First lifetime measurements in the 78 Ni region with AGATA and VAMOS at GANIL

Transcription

1 First lifetime measurements in the 78 Ni region with AGATA and VAMOS at GANIL Clément Delafosse Institut de Physique Nucléaire d Orsay for the E669 collaboration Colloque GANIL Amboise

2 Physics motivation : the Z=32 «triaxiality corridor»? γ 3 + γ γ γ 3 + γ 2 + γ γ-soft Wilets & Jean γ-rigid Davydov & Filippov

3 Physics motivation : the Z=32 «triaxiality corridor»? 76 Ge44 (stable) proven to be triaxial S. Mukhopadhay et al. PRC 95, (2017) (n,n γ) Y. Toh et al. PRC 87, (R) (2013) (multistep-coulex) Detailed knowledge of the E2 strength distribution HFB-GCM Gogny D1S (Delaroche et al. Bruyères-le-Châtel, available online

4 Physics motivation : the Z=32 «triaxiality corridor»? 76 Ge44 (stable) proven to be triaxial S. Mukhopadhay et al. PRC 95, (2017) (n,n γ) Y. Toh et al. PRC 87, (R) (2013) (multistep-coulex) Hints of triaxiality in exotic 80,84,86,88 Ge 84 Ge (M. Lebois et al. PRC 80, (2009)) (ALTO) E(4 + )/E(2 + ) ratio + GCM 80 Ge (D. Verney et al. PRC 87, (2013)) (ALTO) Level scheme and spin assignment (2 +, (3 + ),4 + states) + shell model 84,86,88 Ge (M. Lettman et al. PRC 96, (R) (2017)) (RIKEN) E(4 + )/E(2 + ) ratio + shell model

5 Physics motivation : the Z=32 «triaxiality corridor»? B(E2; ) values are well reproduced in 74,76,78 Ge42,44,46 HFB-GCM Gogny D1S (Delaroche et al. Bruyèresle-Châtel, available online)

6 Physics motivation : the Z=32 «triaxiality corridor»? B(E2; ) values are well reproduced in 74,76,78 Ge42,44,46 But it not the case in 72,80 Ge40,48 HFB-GCM Gogny D1S (Delaroche et al. Bruyèresle-Châtel, available online

7 Physics motivation : the Z=32 «triaxiality corridor»? B(E2; ) values are well reproduced in 74,76,78 Ge42,44,46 But it not the case in 72,80 Ge40,48 Low lying 0 + state in these two Ge isotopes We may miss something in our models. David C. Camp NPA 121, (1968) A. Gottardo et al. PRL 116, (2016) (ALTO) See D. Verney s presentation

8 Experiment E669 at GANIL VAMOS Magnetic spectrometer VAMOS : Bρ0 = 1.1 T.m at 28 AGATA : 8 triple clusters (24 crystals) Beam : 238U (25 na, 6.3 AMeV) Target : 9Be (2.07 mg/cm2) Degrader : natmg (5 mg/cm2) Target to degrader distances : 120,270 and 520 μm AGATA Advanced γ-tracking array Be target Mg degrader OUPS γ-hits in AGATA Orsay Universal Plunger System NIM A (2012)

9 RDDS : plunger device RDDS : Recoil Distance Doppler Shift If a photon is emitted before or after the degrader, the Doppler shift is different because the velocity is different D = 120(10), 270(10), 520(10) μm The distance D is retro-controlled by computer The correspondance between D and ToF (Time of flight) is given by ToF = D/V (where V is the velocity of the ion before the degrader) The velocity before the degrader is deduced from the velocity measured in VAMOS through the LISE++ software

10 RDDS : plunger device RDDS : Recoil Distance Doppler Shift If a photon is emitted before or after the degrader, the Doppler shift is different because the velocity is different D = 120(10), 270(10), 520(10) μm The distance D is retro-controlled by computer The correspondance between D and ToF (Time of flight) is given by ToF = D/V (where V is the velocity of the ion before the degrader) The velocity before the degrader is deduced from the velocity measured in VAMOS through the LISE++ software R=IU/(IU+IS) evolution as a function of ToF is given by Bateman equation

11 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) Time of flight (ps)

12 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) Time of flight (ps)

13 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) Time of flight (ps)

14 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) Time of flight (ps)

15 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) Time of flight (ps)

16 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) Time of flight (ps)

17 Side feeding side feeding (λsf) λ2 Side feeding : Unobserved transitions modelled as a virtual state with an effective lifetime R=IU/(IU+IS) 120μm 270μm 520μm Time of flight (ps)

18 Fission products identification with VAMOS Target X TMW1: 38 ch Y TMW1: 60 ch T start X TMW2: 64 ch Y TMW2: 92 ch Target MW Proton number X TMW1 Y TMW1 X TMW2 Y TMW2 X,Y DC1 X,Y DC2 X,Y DC3 X,Y DC4 Dipole Target Position X f, Y f, f, f x=500 x=-500 T start T stop z B ρ, D TOF E E MW 0-19 DC 1,2,3,4 IC V B ρ T stop Z M M/Q Q X,Y DC1 X,Y DC2 X,Y DC3 X,Y DC4 20 pads 4x160 pads 4x5 pads Courtesy to J. Dudouet de E Mass

19 Counts Number of ions identified with VAMOS as a function of the number of proton and neutron

20 Counts Number of ions identified with VAMOS as a function of the number of proton and neutron

21 Mass spectra as a function of Z FWHM = 0.6% at A = 86

22 Mass spectra as a function of Z FWHM = 0.6% at A = 86

23 88 Kr Sum of all distances γ-spectrum (+) % 25% (5,6) (5) % 15% Nb coups / 2keV ) (5) + ( % % (5) (5) + + (6 ) Kr 100% Energie [kev]

24 Life time measurement : 88 Kr 2 + -> > 2 + Nb coups / kev Nb coups / kev μm Energie [kev] Energie [kev] Nb coups / kev Nb coups / kev μm (+) <8.4 ps <4.2 ps (5,6) (5) <2.1 ps > ps Nb coups / kev Energie [kev] Nb coups / kev Energie [kev] μm 4 + >11.8 > ps ps R Energie [kev] Energie [kev] 2 + -> > 2 + (a) R (b) Kr ps

25 Life time measurement : 88 Kr 2 + -> > 2 + Nb coups / kev Nb coups / kev μm Energie [kev] Energie [kev] Nb coups / kev Nb coups / kev μm NEW (+) <8.4 ps NEW <4.2 ps (5,6) (5) NEW <2.1 ps NEW > ps R Nb coups / kev Energie [kev] Energie [kev] Nb coups / kev Energie [kev] Energie [kev] 2 + -> > 2 + (a) R (b) 520 μm > Kr > NEW 0.15 NEW 4.3 ps ps NEW 10.6 ps B(E2) (e 2 fm 4 ) B(M1) (μn 2 )

26 86 Se Sum of all distances γ-spectrum 800 (6 + ) 700 Sm Sm Sm Sm % (4 +,5 + ) % 11% Counts / kev ) ( ) ( % Se Energy [kev]

27 Life time measurement : 86 Se 2 + -> > > μm 4 + -> μm (6 + ) <1.5ps 520 μm 4 + > (4 +,5 + ) <2.4 ps > ps ps Se

28 Life time measurement : 86 Se 2 + -> > > μm 4 + -> μm 520 μm (6 + ) 4 + <1.5ps > NEW (4 +,5 + ) NEW <3.6 ps > ps ps Consistant with J. Litzinger PRC 92, (2015) AGATA campaign at LNL B(E2) (e 2 fm 4 ) B(M1) (μn 2 ) Se 345.7

29 84 Ge Sum of all distances γ-spectrum % 100% Ge

30 Life time measurement : 84 Ge Techinics used by J. Litzinger in PRC 92, (2015) counts / kev counts / kev FIT 84Ge Energy [kev] Energy [kev] R (a) level lifetime (ps) R (b) level lifetime (ps) Ge > <10.3 ps 13.8 ps

31 Life time measurement : 84 Ge Techinics used by J. Litzinger in PRC 92, (2015) counts / kev counts / kev FIT 84Ge Energy [kev] Energy [kev] R (a) level lifetime (ps) R (b) level lifetime (ps) Ge > > NEW <13.3 ps NEW <20.7 ps B(E2) (e 2 fm 4 ) B(M1) (μn 2 )

32 Interpretation J. Litzinger et al. PRC 92, (2015)

33 Interpretation Sudden rise of collectivity after the N=50 shell closure Collectivity still rises from Se to Ge at N=52

34 Interpretation Sudden rise of collectivity after the N=50 shell closure Collectivity still rises from Se to Ge at N=52 in contradiction with shell model calculation (Z=34 supposed to be the maximum of collectivity : proton mid-shell) Shell model : K. Sieja, private communication based on theory developed in PRC 88, (2013) and references therein

35 Interpretation Sudden rise of collectivity after the N=50 shell closure Collectivity still rises from Se to Ge at N=52 in contradiction with shell model calculation (Z=34 supposed to be the maximum of collectivity : proton mid-shell) Shell model : K. Sieja, private communication based on theory developed in PRC 88, (2013) and references therein HFB-GCM calculations quite well reproduce this value : coalescence of the 2 coexisting shapes before N=50? HFB-5DCH Gogny D1S (Delaroche et al. Bruyères-le-Châtel, available online

36 Interpretation Sudden rise of collectivity after the N=50 shell closure Collectivity still rises from Se to Ge at N=52 in contradiction with shell model calculation (Z=34 supposed to be the maximum of collectivity : proton mid-shell) Shell model : K. Sieja, private communication based on theory developed in PRC 88, (2013) and references therein HFB-5DCH Gogny D1S (Delaroche et al. Bruyères-le-Châtel, available online HFB-GCM calculations quite well reproduce this value : coalescence of the 2 coexisting shapes before N=50? RHB-DD-PC1: P. Marevic, private communication based on theory developed in PRC 89, (2014)

37 Interpretation 84 Ge52 HFB-5DCH Gogny D1S (Delaroche et al. Bruyères-le-Châtel, available online Shell model : K. Sieja, private communication based on theory developed in PRC 88, (2013) and references therein RHB-DD-PC1: P. Marevic, private communication based on theory developed in PRC 89, (2014)

38 Conclusions First lifetime of excited states measured in 88 Kr Lifetime measured with better accuracy in 86 Se First lifetime measured in the very exotic 84 Ge Unexpected enhancement of collectivity in 84 Ge (due to the N=50 gap weakening at Z=32?)

39 Conclusions First lifetime of excited states measured in 88 Kr Lifetime measured with better accuracy in 86 Se First lifetime measured in the very exotic 84 Ge Unexpected enhancement of collectivity in 84 Ge (due to the N=50 gap weakening at Z=32?) Many results in the 78 Ni region are coming : - Neutron monopole drift towards 78Ni - Intruder states in N=49 isotones Stay tuned!

40 Perspectives - Multistep coulex in Ge isotopes (LoI at SPES, M. Zielinska, D. Verney et al) : E2 strength distribution

41 Perspectives - Multistep coulex in Ge isotopes (LoI at SPES, M. Zielinska, D. Verney et al) : E2 strength distribution - <δr 2 > measurement by laser spectroscopy in N=52 isotones (LINO at ALTO)

42 Perspectives - Multistep coulex in Ge isotopes (LoI at SPES, M. Zielinska, D. Verney et al) : E2 strength distribution - <δr 2 > measurement by laser spectroscopy in N=52 isotones (LINO at ALTO) - Electron conversion spectroscopy : low-lying 0 + state in 84 Ge? (ALTO or/and GRIFFIN/TRIUMF)

43 Thank you for your attention!