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

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

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

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

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). . . ]

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

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.)

Multi-layered active target

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)

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

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 = 5.27 MeV deuteron: Ed = 2.66 MeV alpha: Ea = 1.34 MeV

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

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

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. . . .

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

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 (?)

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

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

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

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.

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