Simple Atom, Extreme Nucleus:

Laser Trapping and Probing of He-8

Zheng-Tian Lu

Argonne National Laboratory

University of Chicago

Funding: DOE, Office of Nuclear Physics

2

Å

e-

Ionization Energy of Helium Atom

Level 2 3S1

Calculation 1 152 842 741 ± 6 MHz

Experiment 1 152 842 743 MHz

Gordon Drake, Phys. Scripta (1999)

Helium Atom

fm

3

Quantum Monte Carlo Calculations of Light Nuclei

Pieper & Wiringa. Ann. Rev. Nucl. Part. Sci. (2001)

4

Halo Nuclei 6He and 8He

Isotope Half-life Spin Isospin Core + Valence

He-6 807 ms 0+ 1 + 2n

He-8 119 ms 0+ 2 + 4n

Borromean RingsBorromean Nucleus

4He

8He

6He

QuantumMonte Carlo calculation

Proton

Neutron

5

Hadronic Probe: Scattering of 6He & 8He Beams

3.0

2.5

2.0

1.5

1.0

Inte

ract

ion

Rad

ius

(fm

)

876543

Helium Mass Number A

Tanihata et al, Phys Lett (1985)LBNL

Alkhazov et al, Nucl Phys (2002)GSI

Elastic and inelastic collision: He on C, B Elastic collision: He on H, 700 MeV/u

Matter distribution, matter radii

18O9Be

6He12C

6He1H

6He

6

Atomic Energy Levels of Helium

23S1

11S0

389 nm

1083 nm

23P0,1,2

19.82 eV

33P0,1,2

He energy level diagram

100 ns

100 ns 1.6 MHz• Single photon kick 0.1 m/s

• Transition rate ~ 4 x 106 /s

• Acceleration ~ 4 x 105 m/s2

Cooling & Trapping at 1083 nm

• Single photon kick 0.3 m/s

• Doppler shift 400 kHz

Spectroscopy at 389 nm

A glow discharge He gas cell

7

Field (Volume) Shift

AA

FS rZe

222 )0(3

2

1 10 1001E-3

0.01

0.1

1

10

100

| Iso

tope

Shi

ft |,

GH

z

Atomic number, Z

Mass shift

Field

shift

rE

s

p

V ~ - 1/r

8

Laser Cooling and Trapping

Magneto-Optical Trap (MOT)• Cooling: Temperature~ 1 mK,

avoid Doppler shift / width

• Long observation time: 100 ms

• Spatial confinement: trap size < 1 mm

single atom sensitivity

• Selectivity: no isotopic / isobaric interference

Technical challenges:

Short lifetime, small samples (106 atoms/s available)

Metastable efficiency ~ 10-5

Precision requirement (~100 kHz)

9

8He @ GANIL by Antonio Villari et al.

2.15 3.15

1.85

0.75

1.65

5 m

Salle D213C

• He-8: 5 x 105 s-1

• He-6: 1 x 108 s-1

8He+

@ 20 keV

8Hethermal

Laser System

MOT

ECR Ion Source

Massseparator

20 keV H

e +

1 GeV, 400 pnA

10

Atom Trapping of 6He & 8He at GANIL

~1x108 6He+/s~5x105 8He+/s

PMT

Zeemanslower

MOTTransverse

cooling389 nm

1083 nm

Atom Trap Setup

RF -Discharge

Xe

Spectroscopy389 nm

23S1

11S0

2 3P2

3 3P2

Trap1083 nm

He level scheme

Capture efficiency1x10-7

Source6He ~ 5x107/s8He ~ 1x105/s

Trap6He ~ 5 /s8He ~ 1x10-2/s

0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

1.2

Pho

ton

coun

trat

e/ k

Hz

Time (s)

One trapped 6He atom

11

He-8 Trapped!

First He-8 AtomJune 15th 2007

t

f

-10 -8 -6 -4 -2 0 2 4 6 8 100

100

200

300

400

500

Cou

nts

per

Cha

nnel

Rel. Laser Frequency, MHz

-10 -8 -6 -4 -2 0 2 4 6 8 100

20

40

60

80

100

Cou

nts

per

Cha

nnel

Rel. Laser Frequency, MHz

50 kHz

6He

~30 6He atoms/s

110 kHz60 atoms

8He

~30 8He atoms/hr

12

0.4

0.5

0.6

0.7

0.8

0.9

-0.2

0.0

0.2

0.4

0.6

0.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

6,

4 -

4319

4, M

Hz

(b)

(a)

8,

4 -

6470

1, M

Hz

J = 0 J = 1 J = 2

(c)

6He8He

Fie

ld S

hift,

MH

z

J = 0 J = 1 J = 2

8He

6He

Isotope Shift and Field Shift : J - Dependence?

2 3S1

389

nm

3 3P0,1,2

J=2J=1

J=0

J=1

Wang 04Argonne

J=13 1P1

13

6He & 8He RMS Charge Radii

6He 8He

Field Shift, MHz -1.464(34) -1.026(63)

RMS RCH, fm 2.072(9) 1.961(16)

Total Uncertainty 0.4 % 0.9 %

- Statistical 0.1 % 0.6 %

- Trap Systematics 0.3 % 0.6 %

- Mass Systematics 0.1 % 0.0 %

- He-4: 1.681(4) fm 0.1 % 0.1 %

Mueller et al., PRL (2007)

+ Ryjkov et al., PRL (2008): He-8 mass

+ Sick PRC (2008): He-4 Charge Radius

Rp

rc

Rn

- SO - MEC

<RP2> = 0.766(12) fm2

<RN2> = -0.120(5) fm2

14

6He & 8He RMS Point Proton and Matter Radii

Wang et al., PRL (2004)Mueller et al., PRL (2007) 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

Nuclear Radii, fm

4He rms point-proton matter Experiment Theory

8He

6He

15

He-6 CollaborationP. Mueller, L.-B. Wang, K. Bailey, J.P. Greene, D. Henderson, R.J. Holt, R. Janssens, C.L. Jiang,

Z.-T. Lu, T.P. O’Conner, R.C. Pardo, K.E. Rehm, J.P. Schiffer, X.D. Tang - Physics, Argonne G. W. F. Drake - Univ of Windsor, Canada

He-8 CollaborationP. Mueller, K. Bailey, R. J. Holt, R. V. F. Janssens, Z.-T. Lu, T. P. O'Connor, I. Sulai - Physics, Argonne;

M.-G. Saint Laurent, J.-Ch. Thomas, A.C.C. Villari - GANIL, Caen, FranceG. W. F. Drake - Univ of Windsor, Canada L.-B. Wang – Los Alamos Lab