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

--- OUTLINE ---•Introduction

What’s a bound-state β decay ( )?Goal of present study

•Experimental methodProduction of fully ionized 207Tl beam

Beam coolingSchottky mass spectrometry•Experimental results

Data analysisResults

•SummarySummary and future prospects

βb

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 1

β decay for neutral/bare atomSIS-FRS-ESREXPERIMENTS

Neutral atom Bare 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 studySIS-FRS-ESREXPERIMENTS

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 2

II. Evaluate the beam purity of 207Tl81+ …•establish the experimental technique using secondary beam, cf 163Dy [1], 187Re [2]

III. Evaluate the beam-cooling time ...•first application of stochastic pre-cooling prior to electron cooling

I. Observe the βb decay of 207Tl81+ …•derive the decay rates, and compare them with theoretical calculations

→ Apply the experimental technique to the βb decay experiment of 205Tl 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) 5190.

ν + 205Tl0+ → 205Pb1+ + e- : Eth 〜 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) 1117.

→ 　 Measuring the βb decay rates givesdirectly the ν-capture cross section [4]

205Tl81+ → 205Pb81+ + ν : βb decay

Solar ν problem: SSM pred. >> obser.s-process chronometry

•205Pb/205Tl pair would be a short-lived s-process chronometer

→ 　 Precise determination of βb decay rates is required [3]

⇔ βb decay has been totally overlooked !

Accelerator facility at GSIGesellschaft 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

Outline of experimental methodSIS-FRS-ESREXPERIMENTS

I. Production of208Pb

II. Pre-accelerationup to 〜 11 MeV/u

III. Accelerationup to 〜 830 MeV/u

IV. 208Pb + 9BeProjectile fragmentation

V. Separation of 207Tl81+

using Bρ-ΔE-Bρtechnique

VI. Electron cooling withstochastic pre- cooling

VII. Observation of βb decayby the Schottky mass spectrometry (SMS)

Slits

Wedge degrader

〜 830 MeV/u

208Pb beamfrom SIS

4015 mg/cm2

9Be target

SIS-FRS-ESREXPERIMENTS

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 4

Separation in the FRagment Separator (FRS)

ΔE (∝ z/v)2

→ v∝z/ΔE1/2

Particle identification by Bρ-ΔE - Bρ method

to ESRBρ∝m/q ･ v

-- Result of “MOCADI [5]” simulation --[5] N. Iwasa et al., NIM B 126 (1997) 284.

Bρ∝m/q ･ v

Cocktailbeam

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 5

Beam cooling in the Experimental Storage Ring (ESR)SIS-FRS-ESREXPERIMENTS

•Stochasticpre-cooling

•Electroncooling

ESR Injection fromSIS / FRS

Ion beam

→ Reduce δP/P down to 〜 10-3

→ 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. 6

Schottky Mass Spectrometry (SMS)SIS-FRS-ESREXPERIMENTS

ρ(Tl) > ρ(Pb) → C(Tl) > C(Pb)→ frev(Tl) < frev(Pb)

frev = v/CBρ∝m/q ･ v

•B(Tl) = B(Pb)•q(Tl) = q(Pb) = 81•v(Tl) = v(Pb) ← cooling•m(Tl) > m(Pb)

Bρ∝m/q ･ v

････

Observation time →

Inte

nsi

ty(t

)

Fourier transformInt.(t) → Int.(frev)

Inte

nsity

(f rev)

Frequency

Intensity ∝ Nq2

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 7

Time dependent decrease/growth of Tl/Pb peakSIS-FRS-ESREXPERIMENTS

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. 8

χ2 fitting to the decay/growth curve of Tl/PbSIS-FRS-ESREXPERIMENTS

•NTl(t) = NTl(0)exp(-λtott)

βb βcλtot = λ +λ +λA.I.

, NTl(0), NPb(0)λβc,λβb

→

= λ NTl(t) - λA.I.NPb(t)βb

dNPb(t)dt

•NPb(t) = NTl(0){exp(-λA.I.t)

- exp(-λtott)} + NPb(0)exp(-λA.I.t)

λtot - λA.I.

βbλ

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 9

Comparison with theoretical calculationSIS-FRS-ESREXPERIMENTS

•The ratio of / is in agreementwithin an experimental uncertainty

λ βbλ βc

⇔

⇒

λ βbλ βc

•Some theoretical assumptions arenot good enough, to calculateindividual value of or ?

Successfully observedβb decay of fully ionized 207Tl !

•Individual value of or is systematically small than theoretical calculation [6]

λ βbλ βc

[6] K.Takahashi et al., NP A 404 (1983) 578.

•T1/2(βb+βc) = 256 s is 〜 10% shorterthan that of neutral atom 286 s [7]

[7] M.J. Martin et al., NDS 70 (1993) 315.

TC: theoretical calculationWM:weighted mean■:: standard deviation

Purity of injected 207Tl81+ beamSIS-FRS-ESREXPERIMENTS

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 10

Contamination ratio = NPb(0)

NTl(0) + NPb(0)x 100 [%]

→ Purity of nearly 99% was achieved !

[8] T. Ohtsubo et al.,GSI Rep. 2001-1 (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

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 11

Improved beam-cooling timeSIS-FRS-ESREXPERIMENTS

Electron coolingonly

Stochastic pre-cooling+

Electron cooling

〜 9 sec

〜 60 sec

Tim

e af

ter

inje

ctio

n

10-10

10-9

10-8

FFT frequency [a. u.]

Injection→

9th Feb. 2004 / R. Koyama - Observation of Bound-state β- Decay of Fully Ionized 207Tl at the FRS-ESR P. 12

Summary and future prospectsSIS-FRS-ESREXPERIMENTS

•We successfully observed bound-state β- decay of fully ionized 207Tlvia the projectile fragmentation at the FRS-ESR.

•We applied stochastic pre-cooling prior to electron cooling for the firsttime. We could reduce the beam-cooling time by about 90% compared tothose 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.

•We succeeded to reduce the number of 207Pb81+ 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.

βb βc

•Derived bound-to-continuum branching ratio λ /λ is in agreementwith theoretical one, within an experimental uncertainty.

βb βc

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.