Structure evolution towards 78 Ni :

1. Structure evolution towards 78Ni : challenges in the interpretation of hard-won experimental data solved by simple means David Verney, IPN Orsay • 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 FUSTIPEN Topical Meeting -- « RecentAdvances in the Nuclear Shell Model » -- June19-20, 2014, GANIL, Caen

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

3. The 78Ni region in 2014: the final cut (?) 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 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 dormance «  » Waiting point nucleus at N=50 80Zn very busy decade The final cut ? : ca 2014 RIKEN direct study of 78Ni By Kratz et al. PRC 38 (1988)

4. The persistence of N=50: the core-breaking states 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: d5/2 50 g9/2 p1/2 neutrons 32 O. Sorlin, M.G. Porquet Prog. Part. Nucl. Phys. 61 (2008) 602 N=50 gap extrapolation → 78Ni =3.0(5) MeV

5. The question of the size of the gap at N=50: what masses say using data taken from AME2012 [including Hakala et al. PRL101 052502 (2008)] collective origin theoretically : Bender et al. Phys. Rev. C 78, 054312 (2008) D = S2n(52)-S2n(50) DufloZuker gap 78Ni =5,7 MeV Duflo Zuker gap PRC59 (1999) 90Zr =4,7 MeV local minimum at Z=32 « graphical » «standard » ed5/2 – eg9/2 (MeV) extracted from Bender et al. Phys. Rev. C 78, 054312 (2008) K. Heyde et al. Phys. Let. B176 (1986) NPA466 (1987) 189 Zn Ge Ni Se Kr Sr Zr «standard » maximum influence of beyond mean-field correlations « graphical »

6. The question of the size of the gap at N=50: shell model K. Sieja and F. Nowacki, Phys. Rev. C 85, 051301R (2012) minimum in gap D

7. The question of the size of the gap at N=50: back to core-breaking states K. Heyde et al. graphical method NPA466 (1987) 189 d5/2 NPA466 (1987) 189 50 g9/2 Z p1/2 Sn(Z,N)-Sn(Z,N+1) neutrons Sn(Z,N)-Sn(Z,Nextr) N+5 N+7 N N+3 N+1 There are more things than monopole effects in the red curve … neutron number ejn -ej’n= Sn(Z,N) gap in the single particle levels 50 (Koopmans theorem) ej’n but Sn(Z,N+1) is not a good prescription for for the evaluation of ejn n one has to estimate ej’n and ejnin the same nucleus ejn—ej’n = Sn(Z,N) —Sn(Z,Nextr) then the good prescription becomes :

8. The question of the size of the gap at N=50: back to core-breaking states K. Sieja and F. Nowacki, Phys. Rev. C 85, 051301R (2012) Fusion-fission experiment accepted for AGATA@GANIL campaign (spokespersons G. Duchêne and G. De Angelis) search for core-breaking Yrast states in 80Zn

9. N=50 vs Z=50 situations figures taken from Bender et al. Phys. Rev. C 78, 054312 (2008)

10. • How and why the subject was introduced in Orsay (experimental context)

11. -decay spectroscopy at the PARRNe mass separator (Tandem/ALTO) hot plasma ionization (1 µA deuteron primary beam) O. Perru PhD – def. 10th December 2004 Eur. 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 2008 PRC 80, 044308 (2009) B. Tastet PhD – def. 13th May 2011 PRC 87, 054307 (2013) D. Testov PhD – def. 17th January 2014 laser ionization (10 µA electron primary beam) K. Kolos PhD – def. September 2012 PRC 88, 047301 (2013) Present limit of structure knowledge (at least few excited states are known) Ge85 Ge81 Ge79 Ga79 Ge86 As82 Ga82 Ga83 Ge80 Ga80 Zn81 Ga85 Ga84 Zn82 And “spin-off” elsewhere: -LNL :Plunger + AGATA + PRISMA -RIKEN: EURICA, MINOS campaigns accepted : GANIL Plunger + AGATA + VAMOS LoI: SPES, SPIRAL2 phase 2 hot plasma ionization (1 µA deuteron primary beam) PRC 76 (2007) 054312

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

13. ALTO=ISOL installation based on photo-fission (the first of its kind in the world) e-LINAC 10 µA 50MeV (former 1st section of the CERN LEP injector) and the only facility in France providing fission fragments as mass separated RIBs (prefiguring for a time SPIRAL2.2) BEDO beta decay spectroscopy secondary beam lines TIS vault >~1.10^11 fissions/s POLAREX nuclear orientation on line PARRNe mass separator Target Ion-source ensemble kicker - bender identification station

14. Detection setup and movable tape beam Mylar tape Large volume Ge detector (EUROGAM-1 French-UK loan pool) plastic scintilator Ge CLOVER (proto EXOGAM ) etotal(photo-peak1.3MeV)~2% T1/2 measurement: tape motion cycling Triggerless DAQ 400ps resolution time stamping time buildup ion collection decay ion beam deviated

15. BEDO : BEta Decay studies at Orsay Strategy for optimal detection Compact geometry (max γefficiency) γ background suppression BGO ancilary plastic 4π-β BGO crystals Ge Ge 4p beta Ge Ge βenergyloss Compton plastic scintillator collection point

16. BEDO : BEta Decay studies at Orsay construction completed – commissioning beam time in 2012 4 EXOGAM small prototypes Source-cap distance = 5 cm evaluated eg(1 MeV) = 3-4 % (previous system 1-2%) sensitivity 0.1 pps beam entrance up to 5 Ge detectors 6 plastic detectors Anti-Compton belt

17. • What we have learned ? Selection of results, collectivity and evidence of intruder states in the 78Ni region

18. -decay spectroscopy around the Z=32 “curiosity” surface ionization B. Tastet PhD – def. 13th May 2011 PRC 87, 054307 (2013) laser ionization (10 µA electron primary beam) K. Kolos PhD – def. September 2012 PRC 88, 047301 (2013) D. Testov PhD – def. 17th January 2014 Ga83 Ga82 Ga80 Ga79 Ge80 Ge79 Ge81 Ge85 Ge86 As82 Zn81 Ga84 Ga85 Zn82

19. isomerism in the N=49 line Hoff & Fogelberg NPA368 (1981) (3-5) (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 8+ 6+ 4+ 2+ 0+  existence of second beta decaying state with I~7 suspected ISOLDE experiment, laser spectroscopy : two long lived states in 80Ga I=3and I=6(negative parity from shell model) B. Chealet al., PRC 82(2010) 051302R

20. Study of 80Ga→80Ge beta decay hits per 0.5 keV Energy (keV)

21. Study of 80Ga→80Ge beta decay 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

22. Study of 80Ga→80Ge beta decay apparent half-life of the 80Ge levels T1/2=1.6870.011s Singh Nuclear Data sheets 105 (2005) 223 longer lived ALTO 238U shorter lived Hoff & Fogelberg235U measured half-life in seconds

23. Study of 80Ga→80Ge beta decay levels of 80Ge 80Ga lL longer lF(indirect feeding apparent half life) shorter lS lA(apparent half life) 80Ge shorter lived state contribution 1 0,8 0,6 0,4 0,2 0 longer lived state contribution

24. Study of 80Ga→80Ge beta decay 80Ga T1/2= 1.90.1 s longer shorter T1/2= 1.30.2 s 6― 3―

25. multiplets close to the 0(6) limit of IBM JUN45 JJ4B 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)

26. shell model calculations and transcription into intrinsic shapes JUN45 JJ4B Kumar model-independent n-body moments [Kumar PRL28, 249 (1972)]  intrinsic shapes of SM eigenstates

27. microscopic origin of the collective features non-collective quasi-particle like configurations collective gamma-soft configurations g9/2 p1/2 g9/2 g9/2 p3/2 p1/2 p1/2 f5/2 p3/2 p3/2 n p f5/2 f5/2 n n p Dℓ=2 p pairing components of the interaction quadrupole components of the interaction JJ4B JUN45 ►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

28. Triaxiality at Z=32

29. Triaxiality at Z=32 and possible intruder 2p-2h 0+ states at N=48 evolution of the 0+2 state energy “triaxial features” 76Ge 0+2 ?

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

31. -decay spectroscopy around the Z=32 “curiosity” laser ionization (10 µA electron primary beam) K. Kolos PhD – def. September 2012 PRC 88, 047301 (2013) Ga83 Ga82 Ga80 Ga79 Ge80 Ge79 Ge81 Ge85 Ge86 As82 Zn81 Ga84 Ga85 Zn82

32. Study of84Ga5384Ge52 decay Lebois et al. Kolos et al.

33. Study of84Ga5384Ge52 decay (0—,1—)

34. 84Ga5384Ge52 : addressing the collectivity development beyond N=50 6+ 3095 23+ 2838 02+ 1934 4+ 1744 22+ 1542 2+ 710 0 0+ HFB-5DCH Gogny D1S Delaroche et al. Bruyères-le-Châtel, available online, S. Hilaire M. Girod

35. (1+,2+) 3502 2900 6+ 51+ 2812 43+ 2603 405 229 231 32+ 2360 (0+,1+,2+) 2228 24+ 42+ 6+ 3095 2150 2130 31+ 2002 145 23+ 2838 23+ 1873 77 02+ 1768 166 599 137 4+ 1584 22+ 1530 (1+,2+) 1389 370 269 02+ 1934 4+ 1744 2+ 769 22+ 2+ 624 1542 346 0 0+ 0+ 0 2+ 710 EXP HFB-5DCH Gogny D1S JJ4B(proton-proton)+Sieja et al PRC 79, 064310 (2009) 0 0+ g (°) b =

36. A bit deeper into the problem of intruder states: odd isotones N=49 • What we have learned ? Selection of results collectivity and evidence of intruder states in the 78Ni region

37. A bit deeper into the problem of intruder states: the case of the odd-odd N=49 isotones • odd-odd nuclei: • detailed spectroscopy: stopped beam experiments • -decay very selective as allowed GT transitions e-e→o-o • practically exclusively 0+→1+ PhD A. Etile (CSNSM Orsay) ongoing first data taken with the new -decay spectroscopy setup BEDO (BEDO commissioning) Ge80 Ga83 Ga82 Ga80 Ga79 Ge81 Ge85 Ge86 As82 Ge79 Ga84 Ga85 Zn82 Zn81

38. 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 By Winger et al. PRC 36 (1987) By Kratz et al. PRC 38 (1988) «  »  Waiting point nucleus at N=50 80Zn

39. in a similar study Winger et al removed the parenthesis only at much higher energy Fig. taken from Kratzet al. PRC 38 (1988) Winger et al. PRC 36 (1987) 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 (!)

40. 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 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 ? Hoff& Fogelberg (1981) Winger et al (1987) Eidens et al (1970)

41. Study of 82Ge→82Asbeta decay (Still a bit preliminary) B(%) log ft 0.35(9) <1 5.8(2) (0,1) 1.45(2) 1.6(5) 5.3(2) <1 (0,1) 3.5(5) 100(3) 80(20) 4.2(2) 8.50(6) 5.7(2) 3.4(9) (0-,1-) H. Gausemel et al., Phys. Rev. C 70, 037301 (2004)

42. what are the proton-neutron configurations one can expect at low energy ? → let’s start with the zero-order coupling odd-proton N=50 nucleus (taken from experimental level scheme) odd-odd N=49 nucleus (we hope to describe) O-O O-π proton open shell (proton quasi-particles) O-ν E-E odd-neutron N=49 nucleus (taken from experimental level scheme) even-even semi-magic core neutron closed shell (neutron holes and intruder states)

43. Neutron states Omnipresence of positive parity (intruder) states First 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 states 2+ 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)

44. Proton states A. Pfeiffer et al. NPA 455 (1986) 381

45. Proton states from beta-decay D.V. et al. PRC 76, 054312 (2007) 5/2 assignment to ground state unambiguously confirmed from laser spectroscopy measurements Chealet 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)

46. Unperturbed positions of the proton-neutron configurations in the odd-odd N=49 isotones intruder negative parity normal positive parity 82As is the first N=49 isotone for which low-spin negative parity (0- and 1-) states appear below the first 1+ state

47. 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 : The description of odd N=49 nuclei down to 85Kr, including 2d5/2, 3s1/2, 2d3/2has already been done: Kitching Z. Phys. 258 (1973) ; Bhattacharya & Basu J. Phys. G 5 (1979) Hoffmann-Pinther & Adams [NPA229 (1974)] have already treated the odd-odd case within the Thankappan-True [Phys. Rev. 137 (1965)] schematic approach C - ν Core QP ν C - π QP π π-ν interaction experimental values fit to the odd nuclei strength adjusted on 86Rb

48. experimental coupled to 0+ coupled to 2+ in agreement with identifications made by Dawson et al. Phys. Rev. 181 (1969)

49. experimental coupled to 0+ coupled to 2+ 2+ core coupled states ? B(%) log ft 0.35(9) <1 5.8(2) (0,1) only states coupled to 2+ 1.45(2) 1.6(5) 5.3(2) <1 (0,1) 3.5(5) 100(3) 80(20) 4.2(2) 8.50(6) 5.7(2) 3.4(9) (0-,1-) (clearly) π p3/2νp1/2-1 intruder π f5/2 ν d5/2

50. in a similar study Winger et al removed the parenthesis only at much higher energy Fig. taken from Kratzet al. PRC 38 (1988) Winger et al. PRC 36 (1987) 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 (!)