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Mass Measurements and Nuclear Structure

Mass Measurements and Nuclear Structure. G. Bollen National Superconducting Cyclotron Laboratory NSCL Michigan State University. Overview and Motivation Mass Measurements at ISOLDE … … and elsewhere Conclusions. Rare Isotope Physics - an expedition by far not completed!.

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Mass Measurements and Nuclear Structure

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  1. Mass Measurements and Nuclear Structure G. BollenNational Superconducting Cyclotron Laboratory NSCLMichigan State University Overview and Motivation Mass Measurements at ISOLDE … … and elsewhere Conclusions

  2. Rare Isotope Physics - an expedition by far not completed! HeaviestElements? Limit of proton-rich nuclei? Known Nuclei Possible Nuclei Limit of neutron-rich nuclei? Binding energies determine limits of existence

  3. How do mass measurements contribute? Isospin Symmetry Pairing Exotic decays Fundamental Interactions Stability of SHE rp-process r-process Magic Numbers Evolution of Shell Structure Halos and Skins

  4. Constraints for nuclear models

  5. Nuclear Structure and Masses Cs Fe 50 56 total binding energies two-neutron separation energies Systematic study of masses – first indicator of new nuclear structure effects

  6. Tools for mass measurements on rare isotopes • Conventional mass spectrometry • CERN-PS + ISOLDE • Chalk-River • St. Petersburg Out of Stock • Time-of-flight spectrometry • single turn: SPEG, TOFI • multi turn: cyclotrons CSS2, SARA, storage ring ESR • Frequency measurements • storage ring ESR/GSI, future NESR, RIBF rings • RF transmission spectrometer MISTRAL/ISOLDE • Penning traps ISOLTRAP/ISOLDE, LEBIT/NSCL, • JYFLTRAP/JYFL, CPT/ANL • SHIPTRAP/GSI, TITAN/TRIUMF, MAFFTRAP/Munich wc = q/m B • + Q-values from reactions anddecays

  7. Comparison of Methods Time-of-Flight TOF Isochronous RF-Spectrometer TOF Schottky Penning Trap  LEBIT  half life (seconds) D. Lunney et al., Rev. Mod. Phys. 75, 1021 (2003).

  8. Mass measurements far from stability at CERN • CERN pioneered direct mass measurements far from stability • Na isotopes (SPS)  discovery of island of inversion • 11Li (SPS)  first loosely bound exotic nucleus discovered • Rb isotopes (ISOLDE)  first subshell closure observed in long isotopic chains • ISOLDE pioneered new techniques for short-lived isotopes • Penning trap mass spectrometry + many related techniques (ISOLTRAP) • RF mass spectrometry (MISTRAL)

  9. RF f = (n + ½) fc magnet fc fc transmitted ion signal (counts) 1 m 505000 505100 505200 frequency (kHz) slit 0.4 mm ion counter ISOLDE 60 kV beam RF B MISTRAL:Mass measurements at ISOLDE with a Transmission RAdiofrequency spectrometer on-Line Resolving Power R= 100000 Sensitivity: 500/s FAST: very shortT1/2 reference beam D. Lunney/Orsay

  10. Mass measurements of halo nuclei - 11Li MIS RAL C. Bachelet, Ph.D. thesis (2004), EPJ A direct DOI: 10.1140/epjad/i2005-06-005-5 MISTRAL: S2n=376(5) keV20% higher than currently used to adjust models... Graphics: I. Tanihata

  11. 11Be, 12Be, towards 14Be MIS RAL Test run (Sept. 2005) : new mass for 12Be (T1/2 = 21 ms) New Paul-trap Beam cooler

  12. How magic are magic numbers? SPEG/GANIL H. Savajols et al., Eur. Phys. J. A direct (2005) DOI: 10.1140/epjad/i2005-06-189-6 Island of Inversion MISTRAL: n-rich Na and Mg isotopes with high precision

  13. ISOLTRAP – triple trap spectrometer B = 6 T m c 1 B = 4.7 T 1 m m c 5 B u n c h e s , 3 k e V e n e r g y 6 0 k V I S O L D E - e 6 0 0 0 0 V i o n b e a m Linear RFQ trap PRINCIPLE determination of cyclotron frequency Mass measurement via determination of cyclotron frequency wc = (q/m)B coolingisobar separation accumulation & bunching of ISOLDE 60 keV beam G. Bollen et al., NIM A 368 (1996) 675 H. Raimbault-Hartmann, NIM B 126 (1997) 378 F. Herfurth et al., NIM A 469 (2001) 254 A. Herlert, K. Blaum

  14. ISOLTRAP harvest In 2002-2004 • 131masses measured () • rel. accuracydm/m1·10-7 • meanimprovement:factor40 232Ra 216Bi 147Cs 74Rb Highlights 2003 / 2004 72Kr Nuclide Half-life Uncertainty Yield 17Ne 109 ms ~300 eV ~1000/s 32Ar 70Cu 22Na 2.6 y 160 eV ~106/s 22Mg 98 ms 1.8 keV ~100/s 32Ar 33,34Ar 17.2 s 8.0 keV ~1000/s 72Kr 17Ne 65 ms 4.5 keV ~500/s 74Rb

  15. 32,33Ar - most stringent test of IMME M = a + bTz + cTz2(+ dTz3)? 32ArT1/2 = 98 ms Y=100/s 220 200 (ms) 180 160 Mean TOF 140 120 100 80 -40 -30 -20 -10 0 10 30 20 n - 2842679 (Hz) RF ISOLTRAP d / keV 33Ardm = 0.44 keV 32Ardm = 1.8 keV K. Blaum et al., PRL 91, 260801 (2003) A = 33, T = 3/2 quartet: Limits for Scalar Currents from b-delayed p-decay of 32Ar can now be put on purely experimental ground a = 1.0050 ± 0.0052(stat) ± (syst) Motivated by: d = -0.13(45) keV Search for Scalar Currents from b-delayed p-decay of 32ArE. G. Adelberger, A. Garcia et al., PRL 83 (1999) 1299 and 3101 A = 32, T = 2 quintet: d = -0.11(30) keV

  16. Towards exotic doubly magic nuclei - 78Ni BRAND NEW 81Zn ISOLTRAP Evolution of nuclear binding towards doubly-magic 78Ni is not known nuclear structure – r-process C. Guenaut PhD 2005EPJA direct 2005 Is N = 40 magic? More measurements are required! + n-rich tin isotopes up to 135Sn

  17. Identification of triple isomerism in 70Cu 101(3) keV 242(3) keV ISOLTRAP RILIS     Intensity ratio: 16% 80% 4%  (6–) state = gs  wc=q/m·B  (3–) state = 1.is  Unambiguous stateassignment! with cleaning of 6– state  1+ state = 2.is J. Van Roosbroeck et al., PRL 92, 112501 (2004)

  18. Mass measurement programs outside ISOLDE + reactions (unbound states, beyond the dripline) and decays New projects: TITAN at ISAC (highly-charged ions), MAFFTRAP (n-rich)

  19. SHIPTRAP – Towards SHE 147Ho BRAND NEW 146Ho(#), 147Ho, 147Er(#), 148Er(#), 147Tb, 147,148Dy, 148Tm(#) precision measurements with heavy ions produced at SHIP/GSI M. Block/GSI Fusion-evaporation reactions

  20. Low Energy Beam and Ion Trap Facility at NSCL/MSU 1 cm 1 cm Precision experiments at low-energies with rare isotopes from fast-beam fragmentation LEBIT ~ 100 MeV/u ~ 1 eV Gas stopping Low-energyexperiments 9.4 T Penning trap system Gas stopper Beam Buncher Mass measurements Laser spectroscopy Post Acceleration beam from A1900

  21. Precision Mass Measurement of Fast Beam Fragments T1/2 = 181 ms & … and more to come 37Ca++ 67As+ Secondary Beam 38Ca (92 MeV/u) m(38Ca++)/m(H30+) Statistical uncertainty dm  80 eV Expected final uncertaintydm < 300 eV • First successful nuclear physics experiment with a thermalized beam from fast beam fragmentation. • 38Ca is a 0+  0+ beta emitter: new candidate for CVC tests.

  22. Conclusions • Mass measurements are key to a better understanding of nuclear structure and important to other fields of research with radioactive isotopes • ISOLDE has a very strong mass measurement program • Experiments related to key topics: halos, evolution of shell structure, nuclear astrophysics, fundamental interaction tests • Two excellent experimental devices with significant development potential • Complementary programs exist worldwide– different techniques (PTMS, TOF, ESR) – different production methods … still a lot to be done!

  23. Mass Measurements at RIA Known masses PTMS dm < 50 keV TOFMS dm > 300 keV RIA-TRAP with 21 Tesla

  24. Masses close to Z=82 ISOLTRAP Region of shape-coexistence with interesting nuclear structure effects S. Schwarz et al., NPA 693 (2001) 533 Discussion within IBM & microscopic-macrosopic modelR. Fossion et al., NPA 697 (2002) 703

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