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

Masses and nuclear structure

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

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

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

Masses and nuclear structure: recent results from ISOLTRAP

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

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

Physics interest and the proposed mass measurements

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

 Vpn values in the 48 Ca region 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 Even-evenEven- odd South-east of 28Ca: Peak in  Vpn followed by a sudden drop Z/N >1000  Vpn (keV) f7/2 p3/2, f5/2 f7/2 d3/2 1 2

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

Nuclides with unknown masses but known R4/2 or E(2 1 +) values Deformation region in neutron-deficient rare earths And n-rich 138Te and 160Sm N Z shapes are expected to change rapidly (MINIBALL proposal, P257) Help determine the structure

Experimental setup

ISOLTRAP B = 4.7 T B = 5.9 T 2 m determination of cyclotron frequency (R = 10 7 ) removal of contaminant ions (R = 10 5 ) Bunching of the continuous beam 10 cm Time of flight [  s]

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 up to times more of the contaminant than the beam

ISOLDE yields

39-44S: requested in another LOI (t1/2 of 30S) - Molecular beam (SCO+) with a FEBIAD plasma ion source or negative ions : 8e3 ions/  C 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/  C 138Te: official Te yields only from SC ISOLDE -COMPLIS (UCx+ hot plasma): Te: >1e9 ions/  C; 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 Cavity test planned for Hf: SC yield for 180Hf (Ta target) 3e6 ions/  C PSB, NICOLE: 177, Hf (hot plasma Ta/W/Ir target + CF4), 185Hf observed

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

dVpn values

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 Vpn in neutron-rich rare-earth nuclides N N Even-evenEven-odd 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 Oktem et al, PRC06 Reasonable agreement

Nuclides with unknown masses but known R4/2 or E(2 1 +) values

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

Yields

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