In-Beam Observables Rauno Julin Department of Physics University of Jyväskylä JYFL Finland
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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)
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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)