R.Burcu Cakirli*, L. Amon, G. Audi, D. Beck, K. Blaum, Ch. Böhm, Ch. Borgmann, M. Breitenfeldt, R.F. Casten, S. George, F. Herfurth, A. Herlert, M. Kowalska, S. Kreim, Y. Litvinov, D. Lunney, S. Naimi, D. Neidherr, M. Rosenbusch, S.Schwarz, L. Schweikhard, R. Wolf, *Max-Planck Institute for Nuclear Physics Heidelberg, Istanbul University CSNSM-IN2P3-CNRS-Orsay, GSI, University of Leuven, WNSL, NSCL, CERN, Johannes Gutenberg-Universität, EMA University High-Precision Mass Measurements in the Rare-Earth Region to Investigate the Proton-Neutron Interaction OUTLINE Motivation and ISOLTRAP Proposed Mass Measurements Beam Time Request

MOTIVATION – S 2n Masses – Nuclear Structure, Nucleon Interactions Separation Energies – Shell Structure, Shape Transitions

MOTIVATION – Valence proton-neutron interactions – critical for evolutions of structure:  V pn *  We can measure!!! Double differences of masses, e.g.  Vpn – average proton- neutron interactions (importance: primarily determine the evolution of structure) Brief introduction Measurement of p-n Interaction Strengths Average p-n interaction between 2 last protons and 2 last neutrons For even-even nuclei:  V pn (Z,N) = - ¼ [ {B(Z,N) - B(Z, N-2)} -{B(Z-2, N) - B(Z-2, N-2)} ]* ( B(Z,N) = [(Nm n + Zm p – m (Z,N) ] c 2 ) * J-y. Zhang and Garrett, 1988

 Vpn (Z,N) = - ¼ [ {B(Z,N) - B(Z, N-2)} - {B(Z-2, N) - B(Z-2, N-2)} ] p n p n Interaction of last two n with Z protons, N-2 neutrons and with each other Interaction of last two n with Z-2 protons, N-2 neutrons and with each other Empirical average interaction of last two neutrons with last two protons  V pn (keV) * * with the first mass measurement of 208 Hg L. Chen et al., Phys. Rev. Lett. 102, (2009)

ISOLTRAP 60 keV ION BEAM B= 4.7T B= 5.9T Determination of Cyclotron frequency, R=10 7 Removal of contaminant ions R=10 5 Depending on A, absolute accuracy of ISOLTRAP is about 10 keV and even less – good enough for both S 2n and  V pn

Two neutron separation energies, S 2n Possible sub-shell closure N~108* (different slope on S 2n ) Yb has a different slope – larger S 2n value at N=108 The region is not a spherical- deformed region (as occurs in the N=90 nuclei nuclei) -- interesting to understand better, in particular Yb 178 Yb 108, 180 Yb 110, 182 Yb 112, 170 Dy 104, 174 Er 106 * M.H.Mortensen et al., PRC 21, 2275 (1980), A. Ansari PRC 33, 321 (1986) R.F. Casten, Nucl. Phys. A443, 1 (1980) M.A.J. Mariscotti et al., Phys. Rev. 178, 1864 (1969) R.B. Cakirli, R.F. Casten, Phys. Rev. C 78, (2008) (R)

Both regions ( A~140 and ~220) -- octupole correlations *** The  V pn values show the same striking, and unique, results --- a kind of parabolic trend in the same region where octupole correlations are known. The validity of this signature needs to be confirmed, and evidence for such correlations needs to be confirmed by spectroscopic data.  V pn values may give first evidence for octupole correlations in new mass regions. OR, shell effect? *D. Neidherr et al., PRL 102, (2009), **PR C80, (2009) *** P.A. Butler, and W. Nazarewicz, Rev. Mod. Phys. 68, 349 (1996). Neutron Number Recent ISOLTRAP results : Rn and Xe masses   V pn Rn : First mass measurements (Discovery of 229 Rn) * Xe mass measurements (First masses for Xe ) **

Large  V pn values expected along the diagonal lines *  V pn ( 158 Sm) B( 158 Sm), B( 156 Sm), B( 156 Nd), B( 154 Nd) Protons and neutrons are filling similar orbits similar FRACTIONAL FILLING f p ~ f n (f p = N p /32, f n = N n / 44) Large p-n interaction R. B. Cakirli, D. S. Brenner, R. F. Casten, and E. A. Millman, Phys. Rev. Lett. 94, (2005) * D. Neidherr, R. B. Cakirli, G. Audi, D. Beck, K. Blaum et al.,Phys. Rev. C 80, (2009)

To test valence proton - neutron correlations in Density Functional Theory (DFT) calculations Experiment Theory (DFT) D. Neidherr et al.,Phys. Rev. C 80, (2009) Additional to  V pn ( 158 Sm) along the diagonal line Er 104, 176 Yb 106, 182 Hf 110, 188 W 114 Needed masses : 170 Dy 104, 174 Er 106, 180 Yb 110, 186 Hf 114 M. Stoitsov, R. B. Cakirli, R. F. Casten, W. Nazarewicz, and W. Satuła,Phys. Rev. Lett. 98, (2007)

Proposed Mass Measurements Precision ~50 keV for S 2n, ~ 10 keV for  V pn S 2n Nuclides of Interest Nuclei to StudyT 1/2 Mass Uncert. (keV) #  exptrapolated 170 Dy 170 Dy (not identified yet) 200 # 174 Er 3.2 min.300 # 178 Yb 74 min Yb 2.4 min.400 # 182 Yb 182 Yb (not identified yet) 400 # 186 Hf 2.6 min.300 #  V pn 158 Sm 154 Nd 156 Nd 158 Sm 25.9 sec sec min Er 170 Dy (not identified yet) 200 # 176 Yb 174 Er3.2 min.300 # 182 Hf 180 Yb2.4 min.400 # 188 W 186 Hf2.6 min.300 #

Beam Time Request AElementShiftTargetIon Source Beams available at ISOLDE: 7 shifts requested (estimated numbers) 186Hf3Ir + CF 4 Hot plasma Nd4UC x + low work-function cavity RILIS Rare-earth beams with possible contamination which can be separated with ISOLTRAP purification trap: 8 shifts (estimated numbers) 168, 170Dy3TaW(surface) 174Er2TaW(surface) 178, 180Yb3Ta/W mixtureW(surface) Rare-earth beams requiring target and ions sources tests SmUC x + low work-function cavity RILIS (to be tested during 2010)

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