Observation of Bound-State β Decay of Fully Ionized 207 Tl at the FRS-ESR

1. --- OUTLINE --- • Introduction • What’s a bound-state β decay ( )? • Goal of present study • Experimental method • Production of fully ionized 207Tl beam • Beam cooling • Schottky mass spectrometry • Experimental results • Data analysis • Results • Summary • Summary and future prospects β b Observation of Bound-State β Decayof Fully Ionized 207 Tl at the FRS-ESR 9th Feb. 2004 / Ryo Koyama Master’s Program in Fundamental Science of Matter, Graduate School of Science and Technology, Niigata University

2. SIS-FRS-ESR EXPERIMENTS β decay: n → p + e + ν Continuous-state β- decay ( decay) Bound-state β- decay ( decay) β β c b remaining in a bound atomic state 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 1 Neutral atom Bare atom β decay for neutral/bare atom

3. SIS-FRS-ESR EXPERIMENTS Solar ν problem: SSM pred. >> obser. s-process chronometry ν + 205Tl0+ → 205Pb1+ + e- : Eth〜50keV • Most sensitive to the pp-neutrino • Transition probability is unknown 205Tl81+ → 205Pb81+ + ν: βb decay ⇔ βb decay has been totally overlooked ! →Measuring the βb decay rates gives directly the ν-capture cross section [4] →Precise determination of βb decay rates is required [3] [3] K. Yokoi et al., AA 145 (1985) 339, [4] M.S. Freedman et al., Science 193 (1976) 1117. Goal of present study • I. Observe the βb decay of 207Tl81+ … • derive the decay rates, and compare them with theoretical calculations • II. Evaluate the beam purity of 207Tl81+ … • establish the experimental technique usingsecondary beam, cf163Dy [1], 187Re [2] [1] M. Jung et al., PRL 69 (1992) 2164, [2] F. Bosch et al., PRL 77 (1996) 5190. • III. Evaluate the beam-cooling time ... • first application of stochastic pre-cooling prior to electron cooling → Apply the experimental technique to the βb decay experiment of 205Tl which has been postponed because of its toxicity, will be feasible • 205Pb/205Tl pair would be a • short-lived s-process chronometer 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 2

4. Outline of experimental method SIS-FRS-ESR EXPERIMENTS III. Acceleration up to 〜830 MeV/u IV. 208Pb + 9Be Projectile fragmentation I. Production of 208Pb II. Pre-acceleration up to 〜11 MeV/u V. Separation of 207Tl81+ using Bρ-ΔE-Bρ technique VII. Observation of βb decay by the Schottky mass spectrometry (SMS) VI. Electron cooling with stochastic pre- cooling Accelerator facility at GSI Gesellschaft für Schwerionenforschung, Darmstadt, Germany 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 3

5. SIS-FRS-ESR EXPERIMENTS Bρ∝m/q･v Bρ∝m/q･v ΔE∝(z/v)2 → v∝z/ΔE1/2 -- Result of “MOCADI [5]” simulation -- [5] N. Iwasa et al., NIM B 126 (1997) 284. Separation in the FRagment Separator (FRS) Particle identification by Bρ-ΔE - Bρ method 〜830 MeV/u 208Pb beam from SIS to ESR Slits Wedge degrader Cocktail beam 4015 mg/cm2 9Be target 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 4

6. Beam cooling in the Experimental Storage Ring (ESR) SIS-FRS-ESR EXPERIMENTS Injection from SIS / FRS ESR • Stochastic • pre-cooling → Reduce δP/P down to 〜10-3 • Electron • cooling Ion beam → Reduce δP/P down to 〜10-6 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 5

7. Schottky Mass Spectrometry (SMS) SIS-FRS-ESR EXPERIMENTS • B(Tl) = B(Pb) • q(Tl) = q(Pb) = 81 • v(Tl) = v(Pb) ← cooling • m(Tl) > m(Pb) Bρ∝m/q･v ････ Intensity(t) Observation time → Fourier transform Int.(t) → Int.(frev) Intensity ∝ Nq2 Intensity(frev) Frequency frev = v/C Bρ∝m/q･v ρ(Tl) > ρ(Pb) → C(Tl) > C(Pb) → frev(Tl) < frev(Pb) 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 6

8. Time dependent decrease/growth of Tl/Pb peak SIS-FRS-ESR EXPERIMENTS consists of 50 freq. spectra 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 7

9. χ2 fitting to the decay/growth curve of Tl/Pb SIS-FRS-ESR EXPERIMENTS = λ NTl(t) - λA.I.NPb(t) βb λtot = λ +λ +λA.I. βb βc dNPb(t) dt • NPb(t) = NTl(0){exp(-λA.I.t) • - exp(-λtott)} + NPb(0)exp(-λA.I.t) λtot - λA.I. λ λ βb βc λ → , , NTl(0), NPb(0) βb • NTl(t) = NTl(0)exp(-λtott) 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 8

10. Comparison with theoretical calculation SIS-FRS-ESR EXPERIMENTS • Individual value of or • is systematically small than • theoretical calculation [6] [6] K.Takahashi et al., NP A 404 (1983) 578. ⇔ • The ratio of / is in agreement • within an experimental uncertainty λ λ λ βc βc βc ⇒ λ λ λ βb βb βb • Some theoretical assumptions are • not good enough, to calculate • individual value of or ? • T1/2(βb+βc) = 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 Successfully observed βb decay of fully ionized 207Tl ! 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 9

11. SIS-FRS-ESR EXPERIMENTS NPb(0) Contamination ratio = x 100 [%] NTl(0) + NPb(0) Purity of injected 207Tl81+ beam → Purity of nearly 99% was achieved ! 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 10

12. Improved beam-cooling time SIS-FRS-ESR EXPERIMENTS → Nearly 90% reduction of the beam-cooling time compared to those at the previous experiments [8], where only the electron cooling was applied [8] T. Ohtsubo et al.,GSI Rep. 2001-1 (2001) 15. Stochastic pre-cooling + Electron cooling Electron cooling only Injection→ 〜9 sec 〜60 sec 10-8 Time after injection 10-9 10-10 FFT frequency [a. u.] 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 11

13. Summary and future prospects SIS-FRS-ESR EXPERIMENTS • Derived bound-to-continuum branching ratio λ /λ is in agreement • with theoretical one, within an experimental uncertainty. βb βc • 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. βb βc • We successfully observed bound-state β- decay of fully ionized 207Tl • via the projectile fragmentation at the FRS-ESR. • We succeeded to reduce the number of 207Pb81+ ions down to roughly 1%. • 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 205Tl which has been postponed, is now feasible. • 205Tl is expected to be available as an experimental probe for the study • on the s-process chronometry and/or solar neutrino problem. 9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 12

14. 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. Bosch1, Prof. H. Geissel1, Prof. G. Münzenberg1, Assis. T. Ohtsubo2, Prof. S. Ohya2, Dr. C. Scheidenberger1, Prof. T. Suzuki3, and Assis. T. Yamaguchi3. (Alphabetical order) 1GSI, 2Niigata Univ., 3Saitama Univ.