam induced reactions
New SELECTIVITIES (DT, DS, DL, Dp)
missing in stable-beam induced reactions
ex. the (10C,10B*(IAS)) reaction to probe isovector non-spin-flip
(DT=1, DS=0) excitations.
→ search for Isovector Monopole Resonances
Access to kinematical region which are inaccessible by stable beams.
large Q-value in RI beam induced charge exchange reaction　(exothermic)
→　RECOILLESS excitation of HIGH-Ex states
Isovector Spin Monopole Resonance via the (12N,12C) reaction
Double Gamow-Teller Resonance via the (9C,9Be)/(20Mg,20Ne) reactions
Tetra-neutron state via the 4He(8He,8Be[=2a]) reaction

7. Target for high-resolution measurements
In many cases, target thickness is most critical.
ex. charge exchange reaction:
energy loss difference between projectile and ejectile.
For a better use of SHARAQ,
we need a “next generation TARGET system” such as
an active target, or a multi-layered target
with a sensitivity to reaction point.
target
Projectile
Projectile
DE(proj.)
DE(ejec.)

8. Multi-layered active target

9. Requirements Rate > 1MHz Charge resolution DZ=1 10C/10B 30%
Foil thickness ~ 30 mg/cm2 (DE = 1MeV )
Counter gas should be thinner than foil targets
A test bench will be made in FY2010.
(based on a beam-line detector)

10. Inverse kinematics experiments
incompressibility
ex. Extraction of Gamow-Teller strength
Population of Isoscalar monopole resonances
q = 60 MeV/c
Forward angle measurement is crucial

11. Recoil energy q = 100 MeV/c proton: Ep = 5.27 MeV
(Heavy) RI beam
light-ion target
p, d, a
q = 100 MeV/c
proton: Ep = MeV
deuteron: Ed = 2.66 MeV
alpha: Ea = 1.34 MeV

12. Kinematics 4He(68Ni,68Ni*)4He @ 200 MeV/u Ex = 0 MeV 10 MeV 20 MeV

13. a Range in 4He gas 0.1 MeV 6.9 mm (0.13 mg/cm2) 0.5 MeV 17.8 mm
As a result, an ``active'' target is necessary
for the (very) forward angle measurement

14. Yield Estimation Target thickness 3×1020 /cm2 (1 atm ×10 cm)
Integrated luminosity 0.1 mb (assumed)
→　105-pps (intense!) beam is needed for 300 events/day
How can we detect low-energy a particles
in the presence of 105-pps heavy ion beams?
considerable space charge effects

15. Our (tentative) solution: CNS (``In-'') Active Target
R. Akimoto,
S. Ota et al.
Top-view a
Beam-view
field shaping wires a
GEMs

16. Future experiments inelastic scattering to pin down monopole strengths
Optimization of gas pressure, purity (quencher concentration)
range ⇔ yield
(d,2He) reaction to extract b+ strength in the pf-shell region
Discrimination of two proton trajectories
use of flash ADC
Combined operation of the active target with
Magnetic spectrometer: SAMURAI, SHARAQ, Zero-degree
g-ray measurements: for better Doppler-correction (?)

17. Low-energy option (for CRIB/RIPS exp.)
Use of a polarized 3He gas as a counter gas
(3He,d) : proton particle state spectroscopy
(3He,2He): neutron particle state spectroscopy
(3He,a) : neutron hole state spectroscopy }
strong spin
selectivity a
3He

18. A little about Diamond detectors
・ SHARAQ exp. uses high-intensity (>1 MHz) beams.
・ Mass measurement by the high-resolution beam-line (& SHARAQ) requires good TOF resolution (≪50 ps)
→ Possible solution: diamond detector
Good time responses
Radiation hardness
A. Stolz

19. A little about Diamond detectors (cont.)
CNS-NSCL collaboration is being started:
3×3 cm2 detector
A. Stolz
Issues: large bandwidth preamplifiers
electronics for 10-ps timing measurement

20. Summary Multi-layered active target
for normal kinematics experiments at SHARAQ
Only "idea", a test bench will be made soon.
CNS active gas target
for inverse kinematics measurement
has been tested for a low-energy alpha beam
→ Akimoto's talk
Diamond detectors
CNS-NSCL collaboration → 3×3 cm2
electronics to achieve time resolution of 10 ps should be
developed.

21. Collaborators Multi-layered active target Diamond detector
SHARAQ collaboration (U-Tokyo, RIKEN,NSCL, etc)
CNS active gas target
R. Akimoto, S. Ota, T. Gunji, S. Michimasa, H. Tokieda
S. Kawase, T. Tsuji, H. Hamagaki, T. Uesaka
T. Hashimoto, H. Yamaguchi, S. Kubono (→ MSTPC)
+ T. Kawabata, T. Isobe, Tsukuba group