Atomic beam method for fragmentation-based radioactive beams Tokyo - - PowerPoint PPT Presentation

Atomic beam method for fragmentation-based radioactive beams

Tokyo Institute of Technology RIKEN

• H. Miyoshi, K. Asahi, K. Shimada, A. Yoshimi, H. Ueno, D. Kameda,
• H. Watanabe, K. Sakai, J. Murata, T. Haseyama, G. Kato, S. Emori,
• G. Kijima, M. Tsukui, Y. Kobayashi, H. Ogawa and W. –D. Schmidt-Ott

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Motivation

・

Searching for mechanism of nuclear structures

precise measurements of nuclear electromagnetic moments in a wide range

・

Atomic dynamics of surface and interface material

β-NMR technique、γ-PAC method、 Mossbauer spectroscopy

Atomic dynamics of surface and interface material.

Requirements : Various particles, Low energy, High spin polarization …

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Atomic beam method applied PF products

Principles of the method

• i. Stopping of RNB atoms in a gas cell
• ii. atomic spin selection by a field gradient
• iii. rf transition between two levels
• iv. second spin selection by a field gradient
• v. detection of the arrival at F by β, γ, or other activities

D F

"A" Magnet (6-pole) "C" Magnet (dipole) "B" Magnet (quadrupole)

RF Coil

“non- flipped” “flipped” “low-field seekers” “high-field seekers” (Counter)

Cyclotron Projectile Fragmentation Separator Stopping & drifting gas cell

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Spin Selection

C RF

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RF transition

factor g electoric factor g nuclear field magnetic externel constant n interactio hyperfine dipole magnetic

: : : :

J I

g g H a

Ｆ＝１ Ｆ＝２

) ( ) ( ) ( H I H J J I ⋅ + ⋅ + ⋅ = µ µ

I J

g g ha Η

Breit-Rabi formula for I=1/2, J=3/2

ν µ ν ν µ ν ∆ − = = ∆ + ∆ + = ∆ h H g g X a X Xm m h H g h m F E

I J F F J F

/ ) ( and | | 2 where , ) 1 ( 2 1 ) / ( 8 1 / ) , (

2 / 1 2

m I J F = I + J B0

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J I I N I J B J

m Am Bm g Bm g E + − − = µ µ

f

E

effect ) ( Zeeman weak B

effect ) ( Back Paschen strong B −

1 = F = F

First Step Second Step

ν h

RF Generator Static Field

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We calculated distribution of the magnetic field by using OPERA code

Sextupole magnet

B(pole tip) = 1.3 T Distribution of magnetic field

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Comparison of the data with calculation

We constructed the sextupole magnet and measured the distribution of magnetic field. We compare the measurement data to the OPERA code calculation. The measurement data consistent with the result of calculation. Measurement part

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Example) Ａ＝１２ Flight velocity = 500 m/s

’Transmission #+’10’cm’

20 40 60 80 100 120

• 3
• 2
• 1

1 2 3

position (cm) count

SPIN(1/2-) SPIN(1/2+)

Focus point @ 10cm behind 6pole magnet

The simulation of flight position through the sextupole magnet is shown in right figure. We assume that the center velocity is 500 m/s. The result shows that the particles which have specific electronic spin can be focused. mJ=-1/2 mJ=+1/2 Requirement: Low energy (< 1000 m/s) FWHM = 13 mm

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~ 1200 Torr ~ 3 Torr < 10-4 Torr 600 l/s 3000 l/s 3000 l/s 3000 l/s

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RI Stopping and Extraction system

RI RI-

• Stopping Chamber

Stopping Chamber Drift Drift-

• Efficiency

Efficiency RI RI-

• Separating Chamber

Separating Chamber Extraction Extraction-

• Efficiency

Efficiency Nozzle Nozzle Electrodes Electrodes Electrodes Electrodes Catcher Catcher

Beam Beam

10 cm

( -900 V ) ( -100 V ) ( -200 V ) TMP He: 600 Torr

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Production Target (9Be, 3.0mm) Primary Beam:

40Ar(95.0 MeV/u)

Secondary Beam:

31Al(>104 cps @F2)

Degrader@F1 for 31Al #3(Al, 444.0 mg/cm2) ΔE vs. TOF spectrum@Holly Degrader@F1 for 34P #1(30Al, 221.1mg/cm2) Secondary Beam:

34P(>105 cps @F2)

τ(34P)= 17.9 sec Qβ= 5.4 MeV

TEST Experiment for RI extraction

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Measurement of the Extraction-Efficiency

Nozzle 0.5 mm i.d.

Beam Momentum ±1.25% Catcher Electrodes 6.5 V/cm 650 V/cm 31 V/cm

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Extraction-Efficiency

Extraction-Efficiency ηext= ∆N/(Ωε)calc Ntotal =(3.87±1.12)x10-4 Position of the Catcher = -6.4 cm ∆N = 12 counts Ntotal =3.10✕106 counts

Center -6.3cm

For improving efficiency, 1: removing impurities ⇔ neutralization 2: make larger nozzle ⇔ extraction efficiency 3: use heavier mass stopping rare gas (Ne, Ar) ⇔ stopping efficiency

Goal : >10-2

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Summary

We are developing device which generate

“low-energy polarized RI Atomic beam”.

The device will be available for measurement of electromagnetic

moment and material physics and … etc.

We are now testing the RI stopping and extraction system.