N. Pietralla TU Darmstadt

1. Study of the effect of shell stabilization of the collective isovector valence-shell excitations along the N=80 isotonic chain N. Pietralla TU Darmstadt J. Leske, L. Coquard, O. Möller, T. Möller, Th. Kröll – TU Darmstadt G. Rainovski, M. Danchev, K. Gladnishki – UNI Sofia J. Jolie, A. Blazhev, D. Mücher, C. Fransen,N. Warr, - UNI Cologne D. Jenkins, R. Wadsworth, C. Barton – UNI York R. Krücken – TU Munich

2. 1 N 1 Wu Physics case – what are the MSSs? Simple Example: Harmonic Oscillator, N=2 IBM-2 A. Arima, F. Iachello

3. ANL program – Coulomb excitations reactions in inverse kinematics with stable beams at GAMMASPHERE g7/2 g7/2-2 The properties of MSSs are sensitive to the sub-shell structure!!! Z=50 h11/2-2 N=80 N=82

4. Theoretical interest I Microscopic description in the framework of the Quasiparticle-phonon model N. Lo Iudice, Ch. Stoyanov, D. Tarpanov PRC 77, (2008) 044310 Consistent description of the MSSs of 134Xe, 136Ba and 138Ce, including the fragmentation in latter one, required slight (300 keV) increase of the energy gap betweeng7/2andd5/2orbitals  “paring correlations weaker than previously thought” The splitting of M1 strength in 138Ce is a genuine shell effect caused by the specific shell structure and the pairing correlations.!

5. Theoretical interest II Original interaction Modified pairing Microscopic description in the framework of the Large Scale Shell Model K. Sieja, G. Martínez-Pinedo, L. Coquard, N. Pietralla (accepted at PRC) Interaction: GCN5082 – realistic Bonn-C potential + empirical correction to the monopole part Space: {0g7/2, 1d5/2,1d3/2, 2s1/2, 0h11/2} for both protons and neutrons – NATHAN and ANTOINE • the SM calculations with modified version of the interaction predict a parabolic behavior in the evolution of B(M1) from 132Te to 138Ce  • MSSs are sensitive to the sub-shell structure • information on MSSs provides a tool to determine the pairing matrix elements of realistic interactions as they depend very sensitively on the treatment of core polarization corrections. • “experimental information on MSSs of 132Te and 140Nd is needed.”

6. 140Nd - status E. Williams et al., AIP Conf. Proc. 1090 (2009) 268. =-0.08(8) 99(1)% M1 =0.186(85) 97(4)% M1 Experiment SM predictions K. Sieja et al. (accepted at PRC) QPM prdictions Ch. Stoyanov (PRC 88 (2008)) GCN5082 - original GCN5082 - modified

7. Experimental approach Coulomb excitations in inverse kinematics on C target predominantly one-step processes and clean -spectrum (no target excitations) 15h at 6.109 pps! 107pps for 2 weeks 1/25 106pps for 2 weeks 1/250 To identify excited 2+ states (beyond the 2+1) in vibrational nucleus (B(E2)~1Wu) with a 10% array for 2 weeks beam time we need 105pps. For complete spectroscopy 106-107 pps will be needed! 1/2500 105pps for 2 weeks Feasible, but requires beam energy 85% CB (498 MeV for 140Nd, 3.5-4 MeV/n) HIE ISOLDE + MINIBALL

8. Experimental Plan • Beam development – beams of 140Nd and 142Sm with sufficiently high primary intensity ( > 107 ions/s) ThOx or Ta targets, LaB/GdB-cavities • RILIS development – ionization scheme for Nd and Sm recently tested. On-line test of Nd and Sm transmission with RILIS is needed! To suppress both stable (140Ce and 142Nd ) and radioactive (140Pm, 140Pr and 142Pr, 142Eu ) isobars • Physics problems – for the Coulomb excitation experiment on C target we need to know the lifetimes of the 2+1 states for precise relative measurement Difficult (impossible) to measure this lifetimes using conventional techniques! Yrast isomers:140Nd -(7-)=0.6(7) ms, (10+)=32.9(13) ns 142Sm -(7-)=240(3) ns, (10+)=679(85) ns Coulomb excitation in inverse kinematics!

9. Measurement of the lifetimes of 2+1 states of 140Nd and 142Sm (this proposal; after development of the 140Nd and 142Sm RILIS beams) • Beams 140Nd and 142Sm – beam energy 2.85 MeV/n ( 400 MeV) • beam intensity n x 105 ions/s on the target (expected) • Target 48Ti – well known B(E2;0+1→2+1), low CB and -rays which do not interfere with ones from the projectile: E2(140Nd) = 773 keV, E2(142Sm) = 768 keV while E2(48Ti) = 983 keV similar cross-sections Other possibilities: 52Cr, 58Ni • Experimental set-up – MINIBALL (7% efficiency for 1.3 MeV) • + CD detector(angle coverage 16-53) In the angular range of 20-53 only scattered Ti ions will be detected! Kinematical Doppler correction!

10. Measurement of the lifetimes of 2+1 states of 140Nd and 142Sm 4. Yields estimation: • B(E2;0+1→2+i) – from the QPM calculations for 140Nd (Ch. Stoyanov, priv. comm.); • CLX code; • Slowing down of the beam in the target was taken into account; • The CE cross-section are calculated for the angular range of interest 20-53; 3 shifts (1 day) running time * QPM predictions

11. Beam time request • 5 shifts for developing and delivering 140Nd beam on the target position at 2.85 MeV/u; • 4 shifts for CE yields measurement of 140Nd beam in combined laser on/off mode; • 5 shifts for developing and delivering 142Sm beam on the target position at 2.85MeV/u; • 4 shifts for CE yields measurement of 142Sm beam in combined laser on/off mode; Total Request: 9 shifts per isotope - in total 18 shifts

12. LoI submitted to INTC in 2007 Decided not to endorse this Letter of Intent! Here it is. Please support it !

13. Thank you ! • 5 shifts for developing and delivering 140Nd beam on the target position at 2.85 MeV/u; • 4 shifts for CE yields measurement of 140Nd beam in combined laser on/off mode; • 5 shifts for developing and delivering 142Sm beam on the target position at 2.85MeV/u; • 4 shifts for CE yields measurement of 142Sm beam in combined laser on/off mode;