Proposal to the ISOLDE and NTo F Committee

Proposal to the ISOLDE and NTo. F Committee High-precision mass measurements below 48 Ca and in the rare-earth region to investigate the proton-neutron interaction P 267

Masses and nuclear structure

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

Double differences ( Vpn values) =average interaction of the last proton and neutron J. -Y. Zhang et al, PLB 89 Cakirli et al. , PRL 05 Unlike p-n orbits large p-n overlap Similar p-n orbits Single-particle structure Small p-n overlap Collectivity/ deformation Shell effect Collectivity grows slower where proton-neutron interaction is small (= Vpn is small) Cakirli, Casten, PRL 06

Masses and (collective) excited levels Structure: deformation/ collectivity IBA calculations for structure and binding energies 0+ 1422 ke. V 0+ 1217 ke. V Which one is the lowest collective excitation? 168 Er 0+ 1422 ke. V collective 0+ 1217 ke. V 168 Er Cakirli et al, PRL 09 in print N

Masses and nuclear structure: recent results from ISOLTRAP

Separation energies Neutron separation energy 80, 81 Zn FRDM: no shell quenching mass of 82 Zn: derived from systematic trends No evidence for shell quenching: N=50 is a good magic number ETFSI-Q: shell quenching S. Baruah et al. , PRL 08 neutron shell gap 132 Sn 132, 134 Sn Restoration of N=82 gap M. Dworschak et al, PRL 08

Vpn Z Vpn trend smoothens n-rich Xe 11 new masses 4 studied 1 st time directly n-rich Cd N n-rich Rn New nuclide identified: 229 Rn Neidherr et al, PRL 09, accepted Unique Vpn behaviour around N=135: Connection to octupole deformation?

Physics interest and the proposed mass measurements

Flattening of S 2 n values around Z=70 and N=108 subshell closure or other structural changes? Deformations: known shapetransition region

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

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

Nuclides with unknown masses but known R 4/2 or E(21+) values Deformation region in neutron-deficient rare earths 68 shapes are expected to change rapidly (MINIBALL proposal, P 257) 66 64 62 Z 65 70 And n-rich 138 Te and 160 Sm 75 80 Help determine the structure N

Experimental setup

ISOLTRAP 2 m determination of cyclotron frequency (R = 107) removal of contaminant ions (R = 105) 10 cm Time of flight [ms] B = 5. 9 T B = 4. 7 T Bunching of the continuous beam

Important setup features Precision: routinely <5 e-8 relative uncertainty (= 7 ke. V for A=150) Present residual systematic limit: 8 e-9*m Half-lives: time spent in the setup: 0. 1 – several s; Shortest t 1/2 at ISOLTRAP: 65 ms (74 Rb) Shortest t 1/2 at a Penning trap mass spectrometer: 11 Li (9 ms) Yields: single-ion resonances with 1 -10% efficiency: measurements with 100 particles/s Discovery potential: The case of 229 Rn Contamination: Resolving power 105 -106 up to 100 -1000 times more of the contaminant than the beam

ISOLDE yields

39 -44 S: requested in another LOI (t 1/2 of 30 S) - Molecular beam (SCO+) with a FEBIAD plasma ion source or negative ions - 2003: 8 e 3 ions/m. C of 38 S (Zr. O 2 target + plasma ionization) 46 -48 Ar: new efficient arc-discharge ion source (VADIS), used by ISOLTRAP in Aug 08 for Xe and Rn isotopes - Expected yields >1 e 4 ions/m. C 138 Te: official Te yields only from SC ISOLDE -COMPLIS (UCx+ hot plasma): 131 -134 Te: >1 e 9 ions/m. C; 135, 136 Te also studied; isobars: Cs, I, Sb with yields lower than Te - A=138 – expected isobar 138 Cs (t 1/2=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 - 150 Ce, 154, 156 Nd, and 158, 160 Sm 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 186 Hf: SC yield for 180 Hf (Ta target) 3 e 6 ions/m. C PSB, NICOLE: 177, 179 -184 Hf (hot plasma Ta/W/Ir target + CF 4), 185 Hf observed

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

d. Vpn values

Vpn in neutron-rich rare-earth nuclides Even-even N 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, PRC 06 Even-odd N

Nuclides with unknown masses but known R 4/2 or E(21+) values

Nuclides with unknown masses but known R 4/2 or E(21+) values

Masses and (collective) excited levels Structure: deformation/ collectivity IBA calculations for structure and binding energies 0+ 1422 ke. V 0+ 1217 ke. V Which one is the lowest collective excitation? 168 Er 0+ 1422 ke. V collective 0+ 1217 ke. V 168 Er Cakirli et al, PRL 09 in print N

Yields

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