Fe 54 E1andM1excitationsin and low ... Schwengner | Institut für Strahlenphysik | γγγγ-ray beam...

Text optional: Institutsname � Prof. Dr. Hans Mustermann � www.fzd.de � Mitglied der Leibniz-GemeinschaftRonald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

E1 and M1 excitations in 54Fe

and

low-energy M1 strength in open-shell Fe isotopes

Ronald Schwengner

Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

The bremsstrahlung facility at the electron accelerator ELBE

Accelerator parameters:

• Maximum electron energy:

≈ 18 MeV

• Maximum average current:

≈ 0.8 mA

• Micro-pulse rate:

13 MHz

• Micro-pulse length:

≈ 5 ps

R.S. et al., NIM A 555, 211 (2005)

1 m

Be window

dipole

dipole

dipole

radiator

steerer

quadrupoles

quadrupole

electron-beam dump

quartz windowbeam

hardener

collimator

polarisationmonitor

target

PbPE

door

Pb

photon-beamdump

Pb

HPGe detector

experimentalcave

acceleratorhall


Detector setup at γELBE


3γγγγ-ray beam parameters Values

Energy 1 – 100 MeV

Linear & circular polarization > 95%

Intensity with 5% ∆Eγ/Eγ > 107 γ/s

Electron Accelerator Facility180 MeV Linac pre-injector180 MeV – 1.2 GeV Booster Injector250 MeV – 1.2 GeV Storage RingFELs: planar (linear pol.) and helical (circular pol.)

For more details see:http://www.tunl.duke.edu/higs/

• Highest intensity (γ-rays/s/keV) γ-ray beam in the world

• Produces γ-rays by Compton backscattering inside the optical cavity of a storage-ring FEL

• Produces both linearly and circularly polarized beams

Courtesy of C. Howell (TUNL)


Flux spectra at γELBE and HIγS

4000 6000 8000 10000Eγ (keV)

0

100

200

300

400

Φγ (

(eV

s)−

1 )

γELBE HIγS

Photon flux

γELBE: bremsstrahlung

HIγS: quasimononergetic,

polarized γ beams


Measurements at γELBE and HIγS

10000 10500 11000Eγ (keV)

100

101

102

103

Cou

nts

HIγS

Ee = 13.9 MeV

γELBE

Eγ = 10.6 MeV

E1

M1

Identification of multipolarities

from scattering of polarized

γ radiation at HIγS.

E1 radiation in vertical detectors

and M1 radiation in horizontal

detectors.


Measurement at γELBE

0 2 4 6 8 10 12 14Eγ (MeV)

1

10

100

1000

I s (eV

b)

54Fe28 Energy-integrated scattering

cross sections of levels in 54Fe

(J = 1 assumed)


Measurements at γELBE and HIγS

6 7 8 9 10 11 12Eγ (MeV)

10−2

10−1

100

B(M

1) (

µ N

2 )

54Fe28

6 7 8 9 10 11 12Eγ (MeV)

10−4

10−3

10−2

B(E

1) (

e2 fm2 )

54Fe28

Transitions with clear M1 or E1 assignments from the experiments at HIγS.


Experimental and calculated B(M1) values in 54Fe

6 7 8 9 10 11 12 13Eγ (MeV)

10−3

10−2

10−1

100

B(M

1) (

µ N

2 )

54Fe28 1

+ 0

+

5 6 7 8 9 10 11 12 13Eγ (MeV)

10−3

10−2

10−1

100

B(M

1) (

µ N

2 )

54Fe28 1

+ 0

+EXP CALC

Calculations using NuShellX.


Experimental and calculated B(M1) values in 54Fe

6 7 8 9 10 11 12 13Eγ (MeV)

10−3

10−2

10−1

100

B(M

1) (

µ N

2 )

54Fe28 1

+ 0

+

5 6 7 8 9 10 11 12 13Eγ (MeV)

10−3

10−2

10−1

100

B(M

1) (

µ N

2 )

54Fe28 1

+ 0

+EXP CALC

Calculations by K. Sieja.


Low-energy enhancement in 54Fe28

0 1 2 3 4 5 6 7 8Eγ (MeV)

0

0.02

0.04

0.06

B(M

1) (

µ N

2 )

π = +

54Fe

56Fe

Values in 56Fe as in

PRL 113, 252502 (2014),

but without lower limits of B(M1)

and without gates in Ex .


Shell-model calculations of M1 strength functions

0 2 4 6 8 10 12 14 16Eγ (MeV)

10−1

100

101

102

103

f 1 (1

0−9 M

eV−

3 )

94Mo

(3He,

3He’) data

shell modelM1

E1 + M1(γ,n) data

E1

)-3

(M

eV

M1

f

-910

-810

-710

Fe, Voinov et al. (2004) 56

)γαHe,3

(

Fe, Larsen et al. (2013) 56

)γ (p,p'

SM calc

Fe56

(a)

(MeV)γE0 1 2 3 4 5 6 7

)-3

(M

eV

M1

f-9

10

-810

-710

Fe57

(b)Fe, Voinov et al. (2004)

57)γHe'

3He,

3 (

Fe, Larsen et al. (2013/2014) 57

)γ (p,p'

SM calc

RITSSCHIL NuShellX

R.S., S. Frauendorf, A.C. Larsen

PRL 111, 232504 (2013)

B.A. Brown, A.C. Larsen

PRL 113, 252502 (2014)


Shell-model calculations for 60Fe34,64Fe38,

68Fe42

Code: NuShellX@MSU[B.A. Brown and W.D.M. Rae, Nucl. Data Sheets 120, 115 (2014)]

Model space: CA48PN with CA48MH1 Hamiltonian (48Ca core)[M. Hjorth-Jensen, T.T.S. Kuo, and E. Osnes, Phys. Rep. 261, 125 (1995)]

Orbits: π(0f(6−t)7/2 , 0ft

5/2, 1pt3/2, 1p

t1/2) ν(0ff 5

5/2, 1pp3

3/2, 1pp1

1/2, 0gg9

9/2)

Limitations of occupation numbers:

- t = 0 to 2.- f 5 = 2 to 6.- p3 = 0 to 4 for 60Fe and 2 to 4 for 64,68Fe.- p1 = 0 to 2 for all.- g9 = 0 to 2, 4, 6 for 60,64,68Fe, respectively.

Calculations: 40 levels of each spin from 0 to 10 and of each parity.

Transition strengths: eπ = 1.5 e, eν = 0.5 e; gs = 0.9 g frees


B(E2) values in Fe isotopes

Experimental and calculated reduced E2 transition strengthsof the 2+

1→ 0+

1transitions in 60,62,64,66,68Fe.

E (2+1) B(E2, 2+

1→ 0+

1) β2

(keV) (W.u.)EXP CALC EXP GLOB CALC CALC

60Fe34 824 772 13.6(14) 19.6 26.2 0.3162Fe36 877 544 14.7(18) 17.3 27.8 0.32

13.6(17)64Fe38 746 595 30.9+13.8

−7.2 19.1 26.8 0.3222.6(22)

66Fe40 574 568 21.0(21) 23.4 27.8 0.3268Fe42 522 616 24.2 25.4 0.31


Average M1 strengths in Fe isotopes

0 1 2 3 4 5 6Eγ (MeV)

0

0.02

0.04

0.06

B(M

1) (

µ N

2 )

π = +

64Fe

68Fe

60Fe

0 1 2 3 4 5 6Eγ (MeV)

0

0.02

0.04

0.06

0.08

B(M

1) (

µ N

2 )

π = −

64Fe

68Fe

60Fe

⇒ Enhancement of M1 strength toward very low transition energy.

⇒ Development of a bump around 3 MeV with increasing neutron number.

PRL 118, 092502 (2017)


Dipole strength functions in 151Sm and 153Sm

) -

3 S

F (

Me

Vγ

8−10

7−10

6−10

Sm, present exp.151

(p,d)

, n ), FilipescuγSm(150


), Kopecky, E1γSm(n,149

GDR

M1

nS

(MeV)γ

-ray energy Eγ0 2 4 6 8 10

) -

3 S

F (

MeV

γ

8−10

7−10

6−10

Sm, present exp.153

(p,d)



), Kopecky, E1γSm(n,149

GDR

M1

nS

(p,d) data:

A. Simon et al.

PRC 93, 034303 (2016)

⇒ First observation of upbend

and scissors resonance

in one nuclide

⇒ Strength in the scissors region

about twice of that found in

(γ, γ) experiments


Strength functions in 60Fe and 68Fe

0 1 2 3 4 5 6Eγ (MeV)

0

10

20

30

40

50

60

70f 1

(10−

9 MeV

−3 )

M1−60

Fe

M1−68

Fe

E1−RIPL

f 2 E

γ2 (10

−9 M

eV−

3 )

E2−60

Fe (x10)

E2−68

Fe (x10)

Dipole strength function

f1 = 16π/9 (hc)−3B(M1) ρ(Ex , J)

ρ(Ex , J) - level density

of the shell-model states,

includes π = +, π = −,

all spins from 0 to 10.

⇒ Strength in the scissors region

about three times that found in

(γ, γ) experiments.

PRL 118, 092502 (2017)

Eγ < 2 MeV 2 ≤ Eγ ≤ 5 MeV Sum60Fe34 5.67 3.52 9.1964Fe42 4.46 5.13 9.5968Fe42 3.98 6.63 10.61

B(M1)tot(µ2

N)


Absorption strength in 68Fe

0

0.2

0.4

0.6

0.8

1

B(M

1) (

µ N

2 )

68Fe

0+

gs 1+

0 1 2 3 4 5 6 7 8Eγ (MeV)

0

0.2

0.4

0.6

0.8

1

B(M

1) (

µ N

2 )

68Fe

0+

2 1+

0+

15

∑B(M1) (µ2

N) (2≤ Eγ ≤ 5 MeV)

0+1→ 1+ 0+

2→ 1+

60Fe34 0.66 1.9864Fe42 1.65 2.5968Fe42 1.74 3.45

⇒ Strength from excited statesabout two times that found in(γ, γ) experiments because ofmore strong M1 transitionsin the scissors region.

PRL 118, 092502 (2017)


M1 transitions in 68Fe

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9 10

Ex (

MeV

)

J

68Fe π = +

Transitions with B(M1) > 0.1µ2

N.

Line widths ∼ B(M1) values.

Ji = Jf , Jf ± 1, Eγ < 2 MeV:low-energy upbend

Ji = Jf ± 1, Eγ ≈ 3 MeV:scissors region

Ji = Jf + 1, Ex ∼ J(J + 1):shears bands


Nuclear rotation

electric (collective) rotation magnetic rotation

J

z

x

E2

M1

M1

M1

M1

M1

M1

M1

E2

E2

E2

E2

E2

M1

M1

M1

M1

M1

M1

E2

E2

E2

E2

B(E2) ∼ Q20 B(M1) ∼ µ2

⊥

E x =h2

2ΘJ(J + 1); E γ ∼ J


Predicted Appearance of magnetic rotation

0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

120

140

Neutron Number N

ProtonNumberZ

j"

2

j

0.25

0.15

28 50

82

126

28

50

82

64

64

20

20

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Magnetic rotation - “Shears bands”

S. Frauendorf, Rev. Mod. Phys. 73, 463 (2001).

Examples at A ≈ 80:

H. Schnare et al., PRL 82, 4408 (1999).

R.S. et al., PRC 65, 044326 (2002).

R.S. et al., PRC 66, 024310 (2002).

R.S. et al., PRC 80, 044305 (2009).


E2 transitions in 68Fe

0

5

10

0 1 2 3 4 5 6 7 8 9 10

Ex (

MeV

)

J

68Fe π = +

Line widths ∼ B(E2) values.

Ji = Jf , Jf ± 1:admixtures to dipole transitions

Ji = Jf + 2, Ex ≈ J(J + 1)/(2J ):collective bands


Average E2 strengths in 68Fe

0 1 2Eγ (MeV)

0

20

40

60

80

B(E

2) (

e2 fm4 )

68Fe, π = +

Ji = Jf + 2Ji = 2

34

5 6

7

810

9

Largest B(E2) valuesin rotational-like sequences:

Ex ≈ J(J + 1)/(2J )

Eγ ≈ (2J − 1)/J

J ≈ 12 MeV−1


Summary

◦ Photon-scattering experiments on 54Fe28 carried out at γELBE and HIγS. 30 prominent

E1 and 16 M1 transitions observed up to 11.5 MeV.

◦ Strength in the quasicontinuum in analysis. Additional experiment with bremsstrahlung

up to 7.5 MeV needed.

◦ Large-scale shell-model calculations performed for 60Fe34,64Fe38,

68Fe42.

Collective properties of yrast states are reproduced in the used model space.

◦ The low-energy M1 strength decreases with increasing neutron number and a bump in

the scissors region develops while the sum of the two stays nearly constant.

◦ The strength in the scissors region includes many transitions between excited states.

This explains the different strengths found in experiments using photoexcitation and

light-ion induced reactions.

⇒


Collaborators

Experiments at γELBE (HZDR): D. Bemmerer, R. Beyer, A.R. Junghans, T. Kogler,A. Wagner et al.

Experiments at HIγS (TUNL): M. Bhike, Krishichayan, W. Tornow,U. Gayer, H. Pai (U Darmstadt),V. Derya (U Koln)

Calculations: B.A. Brown (NSCL/MSU)S. Frauendorf (U Notre Dame)K. Sieja (IPHC/CNRS)

Fe 54 E1andM1excitationsin and low ... Schwengner | Institut für Strahlenphysik | γγγγ-ray beam...

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Transcript of Fe 54 E1andM1excitationsin and low ... Schwengner | Institut für Strahlenphysik | γγγγ-ray beam...