Precision mass measurements of n-rich nuclei between N=50 and 82. Short overview on the experimental approach Penning trap mass measurements on n-rich nuclei Impact of improved knowledge of masses – Fine structure of mass surface vs. nuclear structure – two-neutron separation energies – odd-even staggering and pairing Conclusions and outlook Juha Äystö Department of Physics, University of Jyväskylä, Finland Helsinki Institute of Physics, Helsinki, Finland 1

2 RIs (T 1/2 ≈100 ms)

Penning trap Homogenous B, quadrupolar V Three eigenmotions – Axial ( z ) – Magnetron ( - = 1 kHz) – Modified cyclotron ( + =1 MHz) Homogenous B, quadrupolar V Three eigenmotions – Axial ( z ) – Magnetron ( - = 1 kHz) – Modified cyclotron ( + =1 MHz) Split ring electrode: – Dipolar RF – Quadrupolar RF Coupling at c Split ring electrode: – Dipolar RF – Quadrupolar RF Coupling at c SIDEBAND MASS SPECTROMETRY: 3

IGISOL3 fast universal method RFQ + 2 Penning traps Isobaric/-meric cleaning Mass measurements RFQ + 2 Penning traps Isobaric/-meric cleaning Mass measurements T. Eronen et al., Eur. Phys. J. A 48 (2012) 46 -fast, universal 4

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Beam purification Sideband cooling technique (G. Savard et al., Phys. Lett. A 158 (1991) 247) R = M/  M up to

Precision trap – TOF-ICR 7

JYFLTRAP mass measurements 1. N=50 shell closure 2. N≈60 subshell Sn region ~0.1…20 keV precision (10 -9 …10 -7 ) Nuclear structure Nuclear astrophysics (r process) Fundamental symmetries rp, νp process SnSbTe 58 Ni 0 + → 0 + IMME mirror 8

Production in p-fission refs.: V. Rubchenya, J. Äystö, Eur. Phys. J. A 48 (2012) 44 H. Penttilä et al., Eur. Phys. J. A 48 (2012) Rh 9

=(N-Z)/2 Difference between 2003 mass data from the PT data From a review by A. Kankainen, J. Äystö and A. Jokinen, J. Phys. G. submitted

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deformed N=60 region ISOLTRAP TITAN; new JYFLTRAP 12

Charge radii and two-neutron binding energies 13

S 2n versus proton number 14

Neutron-rich masses close to 132 Sn JYFLTRAP ISOLTRAP T 1/2 ≈100 ms J. Hakala, J. Dobaczewski et al., submitted to PRL (2012); arXiv: J. Hakala, J. Dobaczewski et al., submitted to PRL (2012); arXiv: Isomers! (T 1/2 > 100 ms) Agreement with ISOLTRAP data Is PERFECT! 15

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Two-proton shell gap for Z=50Two-neutron shell gap for N= Evolution of shell structure at Z=50 and N=82 Shell gap 17

…theory vs. experiment ? M. Bender, G. F. Bertsch, and P.-H. Heenen. Global study of quadrupole correlation effects. Phys. Rev. C, 73 (2006) S. Goriely, N. Chamel, and J. M. Pearson Skyrme-Hartree-Fock-Bogoliubov nuclear mass formulas: Crossing the 0.6 Mev accuracy threshold with microscopically deduced pairing. Phys. Rev. Lett., 102 (2009) Correlations are very important !! 18

Odd-even staggering (OES); a measure of empirical pairing gap 3-point formula OES mostly depends on the intensity of nucleonic pairing correlations in nuclei but is also affected by the polarisation effects! OES(N odd )  measure of pairing effects OES(N even )  impacted by single particle states around Fermi level 19

d 5/2 g 7/2 20

Odd-even staggering across the N=82 shell closure J. Hakala, J. Dobaczewski et al., arXiv: J. Hakala, J. Dobaczewski et al., arXiv:

Our QRPA calculations reproduce the behavior seen in experiment. We trace the cause to the difference in neutron pairing below and above N=82. Coulomb Excitation of Radioactive 132,134,136Te Beams and the Low BE2 of 136Te PHYSICAL REVIEW LETTERS 88 (2002) D. C. Radford,et al. 22

Conclusion: The N=81-83 asymmetry in staggering indicates - exclusion of pure surface pairing force - significant role for polarization effects for Te and Xe! Dobaczewski, Flocard, Treiner, Nucl. Phys. A 422(1984)103 Spherical self-consistent calculation using Sly4 energy density functional plus contact pairing 23

1  b 1 mb 24

Special issue for IGISOL Science Fall of 2012: IGISOL and JYFLTRAP will MCC30 & K130 cyclotrons Laser hutPenning traps RFQ-buncher 25

Summary Our knowledge of binding energies of neutron-rich nuclei has experienced a major revision during the last five years due to Penning-trap technique Long isotopic chains from Ni to Pr, excluding iodine, measured at three Penning trap facilities: Jyvaskyla, CERN-ISOLDE and Argonne Masses of over 300 nuclides produced in fission with uncertainties of 10 keV or less have become available. The present data set provides : – A challenge for future development of mass models and theories – Higher sensitivity to reveal shape transitions and (sub)shell closures by mass differentials – A new tool to study odd-even staggering of binding energy as a probe for pairing effects in n-rich nuclei (in particular close to drip-line!) Our knowledge of binding energies of neutron-rich nuclei has experienced a major revision during the last five years due to Penning-trap technique Long isotopic chains from Ni to Pr, excluding iodine, measured at three Penning trap facilities: Jyvaskyla, CERN-ISOLDE and Argonne Masses of over 300 nuclides produced in fission with uncertainties of 10 keV or less have become available. The present data set provides : – A challenge for future development of mass models and theories – Higher sensitivity to reveal shape transitions and (sub)shell closures by mass differentials – A new tool to study odd-even staggering of binding energy as a probe for pairing effects in n-rich nuclei (in particular close to drip-line!) 26

Thank you for your attention! …and T. Eronen, A. Kankainen, A. Jokinen and colleagues at 27

masses vs. two different r-process paths P.A. Seeger, W.A. Fowler, and D.D. Clayton. Nucleosynthesis of heavy elements by neutron Capture, Astrophys. J. Suppl. Ser., 11:121, V. Bouquelle, N. Cerf, M. Arnould, T. Tachibana, and S. Goriely. Single and multi-event canonical r-process, Astron. Astrophys., 305:1005, jan

Ion Guide (Light ion induced fusion) Ions. Atoms too, but they’re lost. 29

Continuous RF excitation 200 ms Purification cycles + pulsed RF excitation ms 131 In states g.s: 9/2 +, 280 ms 1/2 -, 302(32) keV, 350 ms 21/2 +, 3764(88) keV, 320 ms (1/2 - ) JYFLTRAP result: E * (1/2 - )=365(8) keV To be published by A. Kankainen et al. 30

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Isomers can be separated (500 ms) 1.7 Hz, 233 keV/c 2 T. Eronen et al., NIM B 266 (2008)

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