2 nd Workshop on Inelastic Reaction Isotope Separator for Heavy Elements Nov. 19, 2010 KEK isotope separation system for β-decay spectroscopy of r-process nuclei Y.X. Watanabe, RNB group (KEK) 1. Outline 2. Multinucleon transfer reaction of 136 Xe+ 198 Pt 3. Gas catcher system for collection and separation 4. Detection system for lifetime measurements 5. Summary 1
Lifetime measurements around N=126 nuclei 83 209 Bi 82 204 Pb 206 Pb 207 Pb 208 Pb 81 203 Tl 205 Tl 207 Tl atomic number 80 79 78 77 76 196 Hg 194 Pt 193 Ir 192 Os 195 Pt 198 Hg 199 Hg 200 Hg 201 Hg 202 Hg 204 Hg 206 Hg 197 Au 205 Au 196 Pt 198 Pt multi-nucleon transfer 136 Xe+ 198 Pt 204 Pt 203 Ir 202 Os 5 10 8 years T 1/2 30 days T 1/2 < 5 10 8 years 10 minutes T 1/2 < 30 days T 1/2 < 10 minutes unknown 75 201 Re 74 200 W 116 117 118 119 120 121 122 123 neutron number 124 125 Lifetime measurements of N=126 nuclei in our 5-year project since 2010 Multinucleon transfer (MNT) reaction to access N=126 nuclei C.H. Dasso et al., Phys. Rev. Lett. 73 (1994) 1907. V. Zagrebaev and W. Greiner, Phys. Rev. Lett. 101 (2008) 122701. L. Corradi et al., J. Phys. G: Nucl. Part. Phys. 36 (2009) 113101. From 204 Pt down to 200 W by 136 Xe+ 198 Pt MNT reaction 126 2
KEK isotope separation system Focusing chamber - Electric-Q Triplet - Electric Deflector - Slit, Monitors Mass separator - Magnetic-Q Doublet - Magnetic Dipole - Magnetic-Q Doublet Detection system - 3 detector stations : tape-transport system : Multi-layered plastic scintillators : Ge detectors - β-decay spectroscopy Extraction chamber - Electric lens - Monitors Coolant inlet & outlet Stopping gas-inlet Laser 136 Xe Gas catcher system - Target ( 198 Pt) - Gas cell - Laser resonance ionization - SextuPole Ion-Guide 3
MNT reactions of 136 Xe+ 198 Pt Excitation functions for the production of N = 126 isotones Expected yields for N = 126 isotones cross section after evaporation (mb) 202 Os Os 201 Re Re 200 W 199 Ta Ta 198 Hf Hf 197 Lu Lu Yield (pps) 202 Os 200 W 136 Xe : 9 MeV/A, 2 pna 198 Pt : 12 mg/cm 2 E lab (MeV/A) σ ~ 10 1 mb for 202 Os σ ~ 10 3 mb for 200 W calculated by GRAZING code (http://personalpages.to.infn.it/~nanni/grazing) Mass A 5.0 pps for 202 Os 0.1 pps for 200 W 4
136 Xe + 198 Pt Contaminations σ (mb) Isobaric distribution (A=202) atomic number 198 Pt 202 Os N=126 isobar σ (mb) ~99.7% contaminations 202 Os ~0.3% neutron number atomic number Z and A separations are essential for the lifetime measurements of rare channel products. 5
Kinematic condition for 202 Os 198 Pt 202 Os 136 Xe 9 MeV/A 12 mg/cm 2 Angular distribution ~65 Energy distribution Yield (a.u.) Large and wide emission angle ~10 Yield (a.u.) Low energy, wide energy spread < 0.5 MeV/A ~ Angle ( degree ) Energy ( MeV/A ) Efficient collection and separation Gas catcher system 6
Gas catcher system - Laser resonance ionization + ISOL - Schematic view of gas catcher system Ar gas Gas cell filled with 500 mbar Ar gas 198 Pt 136 Xe 9 MeV/A gas flow Laser for ionization (Z selection) + + Ion source chamber (<0.1 mbar) + + ISOL A separation Extraction chamber (10 2 mbar) diameter : ~φ1 mm emittance : ~10π mm. mrad SPIG (SextuPole Ion Guide) V RF ~ V SPIG V end V ext V 0 ~ 60 kv Z and A separations are achieved by laser resonance ionization and ISOL. 7
Ar gas φ10 cm Gas cell design Cross-sectional view of stopping distribution ( 202 Os fragments) Top view of gas cell laminar flow 198 Pt target 0 1 2 3 4 5 cm 136 Xe 3 cm ion collector electrode laser Simulation by hydrodynamic calculations exit hole (φ1 mm) Stopping efficiency : ε stop = 87 % extracted yields (a.u.) survival probability 160 120 80 40 Transport time profile 0 0 200 400 600 800 1000 1200 1400 1.0 0.8 0.6 0.4 transport time ( msec ) Mean-time = 253 ms Transport efficiency : ε tra = 56% Survival probability of radioactive nuclei 0.2 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 half-life (sec) Survival probability : ε sur = 72% 8 (T 1/2 = 500 msec)
Laser resonance ionization Schematic diagram of atomic level autoionizing state λ 2 2 nd laser pulse intermediate state 1 st laser pulse λ 1 ionization E x g.s. λ 1 and λ 2 are intrinsic to each element Z selection E I Laser wavelength for ionization of stable isotopes (Z=69~78) λ 1 : 250 590 nm λ 2 : 220 460 nm λ 1 and λ 2 are known, but we need to confirm and search the most efficient ionization schemes excimer laser LPX204i dye laser ScanMate2E λ 1 dye laser FL3001 λ 2 Gas cell Frequency tunable dye lasers 9
Total efficiency of gas catcher system Total efficiency = ε stop ε trans ε surv ε LIS ε SPIG stopping transport survival = 0.17 = 0.9 Total efficiency 5.0% for 200 W (T 1/2 =423 ms predicted by KUTY) 6.8% for 202 Os (T 1/2 =2.38 s predicted by KUTY) half-life (sec) KUTY : T.Tachibana, M. Yamad, Proc. Inc. Conf. on exotic nuclei and atomic masses, Arles, 1995, p763. 10
Detection system Tape transport system Plastic scintillators for β rays two layer 1 mm t and 2 mm t back: 10 cm wide 20 cm height front: 4 cm radius 20 cm height ε β = 80% (for Q β = 4.5 MeV) Detection efficiency β-ray energy spectrum ε (%) S β (a.u.) 200 W from ISOL E β (MeV) E β (MeV) Ge detectors for X rays 10cm x 10 cm x 5 mm thick ε X = 60% (for 70 kev X-ray) Ge detectors for γ rays (option) 10cmx10cmx10cm long ε γ = 20% (for 500 kev γ-ray) 11
Switching box Beam Three detection stations 1st 2nd 3rd Beam-on/off time-sequence 1st station on switch 2nd station for 200 W (T 1/2 ~ 0.5 s) off on switch 3rd station T on = 1.0 s T off = 1.5 s T on T off 0.5 s off on on switch off survival probability (%) tape movement (50cm) off T on = T 1/2 2, T off = T 1/2 3 on 100 50 off on ~40% off T 1/2 = 0.5 s 0 12 0 1 2 -on time (s)
Collection efficiency Survival probability during -on Statistical estimation 200 W : production rate = 0.11 pps ~1 10 4 particles/day Good Z separation by laser resonance ionization (isobaric contaminations ~ 0.1%) Detection efficiency of β ray 5.0% ~40% 80% β-decay detection : ~160 counts/day Additional X-ray detection Emission probability of Kα 2 X ray Detection efficiency of X ray 16 % 60 % lifetime with 10% error Detection : ~16 counts/day lifetime with 30% error Au Pt Ir Os Re W Ta Hf Lu Yb 120 121 122 123 124 125 126 Region down to the red line could be accessed N T 1/2 (KUTY) 1 day 1 h 1 min 1 s 13 100 ms 10 ms
Summary Lifetime measurements for unstable nuclei produced by MNT reactions of 136 Xe+ 198 Pt in 5 years: 204 Pt~ 200 W (N=126) Gas cell + laser resonance ionization + ISOL rapid & efficient collection with laminar flow Z & A separation with laser resonance ionization & ISOL efficiency = 5.0% for 200 W (T 1/2 ~423 ms) Tape transport + β-decay measurements Three detection stations suppression of decay loss 160 counts/day for 200 W lifetime is determined with 10% error Research & Development in 2 years Multi-nucleon transfer reaction: feasibility Gas cell design: transport efficiency, transport time profile Laser resonance ionization: wavelength tuning for most efficient ionization-scheme Studies toward waiting nuclei Low-energy intense neutron-rich RIBs such as 140 Xe 14
Collaboration KEK H. Miyatake, S.C. Jeong, H. Ishiyama, N. Imai, Y. Hirayama, K. Niki, M. Okada, M. Oyaizu, Y.X. Watanabe RIKEN M. Wada, T. Sonoda, A. Takamine, Y. Ito, Y. Matsuo TITech T. Furukawa K.U. Leuven P. Van Duppen, Y. Kudryavsev, M. Huyse 15