150 likes | 259 Views
Study of isomeric states using gamma spectroscopy around N=40.
E N D
Study of isomeric states using gamma spectroscopy around N=40 C. Petrone1,2, J. M. Daugas3, M. Stanoiu1, F. Negoita1, G. Simpson4, C. Borcea1, R. Borcea1, L. Caceres5, S. Calinescu1, R.Chevrier3, L. Gaudefroy3, G. Georgiev6, G. Gey4, C. Plaisir3, F. Rotaru1, O. Sorlin5, J. C. Thomas5 1 HoriaHulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Bucharest- Magurele, Romania 2 Faculty of Physics, University of Bucharest - P.O. Box MG 11, RO 77125, Bucharest-Magurele, Romania, EU 3 CEA, DAM, DIF, F-91297 Arpajon, France 4 ILL, 38042 Grenoble Cedex, France 5 Grand Accélérateur National d’IonsLours (GANIL), CEA/DSM-CNRS/IN2P3, Caen, France 6 CSNSM, CNRS/IN2P3, 91405 Orsay-Campus, France Carpathian Summer School of Physics Sinaia 2012 cristina.petrone@tandem.nipne.ro
67Fe Motivation:Neutron-rich nuclei around N = 40 • Nuclear structure informations far from stability • N = 40 subshell closure for Ni R.Broda et al., Phys.Rev.Lett. 74 (1995) • Deformation in 66Fe vanishing • Isomeric state in 67Fe M.Sawicka et al., Phys.Rev.C 77,054306(2008) • Nuclear structure of neutron-rich nuclei lying • between 68Ni and 78Ni-> modelization of • astrophysical processes
50 g9/2 40 f5/2 p3/2 28 f7/2 p n J.-M. Daugas Phys.Rev.C 81 (2010) 86Kr on Ni target 2 isomeric states The key role of the n g9/2 for 40 < N < 50 • Neutron-rich Cu isotopes (Z=29): • 1 p outside Z=28 core interacting with ng9/2 • Spin-isospin interaction • Tensor force 75Cu • N = 46 (75Cu):p1f5/2 g.s. configuration • K.Flanagan , Phys. Rev.C80(2009) 1096 1|2- 454 1|2- 1|2- 1|2- 135
LEPS Fragments 70° HPGe Veto (Si) Electron detector (SILI) HI-detectors(Si) Shield Experimental set-up • Fragmentation of 86Kr @ 60 MeV/u on Be (500um) • Beam intensity: 4 mAe Veto detector: Double Side Strip Si detector Fragments separated in flight using LISE2000 Compact reaction chamber -> high efficiency detection Implantation foil (Kapton) 75 um Effective thickness = 219 um Al degrador A, Z identification by Energy-loss and TOF informations Si position sensitive detectors
Identification matrix • ΔE, ToF, Bρ • Delayed γ-ray correlations 78Ga31+ Z 75Cu29+ +72Cu28+ AoQ
75Cu gamma spectrum J.M.Daugas et al., Phys.Rev.C 81(2010) 62.2(4)keV 66.5(4)keV 66.5keV transition 62.2keV transition E(keV) T(ns)
γ-γ coincidences Coincidence spectra 66.5keV gated Coincidence spectra 62.2keV gated E(keV) E(keV) 51 270(1.76us) 6- Coincidence spectra background gated 82 220 4- 138 3- 138 2- 72Cu decay scheme M.Stanoiu PhD thesis (2003) E(keV)
Gamma times • Fit function: convolution between a gaussian and an exponential T1/2=149(6)ns 66.5keV gated T1/2=296(10)ns 62.2keV gated T(ns) Almost 100%feeding from the uppper isomeric state T(ns)
75Cu- possible decay schemes Systematics of the energies of the 1/2- 5/2- states in 63-73Cu Estimation for internal conversion coefficients T. Kidebi et al., Nucl.Instrum. Methods A 589(2008) M1 E2 M1 M1 3/2- 1/2- 66.5 66.5 E2 M1 3/2- 1/2- 62.2 62.2 Scenario A Shell model calculation : B(E2)=19.9 W.u. for 62.2keV transition B(M1)=0.009 W.u for 62.2keV transition Scenario B 5/2- 5/2- • B(E2; 1/2– 5/2–)=22.9(4) W.u. • B(M1; 3/2– 5/2–)=2.2(5)*10-4 W.u. • B(E2; 1/2– 5/2–)=7.89(5) W.u. • B(M1; 3/2– 5/2–)=1.51(4)*10-4W.u.
78Ga : gamma spectrum 2- J.-M. Daugas PhD thesis (1999) E. Mane et al., Phys. Rev. C 84(2011) 218.4(2) 281.3(2) 157.5(2) 60.2(2) 211(5) 341.3(3) 498.9(8) E(keV)
78Ga:time spectra Coincidence spectra gated on 281.4keV transition -> 211+2281.4=492.4(3)keV energy of the decaying state T1/2=111(2)ns 280keV gate 211keV new transition T(ns) E(keV) T1/2=110(5)ns 211keV gate • Background subtraction • Fit function: convolution between a Gaussian and an exponential function • Same half-life • Feeding from the isomeric state-> 6.6(3)keV transition between the two state T(ns)
78Ga: transition probabilities 499keV transition (1.33*10-5 s) • B(E1)= 1.35(7)*10-9W.u • B(E2)= 2.88(2)*10-4W.u • B(E3)= 1.36(5)*10-2W.u • B(M1)= 5.52(3)*10-8W.u • B(M2)= 1.33(7)*10-1W.u • B(M3)= 8.08(4)*103W.u • 157.4keV transition (9.78*10-7 s) • B(E1)= 1.27(3)*10-7W.u • B(E2)= 3.96(1)*10-1W.u • B(E3)= 1.87(5)*106W.u • B(M1)= 7.55(2)*10-6W.u • B(M2)= 1.82(5)*102W.u • B(M3)= 1.11(4)*108W.u 218keV transition (2.03*10-7 s) • B(E1)= 3.58(7)*10-7W.u • B(E2)= 4.02(2)*10-1W.u • B(E3)= 9.95(5)*105W.u • B(M1)= 1.47(3)*10-5W.u • B(M2)= 1.85(4)*102W.u • B(M3)= 5.92(4)*107W.u 6.6keV (211keV) transition (3.99*10-6 s) • B(E1)= 4.55(3)*10-7W.u • B(E2)= 3.58(2)*10-2W.u • B(E3)= 9.46(2)*104W.u • B(M1)= 1.23(2)*10-6W.u • B(M2)= 1.65(3)*10W.u • B(M3)= 5.63(8)*106W.u
New spin and parity assignments • Jj44b ->better match with the data overall • Predicts the gradual drop in 2- energy from 74Ga to 78Ga • Same proton configuration as 72,74Cu E2 E2 E2 M2 1+ 498.9 M2 2+ 492.3 4- 341.3 4- 281.3 g.s 2- P.C. Srivastava ,J.Phys.G39(2012) Proposed level scheme for 78Ga
Summary 75Cu • New parity and spin assignments • New level scheme based on γ-γ coincidences results 78Ga • New observed level :492.3(3) keV • New parity and spin assignments • Partial agreement with theoretical models
Thank you Acknowledgments • We are grateful for the technical support provided to us by staff at the GANIL facility. • The author C.Petrone is grateful for the financial support from the European Social Fond through POSDRU 107/1.5/S/80765 Project.