Structure evolution towards 78 Ni :

Structure evolution towards 78Ni : challenges in the interpretation of hard-won experimental data

solved by simple means

David Verney, IPN Orsay

FUSTIPEN Topical Meeting -- « Recent Advances in the Nuclear Shell Model » -- June 19-20, 2014, GANIL, Caen

• An introduction to the N=50 shell effect/evolution towards 78Ni

• How and why the subject was introduced in Orsay

• What we have learned ?Selection of results (from Orsay and elsewhere) :

collectivity and evidence of intruder states in the 78Ni region

Verney – IPN Orsay FUSTIPEN Topical Meeting –Caen June 19-20, 2014

• An introduction to the N=50 shell effect/evolution towards 78Ni


The 78Ni region in 2014: the final cut (?)

Age of the pionneers: mid 80’s

TRISTAN(Brookhaven)/OSIRIS(Studsvik)

“Is the region above 78Ni doubly magic ?”r-process consequences

Fogelberg, J.C. Hill, J.A. Winger and others

The final cut ? : ca 2014

RIKEN

direct study of 78Ni

By Kratz et al. PRC 38 (1988)

Waiting point nucleus at N=50 80Zn

« » very busy decade

dormance

Second golden age : ca 2004

Yrast (LNL,Euroball)/Coulomb exc. (ISOLDE,ORNL)

/Masses (JYFL,ISOLDE)/transfer (ORNL,ISOLDE)

/Radioactivity(ORNL,Orsay)“Is N=50 a good magic number?”

r-process + structure consequences


The persistence of N=50: the core-breaking states

32

p1/2

g9/2

d5/2

neutrons

50

O. Sorlin, M.G. Porquet

Prog. Part. Nucl. Phys. 61 (2008) 602

N=50 gap extrapolation → 78Ni =3.0(5) MeV

After a decade : no (serious) evidence was found for shell quenching down to Z=30 in the low energy data (radioactivity and coulomb excitations studies). But:


The question of the size of the gap at N=50: what masses sayusing data taken from AME2012[including Hakala et al. PRL101 052502 (2008)]

collective origintheoretically : Bender et al. Phys. Rev. C 78, 054312 (2008)

maximum influence of beyond mean-field correlations

D = S2n(52)-S2n(50)

extracted from

Bender et al. Phys. Rev. C 78, 054312 (2008)e

d 5/2 –

eg 9/

2 (M

eV)

Ni Zn Ge Se Kr Sr

Duflo Zuker gap PRC59 (1999) 90Zr =4,7 MeV

Duflo Zuker gap 78Ni =5,7 MeV

« standard »« graphical »

loca

l min

imum

at Z

=32

Zr

K. Heyde et al. Phys. Let. B176 (1986) NPA466 (1987) 189

« standard »

« graphical »


K. Sieja and F. Nowacki, Phys. Rev. C 85, 051301R (2012)

minimum in gap D

The question of the size of the gap at N=50: shell model


NPA466 (1987) 189

Z

Sn(Z,N)-Sn(Z,N+1)

Sn(Z,N)-Sn(Z,Nextr)

N N+1 N+3 N+5 N+7neutron number

(Koopmans theorem)

gap in the single particle levels

n

50ej’n

ejn

-ej’n= Sn(Z,N)

but Sn(Z,N+1) is not a good prescription for

for the evaluation of ejn

one has to estimate ej’n and ej n in the same nucleus

ejn—ej’n = Sn(Z,N) —Sn(Z,Nextr) then the good prescription becomes :

The question of the size of the gap at N=50: back to core-breaking states

p1/2

g9/2

d5/2

neutrons

50

K. Heyde et al. graphical methodNPA466 (1987) 189

There are more things than monopole effects in the red curve …


K. Sieja and F. Nowacki, Phys. Rev. C 85, 051301R (2012)

The question of the size of the gap at N=50: back to core-breaking states

Fusion-fission experiment accepted for AGATA@GANIL campaign (spokespersons G. Duchêne and G. De Angelis)search for core-breaking Yrast states in 80Zn


figures taken from Bender et al. Phys. Rev. C 78, 054312 (2008)

N=50 vs Z=50 situations


• How and why the subject was introduced in Orsay

(experimental context)


Zn81

Present limit of structure knowledge(at least few excited states are known)

hot plasma ionization(1 µA deuteron primary beam)O. Perru PhD – def. 10th December 2004Eur. Phys. J. A 28, 307 (2006)+PhD A. Etile CSNSM ongoing

surface ionization (2-4 µA electron primary beam)M. Lebois PhD – def. 23th September 2008PRC 80, 044308 (2009) B. Tastet PhD – def. 13th May 2011PRC 87, 054307 (2013)D. Testov PhD – def. 17th January 2014

laser ionization(10 µA electron primary beam)K. Kolos PhD – def. September 2012PRC 88, 047301 (2013)

Ga84Ga83Ga82 Ga85Ga80Ga79

Ge80Ge79 Ge81 Ge85 Ge86

As82

hot plasma ionization(1 µA deuteron primary beam)PRC 76 (2007) 054312

-decay spectroscopyat the PARRNe mass separator (Tandem/ALTO)

Zn82

And “spin-off” elsewhere: -LNL :Plunger + AGATA + PRISMA-RIKEN: EURICA, MINOS campaignsaccepted : GANIL Plunger + AGATA + VAMOS LoI: SPES, SPIRAL2 phase 2


Tandem building Institut de Physique Nucléaire Campus of the Paris Sud University Orsay (France)


ALTO=ISOL installation based on photo-fission (the first of its kind in the world)

PARRNe mass separator

e-LINAC 10 µA 50MeV

(former 1st section of the

CERN LEP injector)

TIS vault>~1.10^11 fissions/s

Target Ion-source ensemble

kicker - bender

secondary beam lines

POLAREXnuclear

orientation on line

identification station

BEDObeta decay

spectroscopy

and the only facility in France providing fission fragments as mass separated RIBs (prefiguring for a time SPIRAL2.2)


plastic scintilator

Large volume Ge detector(EUROGAM-1 French-UK loan pool)

Ge CLOVER (proto EXOGAM )

Mylar tape

beam

etotal(photo-peak 1.3MeV)~2%

T1/2 measurement: tape motion cyclingTriggerless DAQ 400ps resolution time stamping

time

decayion beam deviated

build upion collection

Detection setup and movable tape


β energy loss

Compton

collection point

Ge

GeGe

plastic scintillator

4π-β

Ge

ancilaryplastic

BGO

4p beta

BEDO : BEta Decay studies at OrsayStrategy for optimal detection Compact geometry (max γ efficiency)

γ background suppression

BGO crystals


BEDO : BEta Decay studies at Orsay construction completed – commissioning beam time in 2012

Anti-Compton belt

4 EXOGAM small prototypesSource-cap distance = 5 cmevaluated e g (1 MeV) = 3-4 % (previous system 1-2%)

sensitivity 0.1 pps

up to 5 Ge detectors

6 plastic detectors

beam entrance


• What we have learned ?Selection of results,

collectivity and evidence of intruder states in the 78Ni region


Zn81

surface ionizationB. Tastet PhD – def. 13th May 2011PRC 87, 054307 (2013)laser ionization(10 µA electron primary beam)K. Kolos PhD – def. September 2012PRC 88, 047301 (2013)D. Testov PhD – def. 17th January 2014



As82

Zn82

-decay spectroscopyaround the Z=32 “curiosity”


isomerism in the N=49 line

(3-5) Hoff & Fogelberg NPA368 (1981)

8+6+

4+

2+

0+

(ng9/2-2)8+ seniority isomer

populated in DIC●Makishima et al PRC 59 (1999)●Podolyak et al Int. J. Mod phys E 13 (2004)●H. Mach et al J. Phys. G 31 (2005)

→ T1/2=2.95(6) ns

existence of second beta decaying state with I~7 suspected

ISOLDE experiment, laser spectroscopy : two long lived states in 80Ga I=3 and I=6 (negative parity from shell model)B. Cheal et al., PRC 82 (2010) 051302R


Study of 80Ga→80Ge beta decayhi

ts p

er 0

.5 k

eV

Energy (keV)


etc…Over the 75 γ-rays previously attributed to the 80Ga decay, the decay time of 67 individual β-delayed γ-activities were measured

the apparent half life of 30 levels could be determined

Study of 80Ga→80Ge beta decay


measured half-life in seconds

T1/2=1.6870.011s Singh Nuclear Data sheets 105 (2005) 223

apparent half-life of the 80Ge levels

longer lived

shorter livedHoff & Fogelberg 235U

ALTO

238 U



80Galonger

shorter

80Ge

lA (apparent half life)

lL

longer lived state contribution

shorter lived state contribution

levels of 80Ge

lS

1 0,8 0,6 0,4 0,2 0

lF (indirect feeding apparent half life)



80Galonger

shorter

T1/2= 1.90.1 s

T1/2= 1.30.2 s3―

6―



M. Honma et al., Phys. Rev. C 80, 064323 (2009)

B.A. Brown private communication, as first used in D. V. et al. Phys. Rev. C 76, 054312 (2007)

JUN45 JJ4B

multipletsclose to the 0(6) limit of IBM


Kumar model-independent n-body moments

[Kumar PRL28, 249 (1972)]

intrinsic shapes of SM eigenstates

JUN45 JJ4B

shell model calculations and transcription into intrinsic shapes


microscopic origin of the collective features

JUN45 JJ4B

f5/2

p3/2

p1/2

g9/2

p n

f5/2

p3/2

p1/2

g9/2

p n

collective gamma-soft configurations

f5/2

p3/2

p1/2

g9/2

p n

non-collectivequasi-particle like

configurations

Dℓ=2

quadrupole components of the interaction

pairing components of the interaction

►the energy proximity of f5/2 and p orbits (Dℓ=2) seems to be the key ingredient

energy separation between f5/2 and p3/2 in 79Cu :~1 MeV in JUN45 390 keV in JJ4B


Triaxiality at Z=32


76Ge

0+2 ?

Triaxiality at Z=32 and possible intruder 2p-2h 0+ states at N=48

“triaxial features” evolution of the 0+2 state energy


80Ge 80Ge

from M. Honma et al., Phys. Rev. C 80, 064323 (2009)


Zn81

laser ionization(10 µA electron primary beam)K. Kolos PhD – def. September 2012PRC 88, 047301 (2013)



As82

Zn82

-decay spectroscopyaround the Z=32 “curiosity”


Lebois et al.

Kolos et al.

Study of 84Ga5384Ge52 decay


(0—,1—)

Study of 84Ga5384Ge52 decay


84Ga5384Ge52 : addressing the collectivity development beyond N=50

0 0+

2+710

1744 4+

6+3095

1542 22+

1934 02+

2838 23+

HFB-5DCH Gogny D1S Delaroche et al. Bruyères-le-Châtel, available online, S. Hilaire M. Girod


0 0+

2+769

1584 4+

6+2900

1530 22+

42+21302002 31+

2812 51+

1768 02+

2150 24+

2603 43+

1873 23+

2360 32+

346

370

405

269

166

229231

599

77

137

145

0 0+

2+

(1+,2+)

(0+,1+,2+)

3502 (1+,2+)

EXP

2228

1389

624

JJ4B(proton-proton)+Sieja et al PRC 79, 064310 (2009)

g (°)

b =

0 0+

2+710

1744 4+

6+3095

1542 22+

1934 02+

2838 23+

HFB-5DCH Gogny D1S


A bit deeper into the problem of intruder states: odd isotones N=49

• What we have learned ?Selection of resultscollectivity and evidence of intruder states in the 78Ni region


Zn81



As82

Zn82

PhD A. Etile (CSNSM Orsay) ongoingfirst data taken with the new -decay spectroscopy setup BEDO(BEDO commissioning)

odd-odd nuclei:- detailed spectroscopy: stopped beam experiments- -decay very selective as allowed GT transitions e-e→o-o practically exclusively 0+→1+

A bit deeper into the problem of intruder states: the case of the odd-odd N=49 isotones


By Kratz et al. PRC 38 (1988)

Waiting point nucleus at N=50 80Zn

By Winger et al. PRC 36 (1987)

« »

The anomalous occurrence of low lying 1+ states in the odd-odd N=49 isotone 80Ga → historically launched the problematic of a possible vanishing of the N=50 shell effect


Winger et al. PRC 36 (1987) Fig. taken from Kratz et al. PRC 38 (1988)

RPA calculations, with significant quadrupole deformation (ε2=0.26) produce naturally an enormous amount of 1+ states (2QP states, Nilsson labeled), which was found satisfactory (!)

in a similar study Winger et al removed the parenthesis only at much higher energy


In the observation of the beta decay of an even-even to an odd-odd nucleus : one cannot (in principle) “miss” the lowest 1+ states (only 0+→1+ beta transitions are allowed in n-rich nuclei)

Q window

Eidens et al (1970)

Hoff & Fogelberg (1981)

Winger et al(1987)

note the huge increase in the number of states populated by beta decay between 82As and 80Ga-- is it real ? is there an important structure effect at play ?


H. Gausemel et al., Phys. Rev. C 70, 037301 (2004)

3.4(9)

80(20)

1.6(5)

0.35(9)

B(%) log ft

5.7(2)

4.2(2)

5.3(2)

5.8(2)

3.5(

5)8.

50(6

)

1.45

(2)

<1<1

100(

3)

(0-,1-)

(0,1)

(0,1)

Study of 82Ge→82As beta decay

(Still a bit preliminary)


what are the proton-neutron configurations one can expect at low energy ?→ let’s start with the zero-order coupling

O-ν

even-even semi-magic core

O-O O-π

E-Eproton open shell(proton quasi-particles)

neutron closed shell(neutron holes and intruder states)

odd-proton N=50 nucleus(taken from experimental level scheme)

odd-neutron N=49 nucleus(taken from experimental level scheme)

odd-odd N=49 nucleus(we hope to describe)


Neutron statesOmnipresence of positive parity (intruder) statesFirst hinted at from transfer reaction data [e.g. Detorie et al PRC18 (1978)]First systematics proposed by Hoff & Fogelberg NPA 368 (1981)emphasized in Meyer et al. PRC 25 (1982) since then everybody has been quiet on the subject

1p-2h states2+ p1/2

-1 or f5/2-1,p3/2

-1 ?

78Zn(d,p) R. Orlandi et al. (REX-ISOLDE)79-80Cu -decay M. Niikura (EURICA RIKEN)


A. Pfeiffer et al. NPA 455 (1986) 381

Proton states


from beta-decayD.V. et al. PRC 76, 054312 (2007)

Proton states

5/2 assignment to ground state unambiguously confirmed from laser spectroscopy measurementsCheal et al PRL 104, 252502 (2010) N.B. We will know more soon:

79Cu has been populated in 80Zn(p,2p) reaction at RIKEN recently (PhD work in Orsay under the supervision of S. Franchoo)


0

500

1000

1500

2000

2500

3000

3500

4000

86Rb 84Br 82As 80Ga

Ener

gy (k

eV)

f5*p3(+)

f5*f5(+)

p3*p1(+)

p3*p3(+)

p3*f5(+)

p1*p1(+)

p1*p3(+)

g9*g9(+)

0

500

1000

1500

2000

2500

3000

3500

4000

86Rb 84Br 82As 80Ga

Ener

gy (k

eV)

f5*d5(-)

f5*d3(-)

p3*d5(-)

p3*s1(-)

p3*d3(-)

p1*s1(-)

p1*d3(-)

82As is the first N=49 isotone for which low-spin negative parity (0- and 1-) states appear below the first 1+ state

Unperturbed positions of the proton-neutron configurations in the odd-odd N=49 isotones

normal positive parity intruder negative parity


Include 2d5/2, 3s1/2, 2d3/2 on top of the fp-g valence space → very challenging for shell model, not yet available

→ what can be done ?

→ in a first approach, one can use a much less computationally demanding solution:core-particle coupling model

→ our job was facilitated and encouraged by :(1) The description of odd N=49 nuclei down to 85Kr, including 2d5/2, 3s1/2, 2d3/2 has already been

done: Kitching Z. Phys. 258 (1973) ; Bhattacharya & Basu J. Phys. G 5 (1979)

(2) Hoffmann-Pinther & Adams [NPA229 (1974)] have already treated the odd-odd case within the Thankappan-True [Phys. Rev. 137 (1965)] schematic approach

Core QP π QP ν C - π

C - ν

π-ν interactionexperimental values fit to the odd nucleistrength adjusted on

86Rb


experimental

coupled to 0+

coupled to 2+

in agreement with identifications made by Dawson et al. Phys. Rev. 181 (1969)


experimental

coupled to 0+

coupled to 2+

3.4(9)

80(20)

1.6(5)

0.35(9)

B(%) log ft

5.7(2)

4.2(2)

5.3(2)

5.8(2)

3.5(

5)8.

50(6

)

1.45

(2)

<1<1

100(

3)

(0-,1-)

(0,1)

(0,1)only states coupled to 2+

2+ core coupled states ?

(clearly) π p3/2 ν p1/2-1

intruder π f5/2 ν d5/2


Winger et al. PRC 36 (1987) Fig. taken from Kratz et al. PRC 38 (1988)

RPA calculations, with significant quadrupole deformation (ε2=0.26) produce naturally an enormous amount of 1+ states (2QP states, Nilsson labeled), which was found satisfactory (!)

in a similar study Winger et al removed the parenthesis only at much higher energy


The 78Ni region in 2014: the final cut (?)

Age of the pionneers: mid 80’s

TRISTAN(Brookhaven)/OSIRIS(Studsvik)

“Is the region above 78Ni doubly magic ?”r-process consequences

Fogelberg, J.C. Hill, J.A. Winger and others

Second golden age : ca 2004

Yrast (LNL+Euroball)/Coulomb exc. (ISOLDE,ORNL)

/Masses (JYFL+ISOLDE)/transfer (ORNL,ISOLDE)

/Radioactivity(ORNL+Orsay)“Is N=50 a good magic number?”

r-process + structure consequences

Third golden age : ca 2014

RIKEN + elsewhere

direct study of 78Ni + around

very busy decade

dormance

towards an even busier decade

Conclusions• the question of the gap minimum Z=32, its microscopic origin and general consequences : we have just scratched the subject

• rapid energy increase of the p1/2 hole states below Z=32 (N=40 gap)

• Below Z=32, even at low energy, there is no hope shell model calculations can do a good job without including some external orbits (obvious statement but cruel necessity for experimentalists’ interpretations)

importance of the triaxial degree of freedom

AND the intruder states


backup slides


90’s ending, beginning 2000’s, ISOL activity back at IPN: PARRNe

converter(C)

deuteron beam(1µA 26 MeV)

fast neutrons

1+

ionsource

FissionFragments

target (10^9 fissions/s)

238U

fission

mass separator

detection

from P.W.Lisowski et al, OECD/NEA Report NEANDC-305 'U' 1991 p.177

Thesis Nicolas PauwelsIPN Orsay

initially a R&D test bench for the SPIRAL2 project

« Production d’Atomes Radioactifs Riches en Neutrons »

it all began with…


exploratory photofission experiment at CERN

arrival of the LINAC cavity from decommissioned LEP injector

construction of the LINAC bunker

RF system

First e-beam extracted

UCx target on line with e-beam– production yields measurements

Commissioning : tests and radiation safety measurements

TIS vault

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

1999

1998

building of the low energy beam lines + laser ion source

2011

2012

2013

green light from French nuclear safety authorities

BEDO commissioning

first laser ionized RIB

83Ga -> 83Ge b-decay

81Zn -> 81Ga b-decay

84Ga -> 84Ge b-decay

initial idea of a R&D test bench for the SPIRAL2 project at the Orsay Tandem

INAUGURATION

ISOL available at TANDEM PARRNe mass-separator on line


BEDO

LINOlaser spectroscopy

POLAREX

TAS

TETRA

nuclear orientation on line (CSNSM)

Total Absorption Spectroscopy(Subatech Nantes, IFIC Valencia)

Pn measurements(IPN/FLNR)

The ISOL installation at ALTO short and medium term projects


first experimental hint of proton evolution towards 78Nialong the N=50 linevery temptative, preliminary etc

p3/2

f5/2

28 29 30 31 32 33 34 35 36 37 38 39 40 41

-25

-20

-15

-10

-5

0

exactly consistent withPfeiffer et al. NPA 455 (1986) 381who provided sp energies, QP energies and v2.

prot

on E

SPS

(MeV

)

Z (N=50)

g9/2p1/2 Fermi level

f7/2

allows to explain the Jp of 80Ga and 80mGaISOLDE experiment, laser spectroscopy : two long lived states in 80Ga J=3 and J=6B. Cheal et al., PRC 82 (2010) 051302

extrapolation

Ga As BrCu Rb

Page 58/Verney – IPN Orsay Shell Model as Unified View of Nuclear Structure – 8-10 Oct. 2012


0

1

2

3

4

5

6

7

8

f5p3p1g9

PRO

TON

SPE

(MeV

)

p3/2

f5/2

g9/2

p1/2

JW Lis JUN45 JJ4B

Ji et Wildenthal Phys. Rev. C 38, 2849 (1988)

A.F. Lisetskiy et alPhys. Rev. C 70, 044314 (2004)

M. Honma et alPhys. Rev. C 80, 064323 (2009)

A. Brown priv. com.used inVerney et al Phys. Rev. C 76, 054312 (2007)

may be useful for shell model calculations in the 78Ni region

fitted SPE

result from monopole migration (realistic N-N interactions)

Sieja & Nowacki Phys. Rev. C 81, 061303(R) (2010)

SN this work

Page 59/Verney – IPN Orsay Shell Model as Unified View of Nuclear Structure – 8-10 Oct. 2012


ng9/2np1/2

Z=37

Z=35

Z=33

Z=31

Z=29

N=49

78Ni

78Cu

80Ga

82As

84Br

86Rb

N=50

p3

f5 ●● ●● ●●●●● ○

p3

f5 ●● ●● ●●●

p3

f5 ●● ●● ●○

p3

f5 ●

○ ○○

p3

f5 ●● ●○ ○○

Z=38 88Sr

pp 3/

2p

f 5/2

90Zr

pp 1/

2p

g 9/2

nd5/2 ns1/2 nd3/2

np3/2

nf5/2 86Rb Dawson et al. Phys. Rev. 181 (1969)

2,3,4,5,6,7

3,4,5,6


ng9/2np1/2

Z=37

Z=35

Z=33

Z=31

Z=29

N=49

78Ni

78Cu

80Ga

82As

84Br

86Rb

N=50

pf5/2-1ng9/2

-1

pp3/2-1ng9/2

-1

pf5/2-1ng9/2

-1

pp3/2+1ng9/2

-1

pf5/2-1ng9/2

-1

pp3/2+1ng9/2

-1

pf5/2+1ng9/2

-1

pp3/2+1ng9/2

-1

pf5/2+1ng9/2

-1

pp3/2+1ng9/2

-1

p3

f5 ●● ●● ●●●●● ○

p3

f5 ●● ●● ●●●

p3

f5 ●● ●● ●○

p3

f5 ●

○ ○○

p3

f5 ●● ●○ ○○

p3/2 turns into particle character

f5/2 turns into particle character

Z=38 88Sr

pp 3/

2p

f 5/2

90Zr

pp 1/

2p

g 9/2

N=49

nd5/2 ns1/2 nd3/2

np3/2

nf5/2

Structure evolution towards 78 Ni :

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