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In-Beam ObservablesRauno Julin

Department of Physics University of Jyväskylä

JYFLFinland

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In - Beamγ

n

p

p

α

γ

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, p, β, … e−,

promptevents= In-Beam

delayed events

tagged with

Ge ArrayFocal planeDetectors

SeparatorBeam

Data Readout

Combination of In-Beam and Delayed Events

Best resolution in gamma-ray spectroscopy

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Sn

Pb

very neutron deficient heavy nuclei can be produced via fusion evaporation reactions cross-sections down to 1 nb short-living alpha or proton emitters → tagging methods

Nb

Example: In-beam probing of Proton-Drip Line and SHE nuclei

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level energies, transition multipolarities, spins, parities

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Yrast vs. non-Yrast

All known energy levels in 116Sn

Only a very limited set of levels close to the yrast line can be seen

Close to the valley of stability:

Far from stability:

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Example: in-beam spectroscopy at the extreme - 180Pb

4+ → 2

+

6+ →

4+

8+ →

6+

2+ → 0

+

α-α tagged singles in-beam γ-ray spectrum

92Mo(90Zr,2n)180Pb, 10 nanobarn

P. Rahkila et al. Phys. Rev. C 82 (2010) 011303(R)

Oblate Prolate

186Pb104

Spherical

Energy-level systematics: Pb - isotopes

Prolate

Oblate

Spherical

Level systematics of even-A Pb nuclei

N = 104180Pb8

Verification of shape coexistence

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Oblate 4p-2h Spherical 0p-0h

Prol

ate

6p-4

h

Energy-level systematics vs. Ground - state radia

Understanding of ground-state properties

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Odd-A nuclei: Information about orbitals and deformation

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Verification of prolate shape in 185Pb

Coupling of the i13/2 neutron ”hole” to the prolate core

Strongly coupled band

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Energy – level systematics: Coulomb-Energy Differences

A=66 is the heaviest triplet of T = 1 bands up to 6+

N = Z

TED =Ex(Tz= -1) + Ex(Tz= +1) - 2 Ex(Tz= 0)V = vpp + vnn - 2vpn

Charge independence One-body terms cancel out

TED=Triple Energy Differences

Isospin non-conserving contribution is needed !

T = 1 band66Se32

2+

4+

6+

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moment of inertia

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Kinematical moment of inertia

Dynamical moment of inertia

= arithmetical average of over

Quantal system

Measured

Basics

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J vs. deformation

Quadrupole deformed rigid rotor

not much dependent on deformation !

~ SD band in 152Dy

~ SD band in 193Bi

~ fission isomer in Pu

Fluid

strongly depends on deformation !

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J(1) no Z = 104 shell gap

Example: Nobelium region

Why are 254No and 256Rfalmost identical ?

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Calculations

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PROLATE

OBLATE

Rigid:J(1) ~ 1 + 0.3β

Hydrodynamical:J(1) ~ β2

→

Need B(E2) , Qt

J(1)(rig) = 110

Example: Coexisting shapes in light Pb region

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180 PbAlignments:

180Pb behaves like 188Pb→ Mixing with oblate structures

Subtracting a reference details

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Subtracting a reference details

Alignments near N =104:

Open symbols – Hg’sFilled symbols – Pb’s

Why Pb’s more scattered ?

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level lifetimes, transition rates, quadrupole moments, deformation

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Basics

Quadrupole deformed nucleus:

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• Recoil distance Doppler-shift (RDDS) lifetime measurements (plunger).

• Combined with selective recoil-decay tagging method.

In-beam lifetime measuremets

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│Qt │

J(1)

... for 194Po 196Po 186Pb and 188Pb

Example: Lifetimes for shape coexisting levels in light Pb’s and Po’s

Pb:│Qt │ → │β2 │ = 0.29(5) for the ”pure” prolate states

Po:│Qt │ → │β2 │ = 0.17(3)

for the oblate states- the ground state of 194Po is a pure

oblate 4p-2h state ?

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Beyond-mean-field calculations by M. Bender et al.vs. the exp. data

Theor.Theor.

Exp

Exp vs. Theory

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J(1) identical for prolate intruder bands in N ~ 104 Pt, Hg and Pb identical collectivity (⇒ Qt)?

Example: Collectivity of the intruder bands in light Pt, Hg and Pb nuclei

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oblate

prolate

Collectivity of the intruder bands in light Pt, Hg and Pb nuclei

Is the collectivity really decreasing with decreasing Z ?

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Δν=2

Δν=0

0+

2+

4+

6+

8+

0

2

2

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ν

Testing the simple seniority picture: B(E2)-value systematics, N=122

Example: Experimental difficulties

8+ is long living impossible to determine the lifetimes of the 6+, 4+ and 2+ members of the multiplet

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Comment

Mass systematics vs. shape coexistence

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Two-neutron separation energy systematics

HgPt Why the smooth behaviour at N = 104 ?

Scale !!

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∆4

Other mass filters needed to see the deviations

Hg isotopes

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Comment

Interpretation of E0 transition rates

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Interpretation: Weak mixing ( 10/90) between the spherical 0+ state and the deformed 2neutron-2hole intruder 0+ state (ß = 0,27)

Comment :

= 8.7 × 10-3 is a small value for an E0 transition in light nuclei

Does it make sense to apply such a simple model for such a weak E0 ?

Example: 2neutron-2 hole intruders on the island of inversion

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Example: 2neutron-2 hole intruders on the island of inversion

The simple two-level mixing model:

!!

Simple shell-model:

”Single-particle” value: = 40 × 10-3 (A=44)

(= E0 connecting 50/50 mixed 0+ states involving 2 protons occupying orbitals from different oscillator shells )

E0’s involving neutron excitations :

(if no state-dependent monopole effective charge for neutrons)