Polarized 11 Li beam at TRIUMF and its application for spectroscopic study of the daughter nucleus 11 Be 1. Physics motivation new  delayed decay spectroscopy using polarized nucleus 2. Polarizer for RNB at TRIUMF ISAC polarization by collinear optical pumping special cares to achieve high polarization 8 Li: 80%, 9 Li: 56%, 11 LI: 55%, 20 Na: 57%, 21 Na: 56%, 26 Na: 55%, 27 Na: 51%, 28 Na: 45% 3. Experimental results with polarized 11 Li beam spin-parity assignments of levels in 11 Be 4. Summary T. Shimoda 1, Y. Hirayama 1,2, H. Izumi 1, H. Hatakeyama 3, K.P. Jackson 4, C.D.P. Levy 4, H. Miyatake 2, M. Yagi 1, H. Yano 1 1: Osaka Univ., 2: KEK. 3: Univ. of Tokyo, 4:TRIUMF CONTENTS

β-delayed decay spectroscopy polarized assignment a new method of β-delayed decay spectroscopy β-decay from a spin polarized nucleus  -decay angular distribution A takes very different values depending on the final state spin. A: asymmetry parameter of allowed  -decay P: polarization of the parent nucleus ～0～0 11 Li → 11 Be

Measurement of β-decay asymmetry R-detector L-detector polarization : β-ray counts when spin orientation is reversed free from instrumental asymmetry

Excited States of 11 Be F. Ajzenberg-Selove, Nucl. Phys. A506 (1990) 1. ■ only a few spin-parity assignments prevents comparison between experiment and theory level by level ■ low level density at high energy region 11 Be 10 Be n S 1n =504 keV T 1/2 = 8.5 ms Most of the states decay by neutron emission.

Isotope Separator / ACcelerator radioactive nuclear beams produced in target fragmentation induced by a 500 MeV 100  A proton beam TRIUMF ISAC commissioned in Aug. 2001

Alkali RI beam from ISOL A +1 beam at 10 – 60 keV neutralizer charge exchange in a Na vapor jet A +1 + Na → A 0 + Na +1 : 90% efficiency optical pumping for fast neutral beam in collinear geometry two laser beams to pump the two ground-state hyperfine levels longitudinal polarization re-ionizer collision with a cold He gas target (12K) A 0 → A +1 : 66% efficiency transversely nuclear-polarized ion beam bend

1.9 m Shimoda 11 Li decay spectroscopy Minamisono A Na moments,  -decay symmetry Kiefl 8 Li  -NMR condensed matter physics neutralizer re-ionizer unpolarized 11 Li keV polarized 11 Li +1 B→ 10Gauss beam velocity tuning C.D.P. Levy et al. Nucl. Instr. and Meth. B204 (2003) 689 TRIUMF ISAC Polarized Beam Line pumping within 2.6  s

D1 673 nm 905 MHz laser freq. pumping the two ground-state hyperfine levels in order to achieve high polarization

Electro-Optic Modulator (EOM) Only 1/3 laser power is used for each optical pumping. driven at the hyperfine splitting frequency

>> laser line width ～ 1 MHz energy (Doppler) broadening of the neutralized beam multiple collisions with Na atoms in the neutralizer 6.3 eV

EOM-2 19 MHz EOM-3 28 MHz two EOMs in series broadening the laser line width laser beam 8 Li P ～ 20% P ～ 70%

AP (coin. with 0.32 MeV  ) = － 0.43 ± known A = -1 Polarization measurement = 0.80 (  0  opening angle of the  -detector) = 0.98 (  = 12.3 ms, T 1 = 570 ms in Pt  -1.0 (3/2 - → 1/2 - ) 11 Li: P = 0.55 ± Li simulation by rate equation

E903 at TRIUMF Li-glass scintillator: Δ  n = 0.92% x 2,  n keV,  n = keV En ≧ 1 keV Flight Length: 130 mm Ge detector: HPGe, 50 and 60 %,  Δ     = MeV plastic scintillator: Δ  n = 1.8% x 6,  n = MeV, En ≧ 500 keV Flight Length: 1.5 m  -ray telescope: Δ   = 14.7% x 2,   = 90% -3  - n,  - n-  - , coincidence keV E n = 1 keV – 9 MeV Detector Setup 11 Li gs 11 Be*+  10 Be* + n 10 Be gs + 

Y. Hirayama et al., Phys. Lett. B611 (2005) 239 neutron TOF spectrum and coincident  -decay asymmetry high energy neutrons 11 Li gs 11 Be*+  10 Be* + n

New Level and Decay Schemes of 11 Be E x, I  log ft spectroscopic factor 11 Li→ 11 Be → 10 Be + n determined ■ ■ ■ decay path ■

F. Ajzenberg-Selove, Nucl. Phys. A506 (1990) 1. Y. Hirayama et al., Phys. Lett. B611 (2005) 239

Summary ● Highly polarized (50 – 80%) radioactive nuclear beams of alkali ions (Li, Na) have been successfully produced at the collinear optical pumping system of TRIUMF ISAC. The success was due to (i) pumping of the two ground-state hyperfine levels and (ii) matching of the laser line width to the Doppler broadened absorption line of the beam. ● The highly polarized beam is a very powerful tool to explore the excited states of unstable nuclei by applying the new method of  -delayed decay spectroscopy. The  -decay asymmetry parameter is useful (i) to assign the peaks of the decaying particles and (ii) to assign the spin-parity of the daughter states.

Ring dye laser Coherent Dye: DCM SPECIAL/LC W 673 nm cw circular polarized for 11 Li frequency reference to actively stabilize the ring dye laser  8mm  12mm Laser system

8 Li: 80%, 9 Li: 56%, 11 LI: 55%, 20 Na: 57%, 21 Na: 56%, 26 Na: 55%, 27 Na: 51%, 28 Na: 45% Achieved polarization Pumping for 11 Be + beam is in progress.

Doppler-shift tuning deceleration bias (Na vapor cell) tuning to adjust ion beam velocity so as to meet the Doppler shift absorption line scanning velocity 11 Li

D1 transition frequency/wave number for Li atoms at rest cm GHz cm -1 Doppler shift cm keV 11 Li Na vapor cell bias tuning 1 eV → 17.8 MHz

R.E. Azuma et al., Phys. Rev. Lett. 43(1979) He ionization chamber thermal neutron Low energy neutrons spurious due to resonance in detector 16 keV 72 keV high energy neutrons 6 Li-doped scintillators

 -decay asymmetry E n = 72±5 keV  = 25±15 keV      = 3/2 -  -detector = L+, L -, R+, R - laser helicity E n = 16±1 keV  = 9±3 keV      = 5/2 -

Low energy neutrons 12±2.6 % 5.1±1.5 %

AP (peak B) = － ±  (solid angle) =0.80  (spin relaxation) =0.98 P = ±  coincidence Doppler broadening due to neutron recoil 100±50 fs β-decay n-decay γ-decay γ-rays

mixed but one is dominant  n coincidence hidden peaks ! spin-parity assignment High Energy Neutrons

β-n-γ-coincidence existence previously claimed by Aoi et al.

neutron energy neutron detection efficiency curve level width → neutron peak profiles ✓ check the calculated neutron peak profiles Γ=216±55 keV Γ=243±55 keV β-n-γcoincidence 5 7 ✓ reproduction of spectra based on observed decays and assigned spins-parities reproduction of spectra based on observed decays and assigned spins-parities ✓ detector time resolution ✓ spin-parity ✓ → asymmetry spectrum

further included neutron decays from known levels from assumed levels reproduction of spectra by including unknown neutron decays from known levels and assumed levels reproduction of spectra by including unknown neutron decays from known levels and assumed levels

New Level and Decay Schemes of 11 Be E x, I  log ft spectroscopic factor 11 Li→ 11 Be → 10 Be + n determined ■ ■ ■ from known levels from assumed levels previously unknown transitions

neutron spectroscopic factor 11 Be → 10 Be + n neutron penetrability : partial decay width channel radius l –th order Hankel function of the first kind overlapping between 11 Be and 10 Be

K  = 1/2 － K  = 3/2 － Anti-symmetrized Molecular Dynamics Anti-symmetrized Molecular Dynamics K  =1/2+ Y. Kanada-En’yo and H. Horiuchi, Phys. ReV. C66 (2002) Y. Kanada-En’yo, H. Horiuchi, A. Dote, Nucl. Phys. A687 (2001) 146c ab-initio fully microscopic theory without any model assumptions such as mean field, clustering, ・・・ K  = 1/2 － K  = 3/2 － K  =1/2+ ■ 2α-cluster states (α+α+3n) rotational bands ■ single-cluster state (α+5n+2p) single cluster state 3n: p-shell (0hω) 2n: sd-shell (2hω) 1n: sd-shell (1hω) log-ft

Spectroscopic Factor assumed lowest possible L Transitions with the largest spectroscopic factor are shown. ? ? new cluster states?