Observation of Bound-State

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Observation of Bound-State ß Decayof Fully
Ionized 207 Tl at the FRS-ESR

• 9th Feb. 2004 / Ryo Koyama
• Masters Program in Fundamental Science of
  Matter,
• Graduate School of Science and Technology,
  Niigata University

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• ß decay for neutral/bare atom

Neutral atom
Bare atom
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Goal of present study

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

• II. Evaluate the beam purity of 207Tl81
• establish the experimental technique using
  secondary beam, cf 163Dy 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 ßb
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 ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 2
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• Outline of experimental method

Accelerator facility at GSI Gesellschaft für
Schwerionenforschung, Darmstadt, Germany
9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 3
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Separation in the FRagment Separator (FRS)
Particle identification by B?-?E - B? 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 ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 4
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• Beam cooling in the Experimental Storage Ring
  (ESR)

Injection from SIS / FRS
ESR

• Stochastic
• pre-cooling

? Reduce dP/P down to ?10-3

• Electron
• cooling

Ion beam
? Reduce dP/P down to ?10-6
9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 5
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• Schottky Mass Spectrometry (SMS)

frev v/C
B??m/q?v
?(Tl) gt ?(Pb) ? C(Tl) gt C(Pb) ? frev(Tl) lt
frev(Pb)
9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 6
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• Time dependent decrease/growth of Tl/Pb peak

consists of 50 freq. spectra
9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 7
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• ?2 fitting to the decay/growth curve of Tl/Pb

• NTl(t) NTl(0)exp(-?tott)

9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 8
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• Comparison with theoretical calculation

TC theoretical calculation WMweighted mean
standard deviation
Successfully observed ßb decay of fully ionized
207Tl !
9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 9
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Purity of injected 207Tl81 beam
? Purity of nearly 99 was achieved !
9th Feb. 2004 / R. Koyama - Observation of
Bound-state ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 10
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• Improved beam-cooling time

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 ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 11
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• Summary and future prospects

• We successfully observed bound-state ß- 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 ß- Decay of Fully Ionized 207Tl at
the FRS-ESR P. 12
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• 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.