Nuclear gamma-ray spectroscopy and lasers

Dep. of Phys., Odaka Univ.Atsuko Odahara

1. Introduction of gamma-ray spectroscopystudy of nuclear structure by measuring γ-rays

2. Recent results by our group using RI beams

(1) Study of change of shell structure to collective mode in neutron-rich Mg nuclei using polarized Na beam

( produced by laser )at TRIUMF, Canada

(2) Study of nuclear shape change using isomers ( excited levels with T1/2>~nsec)

at RCNP, Osaka Univ.

1. Introduction of gamma-ray spectroscopystudy of nuclear structure by measuring γ-rays

2. Recent results by our group(1) Study of change of shell structure to collective mode

in neutron-rich Mg nuclei using polarized Na beam ( produced by laser )

at TRIUMF, Canada(2) Study of nuclear shape change

using isomers ( excited levels with T1/2>~nsec) at RCNP, Osaka Univ.

nuclear deformation, nuclear motion and so on …

We could not watch nuclei by our eyes. nucleus : 10-15 m atom : 10-10 m

mesoscopic system quantum many body systemnucleus ( proton + neutron ) 1 ~ hundreds of nucleons

nuclear chart

stable nucleiunstable nuclei drip linesneutron number

stable nuclei 262unstable nuclei observed one ~3000

prediction ~7000

28

2028

50

82

2 820 28

50

82

126

magic number 2, 8, 20, 28, 50, 82, 126 …

Study of nuclear structure(1) nuclear deformation

spherical prolate(cigar)

[ lemon ]

oblate(pancake)[ orange ]

Nuclei with number of proton and/or neutron

is magic number

Shape of many nuclei

Shape of small number

of nuclei

( ))(1),( 020 θβϕθ ′+=′′ YRR

β: deformation parameterβ < 0 β > 0

spheroid

Rotation of nuclei with prolate shapealong the rotation axisperpendicular to the symmetry axis

Study of nuclear structure(2) nuclear motion --- rotation

prolate(cigar)

[ lemon ]

super deformationlong : short axes = 2 : 1

[ shape of ball used by rugby football ]

beta vibration gamma vibration octupole vibration

Study of nuclear structure(3) nuclear motion --- vibration

By measuring γ rays, we can study nuclear shape, nuclear motion and so on.

γ1

γ2

γ3

γ4γ5

γ1

γ2

γ3γ4

γ1

γ2

γ3γ4

γ-ray energy

γ2

γ1

γ3

γ2γ1

γ3

γ1γ2

γ3

γ4γ5

γ-ra

y in

tens

ity

(1) Single-particle motion of shperical, oblate nuclei

(2) vibration of nuclei

(3) rotation of prolate nuclei

(1)

symmetry axix

rotationasis

Study of nuclear structureGamma-ray spectroscopy method

(2)

(3)γ-ray energy

γ-ray energy

γ-ra

y in

tens

ityγ-

ray

inte

nsity

γ-ray spectra level scheme

151Tb super deformed bandJ : moment of inertia

E(I)Eγ

level energy : E(I)=I(I+1)/2J

γ-ray energy : Eγ=4I+6difference of γ-ray energy :

∆Eγ=4 const.

level scheme

RIKEN Web Page

expected exotic nuclear shapes and rotations in high-spin region

super deformation( 2 : 1 )

pear shape

hyper deformation( 3 : 1 )

oblate super deformation

( 1 : 2 )

tetrahedral ( pyramid )

octahedral( diamond )

banana shape

J. of Mod. Phys. E16 (2007) 516

prot

on n

umbe

r

neutron number

stable nuclei

unstable nuclei

A

neutron skin

neutron skin

neutron halo

large deformation

clusternulei

exotic nuclear shapes in light nuclei

RIKEN HP

1. Introduction of gamma-ray spectroscopystudy of nuclear structure by measuring γ-rays

2. Recent results by our group using RI beams(1) Study of change of shell structure to collective mode

in neutron-rich Mg nuclei using polarized Na beam ( produced by laser )

at TRIUMF, Canada(2) Study of nuclear shape change

using isomers ( excited levels with T1/2>~nsec) at RCNP, Osaka Univ.

Shimoda group Department of Physics, Osaka University

Shimoda group

polarized RI beamstudy of nuclear structure of exotic nuclei

Study of Nuclear Structure using RI beam

11Be10Ben

neutron halo

disappearance of N=20 magic number

prolate deformation

TRIUMF ( Canada )

OSAKA beam line

Ge detector ball

RI beamstudy of nuclear structureof high-spin isomers

high-spin shape isomer in N=83 isotones

oblate deformation

Ge detector ballRCNP, Osaka Univ.

F0 F２

F１

RCNP RI beam line ( EN course )

1. Introduction of gamma-ray spectroscopystudy of nuclear structure by measuring γ-rays

2. Recent results by our group using RI beams(1) Study of change of shell structure to collective mode

in neutron-rich Mg nuclei using polarized Na beam ( produced by laser )

at TRIUMF, Canada(2) Study of nuclear shape change

using isomers ( excited levels with T1/2>~nsec) at RCNP, Osaka Univ.

Shimoda group Department of Physics, Osaka University

1. neutron halo in neutron-rich nucleus 11Bestudied by β delayed neutron decay using polarized 11Li RI beam

2. Disappearance of magic number N=20 in neutron-rich Mg isotopes studied by β delayed γ decay using neutron-rich polarized Na beam

Study of exotic nuclear structure in neutron-rich nuclei using polarized RI beam

TRIUMF Canada

neutron halo10Ben

N=20 magic number

spherical

prolate ?

close to 32Mg20

Beta-decay spectroscopy with spin-polarized radioactive nuclei

β-γ coincidenceβ-γ-γ coincidence

very effective method to assign spin-parity of daughter states

polarized

polarization

β-delayed decay spectroscopy

at TRIUMF, Canada

β-decay from a spin-polarized nucleus

β-decay angular distribution

A: asymmetry parameter of allowed β-decayP: polarization of the parent nucleus

θ

A=1P=1

decay intensity

A takes very different valuesdepending on the final state spin.

～0

initial final

+: β+

-: β-

xN0

xN0

P can be evaluated from AP value for a transition to the known spin state.

A → spin assignment

polarization

free from instrumental asymmetry

ε: detection efficiency spin reversed

xN0

xN0

β-ray detection

905 MHz

νlaser freq.

pumping the two ground-state hyperfine levels in order to achieve high polarization

D1673 nm

atom1/2

nucleus3/2

905 MHz EOM was used

polarized beamproduced by optical pumping

TRIUMF ISAC （ Isotope Separator / Accelerator)

ISAC-1

ISAC-2

Na beam

polarization

B~830 gauss

9 Ge detectors&

18 Plastic Scintillators

Scintillator telescope

β- and γ-raysGe

plastic scintillators (1.5 mm)

spin assignments of the levels in

28Mg

R-detectorPol.+

R-detectorPol.-

L-detectorPol.+

L-detectorPol.-

2389 keV γ-ray peaks (3862 1473) coincident with β-rays

AP = -0.25±0.01 A = -0.89±0.05 Iπ = 0+

selecting ground-state transition.

1+ → 0+ : A = -1.0 uncorrected for spin-relaxation

⇒ P = 0.283(5)AP = -0.283(5)

β-ray energy spectrum

Revised Decay Scheme of 28Na and New Levels in 28Mg

Revised Decay Scheme of 29Na and Spin-Parity Assignments of 29Mg Levels

(3/2-, 7/2-)(3/2-, 7/2-)

negative parity states

These two levels are associated with large log ftvalues.

Shell model calculations with sd shell configurations do not predict no more levels around 1.0 - 1.5 MeV region.

Experimental systematics of negative parity levels

Z = 12 N = 17

prediction by AMD calculations (Kimura)

N = 13 15 17 19 21

1d5/2

2s1/2

1d3/2

1f7/2

2p3/2

1f5/2

2p1/2

20

28

negative parity

positive parity

single-particlelevels

1. Introduction of gamma-ray spectroscopystudy of nuclear structure by measuring γ-rays

2. Recent results by our group using RI beams(1) Study of change of shell structure to collective mode

in neutron-rich Mg nuclei using polarized Na beam ( produced by laser )

at TRIUMF, Canada(2) Study of nuclear shape change

using isomers ( excited levels with T1/2>~nsec) at RCNP, Osaka Univ.

Shimoda group Department of Physics, Osaka University

Study of nuclear shape change using isomers

isomer : excited levels with T1/2> ~nsec(normally T1/2 ~ 10-12 sec )

Isomers are caused by the nuclear structures. Isomers are good probe to obtain information of large change of nuclear structure.

shape isomer : caused by the sudden shape change

We are studying high-spin shape isomers with oblate shape.

at RCNP, Osaka Univ.

oblate(pancake)[ orange ]

Exotic shape and/or motion are expected to be observed in high-spin states in nuclei.

(a)

(b)

isomer

Exc

itatio

n E

nerg

y [

MeV

]

Er15168

13/2+1.14010ns

0.5s27/2-2.586

7/2- 0

(61/2+, 65/2-)10.288

420ns

23.5s

odd [ν(f7/2h9/2i13/2)πh11/22]49/2+

odd-odd [ν(f7/2h9/2i13/2)π(h11/22d5/2)]27+

152Er : [ν(f7/2h9/2i13/2)π(h11/24)]61/2+

151Ho: [ν(f7/2h9/2i13/2)π(h11/23)]28-

High-spin shape isomersin N=83 isotones

oblateβ ~ - 0.19

oblate

spherical

Study of nuclear structure using fusion reaction

beam(heavy ion) target

compound nucleus

neutron

alpha

proton

high-energy γ rays( ~ 5 – 10 MeV)

low-energyγ rays( up to ~3 MeV)

ground state

High angular momentum can be produce in compound nuclei.

Study of nuclear structure of the coldest high-spin state for each angular momentum

angular momentum

exci

tatio

n en

ergy

yrast line

by using fusion reaction

high-energy γ rays( ~ 5 – 10 MeV)

low-energyγ rays( up to ~3 MeV)

We can study the coldest statefor each angular momentumin nuclei.

Exotic shape and/or motion are expected to be observed in high-spin states in nuclei.

45≦Z≦8245≦N≦130

neutron number

β-stability lineN-Z~0.006xA5/3

50 60 70 80 90 100 110 120 130

80

70

60

50

45

prot

on n

umbe

r

Nuclear Chart :Experimental maximum spins reported in NNDC

Development of RI beam for the experiment using fusion reaction

except for SD with spins which are not confirmed

by A. Takashima

N=83 isotones

high-spin shape isomers

17N RI beam

Gamma-ray spectroscopy at RCNP, Osaka University

EN beam line(secondary beam line)

east experimental hall

1. direct beam provided by the AVF cyclotron2. new ECR ion source for heavy ion beam

in-beam γ-ray experiment using fusion reactionheavy ion beam with proper beam energy

ring cyclotronAVF cyclotron

since 2005

EN beam line

Maximum rigidity 3.2 TmEnergy acceptance ∆E/E = 16 %Angular acceptance ∆θ = 40 mrad

∆φ = 28 mradPath length 16.8 m

T. Shimoda et al., NIM B70 (1992) 320.S. Mitsuoka et al., NIM A372 (1996) 489.

F0

F２

F１

D1 D2

Q1Q2

Q3Q4

Q5Q6

Q7

SX1 SX2

SX3

RCNP secondary beam line

Ge array :14 Ge + 6 BGOACStotal efficiency 1.2 % at 1.3 MeVDep. of Phys. & RCNP Osaka Univ.Dep. of Phys. Tohoku Univ.SUNY

Search for high-spin shape isomers in 142Pr using 17N RI beam fusion reaction

primary reaction : 9Be(18O,17N)10B 9.2 MeV/u, 0.8 pµAsecondary reaction : 130Te + 17N 4.3 MeV/u,

2x104 pps, ~60%

Gamma-rays correlated to the secondary fusion reactionwere selected by using the information

time difference between PPAC and Ge detectors.

F0

F２

F１D1 D2

Q1Q2Q3Q4

Q5Q6Q7

SX1 SX2

SX3

PPAC

59 83

Ge array EN beam line (RCNP secondary beam line)

time difference [ns](PPAC-Ge)

coun

ts

50ns±

low-energy RI beam ( <10 MeV/u) for fusion reaction

Gamma-Ray Correlating with 17N RI Beam (γ-Singles)

PPAC-Ge timedifference[ns]

±50ns

coun

ts

γ-ray energy [keV]

coun

ts★

★

★

141 P

r[27

2.7&

273.

7]

●

★

141 P

r[45

4.0]

142 P

r[26

8]

●

●

●

●

●●

●

●

●

●

●

●

●★

142 P

r[35

8]

●

●

★

142 P

r[50

9]14

1 Pr[

509.

7]

★

★

142 P

r[55

3]

142 P

r[45

2]

★14

2 Pr[

373]

★142 P

r[56

3]

correlating with 17N RI beam (time difference ±50 ns)

without time gate

Live time:86 h 40 min.● background★ fusion products

PPAC 130Te

Ge detectors

γ-rays

±50ns

γ-rays associated with isomer

γ-rays energy[keV]

coun

ts

300 400 500 600

100

50

0

200

100

0

★

★

★

★

★★

142 P

r[26

8]

142 P

r[29

5]

142 P

r[35

8]

142 P

r[50

9]

142 P

r[55

3]14

2 Pr[

563]

projection spectrum

(b)+20~+350 ns

We can newly observed the γ-rays associated with the isomer by using PPAC-Ge time difference.

level scheme with isomer

(a)

(b)

PPAC-Ge time difference[ns]

(a)±10ns

coun

ts

(b)+20~+350ns

(a)±10ns

(9+) 61ns

Summary

1. Nuclear structure ( various shapes, motions and so on ) can be studied based on the gamma-ray spectroscopy.

2. Recent results using RI beams

(1) Study of change of shell structure to collective mode in neutron-rich Mg nuclei using polarized Na beam

( produced by laser optical pumping)at TRIUMF, Canada

Nuclear structure of 28Mg16 and 29Mg17 was studied. Disappearance of N=20 magic number was discussed in 29Mg.

(2) Study of nuclear shape change using isomers ( excited levels with T1/2>~nsec)

EN beam line (secondary beam line) at RCNP, Osaka Univ.Study for high-spin states of 142Pr was performed by low-energy (<10MeV/u) RI beam induced fusion reaction.

TRIUMF Experiment S1114

Dec. 2007@TRIUMF

K. Tajiri, T. Shimoda, K. Kura, M. Kazato, M. Suga, A. Takashima,T. Masue, T. Hori, T. Suzuki, T. Fukuchi, A. Odahara, Y. HirayamaA,N. ImaiA, H. MiyatakeA, C.D.P. LevyB, M. PearsonB, K.P. JacksonB

Osaka Univ., KEKA,TRIUMFB

RCNP experiment

Dep. of Phys., Osaka Univ. A. Odahara, A. Takashima T. Shimoda, K. Tajiri, M. Kazato, M. Suga,Y. Kenmoku, Y. Ito, K. Yamaguchi, K. Kurata, J. Takatsu

RCNP, Osaka Univ. T. SuzukiRIKEN

H. Watanabe, S. Nishimura, Y. Gono, T. Fukuchi CNS, Univ. of Tokyo E. Ideguchi, S. GoJAEA Y. WakabayashiDep. of Phys., Kyushu Univ. T. MorikawaDep. of Phys. Univ. of Paris Sud C. Petrache& IPN, Orsay, FranceIPN Orsay, France D. Beaumel

Study of high-spin states in 142Prby RI beam induced fusion reaction