1 / 14

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

This study focuses on observing the bound-state β decay of fully ionized 207Tl, exploring experimental methods like beam cooling and mass spectrometry. Results and future prospects are discussed. The goal is to measure decay rates and compare them with theoretical calculations, enhancing understanding of this decay process.

bgoodman
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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.

More Related