Complementary Mechanisms in Nuclear Structure:...

Complementary Mechanisms in NuclearStructure: Isomers, Highly Excited States and

Giant Resonances

Jerzy DUDEK

UdS/IN2P3/CNRS, France and UMCS, Poland

Future of Low Energy Nuclear Physics in Polandand

Development of National Research Infrastructure

14 -15 January 2019Warsaw, Poland

Jerzy DUDEK, UdS and UMCS Complementary Mechanisms in Nuclear Structure

Question:

What are the complementary(to start with: possibly common) elements among:

Isomers? High-energy Excitations? Giant Resonances?

Answer(s):

May depend on who is asked

• Case 1: Isomers can exist at high energies, so are giant resonances(after Brink hypothesis) – so what the heck! Measure, & that’s it!

Triviality!

• Case 2: All above elements manifest the presence of symmetries,symmetry breaking, phase transitions, critical points & phenomena.

Fascinating!

Question:

Answer(s):

Triviality!

Fascinating!

Question:

Answer(s):

Triviality!

Fascinating!

Question:

Answer(s):

Triviality!

Fascinating!

Motto:

Symmetries Are the Tool of Choice

In Our Studies

of Stability of Atomic Nuclei

K-Isomers and Yrast -Traps

What are they?

... and what are the good reasons to study themin Poland in the years to come?

What are they?

Nuclear Spins Aligned With the Symmetry Axis

• We use the mean-field approachand the fact that in case of an ax-ial symmetry, say Oz -axis we have

[H, z ] = 0

• Consequently

H ϕν,mν = eν,mν ϕν,mν

z ϕν,mν = mν ϕν,mν

Projections of Angular Momenta

Single−NucleonAlignment

in the Presence of Axial SymmetryAre Conserved

[H, z ] = 0

• Consequently

[H, z ] = 0

• Consequently

Tilted Fermi Surface: Energy Minimisation at Given Spin

−3/2 1/2−1/2 3/2 5/2−5/2 7/2−7/2 9/2−9/2 11/2−11/2−13/2 13/2

For the particle-hole excited-states we obtain at the same time thetheoretical energy and theoretical spin:

E ∗ =∑p

ep,mp −∑h

eh,mhand I ≈ M∗ =

mp −∑h

−9/2 1/2−1/2 3/2−3/2 5/2−5/2 7/2−7/2 9/2 11/2−11/2−13/2 13/2

M=11/2 − (−7/2) = 9

For the particle hole excited states we obtain at the same time thetheoretical energy and theoretical spin:

E ∗ =∑p

ep,mp −∑h

mp −∑h

1/2−1/2 3/2−3/2−5/2 7/2−7/2 9/2−9/2 11/2−11/2−13/2 13/2

M=11/2 +

9/2 − (−

7/2 − 5/2) =

For the particle hole excited states we obtain at the same time thetheoretical energy and theoretical spin:

E ∗ =∑p

ep,mp −∑h

mp −∑h

Irregular Nature of p-h Excitations Generates Yrast Traps

Energy

TrapsYrast

npSpin = M + M

Y r a s t

L i n e

E ∗ =∑p

ep,mp −∑h

eh,mhand M∗ ≈ Spin =

mp −∑h

How Powerful the Idea Is – See Illustration 1

Spins & parities of all experimentally known isomers can be deduced from the diagrams:4.50 ns at Iπ = 21/2+, 26.8 ns at Iπ = 27/2−, 530 ns at Iπ = 49/2+. Ground state:Iπ = 7/2− has 38 h half-life. Maximum alignment neutron configurations lead toIπ = 9/2− and Iπ = 13/2+ states have lifetimes of 0.35 ps and 21.4 ns, respectively.

Iπ = 19/2− isomer, of 0.37 ns is given by [πd−25/2

]0 × [h211/2

]max6 × ν[f 1

7/2]7/2.

All these structures can be directly deduced from the presented diagrams.

[The lifetimes correspond to the contemporary values taken from Live Chart Table ofNuclides: https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html; theoreticalresults presented were first published over 30 years ago, ref. [?].]

• Yrast 147Gd sequence calculatedusing the realistic phenomenologicalWS-universal mean field approach.

• The energy of each state hasbeen minimised over several axial-symmetry deformation parameters.

• Somebody may ask:

How many parameters have beenfitted to obtain this result?

← 45/2-

Yrast Levels

64Gd83147

Expt. Calc.

← 45/2-

Yrast Levels

64Gd83147

Expt. Calc.E

← 45/2-

Yrast Levels

64Gd83147

Expt. Calc.E

← 45/2-

Yrast Levels

64Gd83147

Expt. Calc.E

Or: An attentive listener could say:

This quality of description can be a sign of a powerful modelling:

• Is this just the case of reproduction by fitting?

• Or rather a manifestation of predictive power?

In other words: How many parameters are fitted to spectra?

NONE – no parameter adjusted to the presented data;This is what is meant as Woods-Saxon Universal mean-field

Suppose We Give Ourselves the Means For Studying K-Isomers: Part I

What Do We LearnFrom Measuring K-Isomers?

• Establish areas of existence of axial symmetry, as opposed tonon-axiality, throughout the Periodic Table. But: Why some(Z,N)-combinations induce axial symmetry and others do not?

• The axial-symmetry nuclei may choose to rotate collectively

(~I ⊥ Osymmetry) − bands

as alternative to

(~I ‖ Osymmetry) − isomers

or both at the same shape at the same time (in competition).

Why? Which mechanisms cause this or that behaviour?

as alternative to

Suppose We Give Ourselves the Means For Studying K-Isomers: Part II

• K-isomers may live longer or even much longer comparedwith the related ground states → This allows extending theexperimental accessibility to the New Areas of Exotic Nuclei!

• The life-times of K-isomers vary dramatically over many theorders of magnitude providing precious information about:

– The configuration changes via decay: (np-nh) → (n’p-n’h)

– Signals of spontaneous axial-symmetry breaking [K-mixing]

• By the way: No serious tests of the mean-field theory arepossible without the cross-checking of the above information!

New Kind of Isomers

Isomers generated by the high-rank symmetries

Nickname: High-Rank Symmetries:

Tetrahedral and Octahedral Point-Group Symmetries

New Kind of Isomers

Nuclear Tetrahedral Shapes – 3D Examples

Illustrations below show the tetrahedral-symmetric surfaces at threeincreasing values of rank λ = 3 deformations α32: 0.1, 0.2 and 0.3

Figure: α32 ≡ t3 = 0.1 Figure: α32 ≡ t3 = 0.2 Figure: α32 ≡ t3 = 0.3

Observations:

There are infinitely many tetrahedral-symmetric surfaces

Nuclear ’pyramids’ do not resemble pyramids very much!

Tetrahedral Bands Are Not Like the Others!

g.s.b.

transtionswith NO E2

Tetrahedral band

Schematic Illustration

• The A1-representation sequence of spin-parity states forms a single parabola

A1 : 0+, 3−, 4+, 6+, 6−, 7−, 8+, 9+, 9−, 10+, 10−, 11−, 2 × 12+, 12−, · · ·

• There belong states of both parities and, in addition, they form doublets, triplets, etc.

Tetrahedral & Octahedral-Symmetry Signals: Experiment

Sm152 62 90

0 1 2 3 4 5 6 7 8 9 10 11 12Spin ~

Experimental Results [Td -vs.-Oh]

Symmetry Hypotheses:

Tetrahedral: Td

Octahedral: Oh

A1 → r.m.s.=80.5 keV

A1g → r.m.s.=1.6 keVA2u → r.m.s.=7.5 keV

9+ 11−

7−6+

Illustration of experimental results, cf. PHYS. REV. C 97, 021302(R) (2018).Curves represent the fit and are not meant ‘to guide the eye’. Markedly, point[Iπ = 0+], is a prediction by extrapolation - not an experimental datum.

Suppose We Give Ourselves the Means For Studying Tetrahedral Bands

What Do We LearnFrom Identifying High-Rank Symmetries?

• Exact high-rank symmetries imply Q1 = 0 and Q2=0 →

B(E1) = 0 and B(E2) = 0

• This implies presence of EI ∝ I (I + 1) sequences of excitedisomeric states – connected by neither E1 nor E2 transitions!

• We find parabolic bands of isomers – possibly waiting pointnuclei influencing the interpretation of astrophysical processes!

• Life-times of those states, not known today, may be primarilygiven by the E3-decay and/or β-decay→ therefore very long

B(E1) = 0 and B(E2) = 0

For more details about this type of isomers

cf. presentation by Irene Dedes

High Energy Excitations,

Giant Resonances

Jacobi and Poincare Shape Transitions

Jacobi Transitions - Mechanism of Criticality

• Consider an example of Jacobi shape transitions: 46Ti and 142Ba;

0.0 0.5 1.0 1.5 2.0-0.4

Ti24 Ti 46 22

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=24 E= 32.6

0.0 0.5 1.0 1.5 2.0-0.4

Ba86 Ba142 56

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=60 E= 31.1

0.0 0.5 1.0 1.5 2.0-0.4

Ti24 Ti 46 22

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=28 E= 42.9

0.0 0.5 1.0 1.5 2.0-0.4

Ba86 Ba142 56

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=70 E= 41.2

0.0 0.5 1.0 1.5 2.0-0.4

Ti24 Ti 46 22

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=28 E= 42.9

0.0 0.5 1.0 1.5 2.0-0.4

Ba86 Ba142 56

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=70 E= 41.2

0.0 0.5 1.0 1.5 2.0-0.4

Ti24 Ti 46 22

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=32 E= 53.0

0.0 0.5 1.0 1.5 2.0-0.4

Ba86 Ba142 56

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=80 E= 51.9

0.0 0.5 1.0 1.5 2.0-0.4

Ti24 Ti 46 22

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=32 E= 53.0

0.0 0.5 1.0 1.5 2.0-0.4

Ba86 Ba142 56

01234567891011121314151617181920212223

E [MeV]

!2 cos("+30°)

! 2sin

I=80 E= 51.9

Shape at β2 =0.6 Shape at β2 =0.9

The Physics of Large Amplitude Motion

Or: Nuclear Motion in the Vicinity of Critical Points

• Let us consider the nuclear motion for spins in the vicinity of thecritical (transition-) spin values [the Jacobi transitions to start with]

• The criticality consists in the fact that:

– Nuclear shapes change dramatically, cf. the previous illustrations

– The intrinsic occupancy of nucleonic orbitals changes dramatically

– And yet, the total potential energy varies by a couple of hundredsof keV only – “dramatic intrinsic changes” cost no energy

• Under these conditions deformations of the actual energy minimacarry no particular physics information ⇒⇒ are next to meaningless

• Consequently, one has to solve quantum mechanical problem of thenuclear collective motion, find the wave functions and the most prob-able deformations, root-mean-square deviations (σ-values), etc.

Posing the Problem of Large Amplitude Motion

• Despite the fact that model used here to parametrize the nuclearenergy is classical – the physical nuclear system is of course quantum

• The corresponding Schrodinger equation has a usual general from

[T + V (α)] Ψn(α) = En Ψn(α) with V (α)↔ VLSD(α)

• Knowing the solutions we can calculate the expected values αλµtaken as a measure of the most probable deformation and given by:

〈α2λµ〉 ≡

∫dαΨ∗

n(α)α2λµΨn(α) → αλµ =

√〈α2

λµ〉

• In this way we obtain two, different and non-equivalent realisationsof the description of physical deformations: static and dynamical:

(α20, α22)stat. →→ (α20, α22)dyn.

〈α2λµ〉 ≡

∫dαΨ∗

√〈α2

λµ〉

(α20, α22)stat. →→ (α20, α22)dyn.

〈α2λµ〉 ≡

∫dαΨ∗

√〈α2

λµ〉

(α20, α22)stat. →→ (α20, α22)dyn.

Shape Uncertainties During Jacobi Transitions

• Results of calculations∗) obtained by solving Schrodinger equation

0 10 20 30 40 50 60 70 80 90

L [ /h]

statdyn

0 10 20 30 40 50 60 70 80 90

L [ /h]

120Cdstatdyn

• To obtain the results above we have introduced dispersion coeffs.

σ20 ≡√〈α2

20〉 − 〈α20〉2 and σ22 ≡√〈α2

22〉 − 〈α22〉2

• Positions of the squares are given by√〈α2

20〉 and√〈α2

22〉. The barsrepresent the intervals of the size (±σ) as the quantitative estimates

∗)Collaboration with K. Mazurek and D. Rouvel

0 10 20 30 40 50 60 70 80 90

L [ /h]

statdyn

0 10 20 30 40 50 60 70 80 90

L [ /h]

120Cdstatdyn

σ20 ≡√〈α2

20〉 − 〈α20〉2 and σ22 ≡√〈α2

22〉 − 〈α22〉2

20〉 and√〈α2

0 10 20 30 40 50 60 70 80 90

L [ /h]

statdyn

0 10 20 30 40 50 60 70 80 90

L [ /h]

120Cdstatdyn

σ20 ≡√〈α2

20〉 − 〈α20〉2 and σ22 ≡√〈α2

22〉 − 〈α22〉2

20〉 and√〈α2

Determining the GDR Profile Gives Most Probable Shape

• Experiment vs. modelling with high-temperature thermal shape-fluctuations; Splitting of the GDR allows to deduce deformation

• Experimental results from A. Maj et al., Nucl. Phys. A731, 319 (2004)

Dramatic Shape Changes Cost Nearly No Energy

Suppose We Give Ourselves the Means For Studying Giant Resonances

What Do We LearnFrom the GDR Shape-Probability Profiles?

• By examining the Coriolis splitting of the GDR profiles welearn experimentally about shape evolution with spin and ex-citation energy as well as about the most probable shapes

• Establishing the critical spin values for the Jacobi shapetransitions we get instructed how to optimise the populationconditions for the hyper-deformed states an elusive subject todate

• From competition between Jacobi and Poincare shape tran-sitions we control the fission fragment mass distributions withincreasing spin – important nuclear structure information

Final Remarks about a Special Editionof Potential Interest

When discussing future of nuclear physics

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