High-precision mass measurements below 48 Ca and in the rare-earth region to investigate

1. Proposal to the ISOLDE and NToF Committee P267 High-precision mass measurements below 48Ca and in the rare-earth region to investigate the proton-neutron interaction

2. Masses and nuclear structure

3. One- or two- neutron and proton separation energies Deformation Shell closures

4. large p-n overlap Small p-n overlap Double differences (dVpn values) =average interaction of the last proton and neutron J.-Y. Zhang et al, PLB89 Cakirli et al., PRL05 Unlike p-n orbits Similar p-n orbits Single-particle structure Shell effect Collectivity grows slower where proton-neutron interaction is small (=dVpn is small) Collectivity/ deformation Cakirli, Casten, PRL06

5. collective 0+ 1422 keV 0+ 1422 keV 0+ 1217 keV 0+ 1217 keV Which one is the lowest collective excitation? 168Er 168Er N Masses and (collective) excited levels Structure: deformation/ collectivity IBA calculations for structure and binding energies Cakirli et al, PRL09 in print

6. Masses and nuclear structure:recent results from ISOLTRAP

7. Neutron separation energy 80,81Zn mass of 82Zn: derived from systematic trends 132Sn S. Baruah et al., PRL08 neutron shell gap No evidence for shell quenching: N=50 is a good magic number FRDM: no shell quenching ETFSI-Q: shell quenching 132,134Sn Restoration of N=82 gap M. Dworschak et al, PRL08 Separation energies

8. Z n-rich Xe dVpn trend smoothens 11 new masses 4 studied 1st time directly n-rich Cd N n-rich Rn New nuclide identified: 229Rn Neidherr et al, PRL09, accepted Unique dVpn behaviour around N=135: Connection to octupole deformation? dVpn

9. Physics interest and the proposed mass measurements

10. subshell closure or other structural changes? Deformations: known shape- transition region Flattening of S2n values around Z=70 and N=108

11. Even-even Even- odd p3/2, f5/2 f7/2 dVpn (keV) 26 24 22 20 18 1 400-500 500-600 600-700 700-800 800-900 900-1000 >1000 3 4 5 5 3 f7/2 2 4 2 5 2 4 6 3 1 3 4 5 5 5 5 6 6 d3/2 7 5 5 7 7 Z/N 22 24 26 28 30 32 34 unique feature of shell structure: no sudden change from low-j to high-j orbits when crossing magic N=28 => no sudden dVpn drop expected Possible sub-shell effect Nature of Vpn in light nuclei Vpn values in the 48Ca region South-east of 28Ca: Peak in dVpn followed by a sudden drop

12. Even-even Even-odd N N Vpn in neutron-rich rare-earth nuclides Much larger than for neighbours, also followed by a drop? A systematic peak followed by a drop for N=Z+34 Z 158Sm: surprisingly low value at the diagonal Even-even Exceptionally high values away from the diagonal N Required mass uncertainty <10keV

13. 68 66 64 62 Z N 65 70 75 80 Nuclides with unknown masses but known R4/2 or E(21+) values Deformation region in neutron-deficient rare earths shapes are expected to change rapidly (MINIBALL proposal, P257) And n-rich 138Te and 160Sm Help determine the structure

14. Experimental setup

15. Time of flight [ms] 2 m 10 cm removal of contaminant ions (R = 105) Bunching of the continuous beam ISOLTRAP determination of cyclotron frequency (R = 107) B = 5.9 T B = 4.7 T

16. Important setup features Precision: routinely <5e-8 relative uncertainty (= 7 keV for A=150) Present residual systematic limit: 8e-9*m Half-lives: time spent in the setup: 0.1 – several s; Shortest t1/2 at ISOLTRAP: 65 ms (74Rb) Shortest t1/2 at a Penning trap mass spectrometer: 11Li (9ms) Yields: single-ion resonances with 1-10% efficiency: measurements with 100 particles/s Discovery potential: The case of 229Rn Contamination: Resolving power 105-106 up to 100-1000 times more of the contaminant than the beam

17. ISOLDE yields

18. 39-44S: requested in another LOI (t1/2 of 30S) - Molecular beam (SCO+) with a FEBIAD plasma ion source or negative ions - 2003: 8e3 ions/mC of 38S (ZrO2 target + plasma ionization) 46-48Ar: new efficient arc-discharge ion source (VADIS), used by ISOLTRAP in Aug08 for Xe and Rn isotopes - Expected yields >1e4 ions/mC 138Te: officialTe yields only from SC ISOLDE -COMPLIS (UCx+ hot plasma): 131-134Te: >1e9 ions/mC; 135,136Te also studied; isobars: Cs, I, Sb with yields lower than Te - A=138 – expected isobar 138Cs (t1/2=33 min), required resolving power 7500 • Rare earths: Ce, Nd, Sm, Gd, Dy, Er, Yb • Available at ISOLDE: surface ionization, a lot of contaminants • Improvement in efficiency and purity: laser ionization and low work-function cavities • 150Ce, 154,156Nd, and 158,160Sm requested by us in 2007: development list • RILIS schemes known for Nd, Sm, Gd, Dy, and Yb • Nd: the ionization scheme tested in 2008, Sm: to be tested in spring 2009 • Cavity test planned for 2009 186Hf: SC yield for 180Hf (Ta target) 3e6 ions/mC PSB, NICOLE: 177,179-184Hf (hot plasma Ta/W/Ir target + CF4), 185Hf observed

19. Beam-time request Studies to be performed over 2-3 years

20. dVpn values

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24. Even-even Even-odd N N Vpn in neutron-rich rare-earth nuclides Microscopic interpretation of the peaks: n in the specific Nilsson orbits have increasingly higher overlaps with mid-shell p orbits as N grows from 92 to mid shell Reasonable agreement Oktem et al, PRC06

25. Nuclides with unknown masses but known R4/2 or E(21+) values

26. Nuclides with unknown masses but known R4/2 or E(21+) values

27. collective 0+ 1422 keV 0+ 1422 keV 0+ 1217 keV 0+ 1217 keV Which one is the lowest collective excitation? 168Er 168Er Masses and (collective) excited levels Structure: deformation/ collectivity IBA calculations for structure and binding energies Cakirli et al, PRL09 in print N

28. Yields

29. A new isotope of radon discovered: 229Rn 7 new masses with s<20keV, All never measured directly before 223-229Rn • Nuclear structure: • residual proton-neutron interaction (dVpn values) • possible octupole deformation Neidherr et al., submitted to PRL