Transcript Document

In-Beam Observables
Rauno Julin
Department of Physics
University of Jyväskylä
JYFL
Finland
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p
In - Beam
γ
α
n
p
γ
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Combination of In-Beam and Delayed Events
Focal plane
Detectors

Ge Array




prompt
events
= In-Beam
Data Readout
tagged with
delayed events
, p, β,
… e−, 
Best resolution in gamma-ray
spectroscopy
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Example: In-beam probing of Proton-Drip Line and SHE nuclei
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
Pb
Sn
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level energies, transition
multipolarities, spins, parities
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Yrast vs. non-Yrast
Close to the valley of stability:
All known energy levels in 116Sn
Far from stability:
Only a very limited set of levels close to the yrast line can be seen
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Example: in-beam spectroscopy at the extreme - 180Pb
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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Energy-level systematics:
Pb - isotopes
Level systematics of even-A Pb nuclei
Spherical
Oblate
Prolate
Prolate
Oblate
Spherical
180Pb
186Pb
104
N = 104
 Verification of
shape coexistence
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Energy-level systematics vs. Ground - state radia
Spherical 0p-0h
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+
T = 1 band
2+
66Se
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4+
6+
TED=Triple Energy Differences
TED =
Ex(Tz= -1) + Ex(Tz= +1) - 2 Ex(Tz= 0)
V = vpp + vnn - 2vpn
Charge independence
One-body terms cancel out
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Isospin non-conserving contribution is needed !
moment of inertia
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Basics
Kinematical moment of inertia
Dynamical moment of inertia
= arithmetical average of
over
Quantal system
Measured
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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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Example:
Nobelium region
J(1)  no Z = 104 shell gap
Why are 254No and 256Rf
almost identical ?
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Calculations
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Example:
Coexisting shapes in light Pb region
Rigid:
J(1) ~ 1 + 0.3β
Hydrodynamical:
J(1) ~ β2
→
Need B(E2) , Qt
J(1)(rig) = 110
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Subtracting a reference  details
Alignments:
180Pb
behaves
like 188Pb
→
Mixing with
oblate structures
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Subtracting a reference  details
Alignments near N =104:
Open symbols – Hg’s
Filled 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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In-beam lifetime measuremets
• Recoil distance Doppler-shift (RDDS)
lifetime measurements (plunger).
• Combined with selective recoil-decay
tagging method.
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Example: Lifetimes for shape coexisting levels in light Pb’s and Po’s
... for
194Po 196Po
186Pb
and 188Pb
│Qt │
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 ?
J(1)
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Exp vs. Theory
Beyond-mean-field calculations by M. Bender et al.
vs. the exp. data
Theor.
Exp
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Example: Collectivity of the intruder bands in light Pt, Hg and Pb nuclei
J(1) identical for prolate intruder bands in N ~ 104
Pt, Hg and Pb ⇒ identical collectivity (Qt)?
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Collectivity of the intruder bands in light Pt, Hg and Pb nuclei
|Qt| (eb)
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11
10
9
8
7
6
5
4
3
2
1
0
187
182
180
175
Pt
21/2
+
25/2
+
+
2
+
4
+
6
17/2
Hg
Au
+
178
Hg
10
8 ,10
+
4
+
4
+
6
4
+
6
+
+
+
29/2
+
25/2
+
21/2
+
+
2
2
+
prolate
194
8
17/2
Po
Po
+
+
2
+
4
oblate
Prolate - Oblate
196
Po
195
+
Prolate - Prolate
Oblate - Oblate
Pb
+
6 ,8
+
186
Tl
6++
4
17/2
+
2
+
+
2
+
Prolate - Spherical
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80
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Proton Number
Is the collectivity really decreasing
with decreasing Z ?
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Example: Experimental difficulties
Testing the simple seniority picture:
B(E2)-value systematics, N=122
2 8+
2 6+
2 4+
Δν=0
2 2+
Δν=2
0 0+
ν
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
Scale !!
Pt Hg
Why
the smooth
behaviour
at N = 104 ?
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Other mass filters needed to see the deviations
Hg isotopes
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Comment
Interpretation of E0 transition rates
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Example: 2neutron-2 hole intruders on the island of inversion
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 ?
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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)
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