Observation of Bound-State β Decay of Fully Ionized 207 Tl at the FRS-ESR 9 th Feb / Ryo Koyama Master’s Program in Fundamental Science of Matter, Graduate School of Science and Technology, Niigata University --- OUTLINE --- Introduction What’s a bound-state β decay ( )? Goal of present study Experimental method Production of fully ionized 207 Tl beam Beam cooling Schottky mass spectrometry Experimental results Data analysis Results Summary Summary and future prospects β b

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 1 β decay for neutral/bare atom SIS-FRS-ESR EXPERIMENTS Neutral atomBare atom β decay: n → p + e + ν remaining in a bound atomic state Bound-state β - decay ( decay) β b Continuous-state β - decay ( decay) β c

Goal of present study SIS-FRS-ESR EXPERIMENTS 9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 2 II. Evaluate the beam purity of 207 Tl 81+ … establish the experimental technique using secondary beam, cf 163 Dy [1], 187 Re [2] III. Evaluate the beam-cooling time... first application of stochastic pre-cooling prior to electron cooling I. Observe the β b decay of 207 Tl 81+ … derive the decay rates, and compare them with theoretical calculations → Apply the experimental technique to the β b decay experiment of 205 Tl which has been postponed because of its toxicity, will be feasible [1] M. Jung et al., PRL 69 (1992) 2164, [2] F. Bosch et al., PRL 77 (1996) ν Tl 0+ → 205 Pb 1+ + e - : E th 〜 50keV Most sensitive to the pp-neutrino Transition probability is unknown [3] K. Yokoi et al., AA 145 (1985) 339, [4] M.S. Freedman et al., Science 193 (1976) → Measuring the β b decay rates gives directly the ν-capture cross section [4] 205 Tl 81+ → 205 Pb ν : β b decay Solar ν problem: SSM pred. >> obser. s-process chronometry 205 Pb/ 205 Tl pair would be a short-lived s-process chronometer → Precise determination of β b decay rates is required [3] ⇔ β b decay has been totally overlooked !

Accelerator facility at GSI Gesellschaft für Schwerionenforschung, Darmstadt, Germany 9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 3 Outline of experimental method SIS-FRS-ESR EXPERIMENTS I. Production of 208 Pb II. Pre-acceleration up to 〜 11 MeV/u III. Acceleration up to 〜 830 MeV/u IV. 208 Pb + 9 Be Projectile fragmentation V. Separation of 207 Tl 81+ using Bρ-ΔE-Bρ technique VI. Electron cooling with stochastic pre- cooling VII. Observation of β b decay by the Schottky mass spectrometry (SMS)

Slits Wedge degrader 〜 830 MeV/u 208 Pb beam from SIS 4015 mg/cm 2 9 Be target SIS-FRS-ESR EXPERIMENTS 9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 4 Separation in the FRagment Separator (FRS) ΔE ∝ (z/v) 2 → v ∝ z/ΔE 1/2 Particle identification by Bρ-ΔE - Bρ method to ESR Bρ∝m/q･vBρ∝m/q･v -- Result of “MOCADI [5]” simulation -- [5] N. Iwasa et al., NIM B 126 (1997) 284. Bρ∝m/q･vBρ∝m/q･v Cocktail beam

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 5 Beam cooling in the Experimental Storage Ring (ESR) SIS-FRS-ESR EXPERIMENTS Stochastic pre-cooling Electron cooling ESR Injection from SIS / FRS Ion beam → Reduce δP/P down to 〜 → Reduce δP/P down to 〜 10 -6

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 6 Schottky Mass Spectrometry (SMS) SIS-FRS-ESR EXPERIMENTS ρ(Tl) > ρ(Pb) → C(Tl) > C(Pb) → f rev (Tl) < f rev (Pb) f rev = v/C Bρ∝m/q･vBρ∝m/q･v B(Tl) = B(Pb) q(Tl) = q(Pb) = 81 v(Tl) = v(Pb) ← cooling m(Tl) > m(Pb) Bρ∝m/q･vBρ∝m/q･v ････ Observation time → Intensity(t) Fourier transform Int.(t) → Int.(f rev ) Intensity(f rev ) Frequency Intensity ∝ Nq 2

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 7 Time dependent decrease/growth of Tl/Pb peak SIS-FRS-ESR EXPERIMENTS consists of 50 freq. spectra

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 8 χ 2 fitting to the decay/growth curve of Tl/Pb SIS-FRS-ESR EXPERIMENTS N Tl (t) = N Tl (0)exp(-λ tot t) βbβb βcβc λ tot = λ +λ +λ A.I., N Tl (0), N Pb (0) λ βcβc, λ βbβb → = λ N Tl (t) - λ A.I. N Pb (t) βbβb dN Pb (t) dtdt N Pb (t) = N Tl (0){exp(-λ A.I. t) - exp(-λ tot t)} + N Pb (0)exp(-λ A.I. t) λ tot - λ A.I. βbβb λ

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 9 Comparison with theoretical calculation SIS-FRS-ESR EXPERIMENTS The ratio of / is in agreement within an experimental uncertainty λ βbβb λ βcβc ⇔ ⇒ λ βbβb λ βcβc Some theoretical assumptions are not good enough, to calculate individual value of or ? Successfully observed β b decay of fully ionized 207 Tl ! Individual value of or is systematically small than theoretical calculation [6] λ βbβb λ βcβc [6] K.Takahashi et al., NP A 404 (1983) 578. T 1/2 ( β b + β c ) = 256 s is 〜 10% shorter than that of neutral atom 286 s [7] [7] M.J. Martin et al., NDS 70 (1993) 315. TC: theoretical calculation WM:weighted mean ■:: standard deviation

Purity of injected 207 Tl 81+ beam SIS-FRS-ESR EXPERIMENTS 9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 10 Contamination ratio = N Pb (0) N Tl (0) + N Pb (0) x 100 [%] → Purity of nearly 99% was achieved !

[8] T. Ohtsubo et al.,GSI Rep (2001) 15. → Nearly 90% reduction of the beam-cooling time compared to those at the previous experiments [8], where only the electron cooling was applied 9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 11 Improved beam-cooling time SIS-FRS-ESR EXPERIMENTS Electron cooling only Stochastic pre-cooling + Electron cooling 〜 9 sec 〜 60 sec Time after injection FFT frequency [a. u.] Injection→

9 th Feb / R. Koyama - Observation of Bound-state β - Decay of Fully Ionized 207 Tl at the FRS-ESR P. 12 Summary and future prospects SIS-FRS-ESR EXPERIMENTS We successfully observed bound-state β - decay of fully ionized 207 Tl via the projectile fragmentation at the FRS-ESR. We applied stochastic pre-cooling prior to electron cooling for the first time. We could reduce the beam-cooling time by about 90% compared to those at the previous experiments. The experiment using 205 Tl which has been postponed, is now feasible. 205 Tl is expected to be available as an experimental probe for the study on the s-process chronometry and/or solar neutrino problem. We succeeded to reduce the number of 207 Pb 81+ ions down to roughly 1%. Derived individual value of λ or λ is systematically small than the theoretical ones. This fact suggests that some theoretical assumptions are not good enough. βbβb βcβc Derived bound-to-continuum branching ratio λ /λ is in agreement with theoretical one, within an experimental uncertainty. βbβb βcβc

Thank you for your kind attention !! I am grateful to all the people who have helped to make this work successful. Especially, following people are highly acknowledged: Prof. F. Bosch 1, Prof. H. Geissel 1, Prof. G. Münzenberg 1, Assis. T. Ohtsubo 2, Prof. S. Ohya 2, Dr. C. Scheidenberger 1, Prof. T. Suzuki 3, and Assis. T. Yamaguchi 3. (Alphabetical order) 1 GSI, 2 Niigata Univ., 3 Saitama Univ.