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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
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