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Coulomb excitation with radioactive ion beams

Motivation and introduction Theoretical aspects of Coulomb excitation Experimental considerations, set-ups and analysis techniques Recent highlights and future perspectives. Coulomb excitation with radioactive ion beams. Lecture given at the Euroschool 2009 in Leuven Wolfram KORTEN

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Coulomb excitation with radioactive ion beams

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  1. Motivation and introduction Theoretical aspects of Coulomb excitation Experimental considerations, set-ups and analysis techniques Recent highlights and future perspectives Coulomb excitation with radioactive ion beams Lecture given at the Euroschool 2009 in Leuven Wolfram KORTEN CEA Saclay Euroschool Leuven – Septemberi 2009

  2. Coulomb Excitation of 20-21Na,21Ne 1st TIGRESS Experiment, Aug 2006 1x10cm collimator Bambino Θ = 20-50o plastic scintillator Pb shielding Euroschool Leuven – Septemberi 2009

  3. Properties of mirror nuclei 21Na/21Ne t(5/2+) = 1/ltot = [l(M1;5/2+3/2+) + l(E2; 5/2+3/2+)]-1 with I(M1) >> I(E2) with δ(E2/M1; 5/2+→3/2+) = -0.074(1) B(E2;3/2+5/2+) = 243 W.u. with δ(E2/M1; 5/2+→3/2+) = +0.05(2)  B(E2) = 1412 W.u. Euroschool Leuven – Septemberi 2009

  4. 21Ne, 21Na Heavy-ion gated γ-ray spectra • Clean γ-ray spectra with negligible influence of 511 keV due to intense beam β+ activity • For Ti Doppler correction shows both 46Ti and 48Ti 2+ decay transitions Euroschool Leuven – Septemberi 2009

  5. GOSIA analysis and results • γ ray yields of 5/2+3/2+ transition were measured in coincidence with θ and φ gates on the recoiling ions. • Matrix elements were fit to the measured yields using the GOSIA search code assuming the following level scheme. • Known lifetimes and branching ratios as input parameters [1] R.B. Firestone, NDS 103 (2004) 269 with NNDC 10/10/2006 erratum “Wrong” M1/E2 mixing  Stronger E2 component than previously reported Comprehensive Error analysis includes uncertainties in beam energy, target thickness, detector geometry (Clovers), unknown matrix elements and their signs, etc. Euroschool Leuven – Septemberi 2009 M.A. Schumacher et al., PRC78 (2008) 044321

  6. M. Girod Bruyères-le-Châtel R. Rodríguez-Guzmán, PRC 65, 024304 Shape coexistence in N=28 isotones Ca 40 96.94 Ca 42 0.65 Ca 44 2.08 Ca 48 0.19 Ca 50 13.9 s Ca 46 0.003 Rapid onset of deformation in N~28 nuclei below Ca ? 20 Ar 38 0.07 Ar 40 99.59 Ar 42 32.9 y Ar 44 11.9 m Ar 46 8.4 s Ar 48 0.48 s 18 All N=28 isotones predicted to show shape coexistence S 36 0.015 S 40 8.8 s S 42 1.01 s S 44 123 ms S 46 50 ms S 38 170 m 16 Precision measurement of e.m. matrix elements in 44Ar Si 34 2.77 s Si 36 0.45 s Si 38 >1 s Si 40 33 ms Si 42 13 ms Si 44 10 ms 14 Mg 32 86 ms Mg 34 20 ms Mg 36 3.9 ms Mg 38 >260 ns Mg 40 1 ms 12 20 22 24 26 28 30 Euroschool Leuven – Septemberi 2009

  7. Coulomb excitation set-up for RIBs (ex. SPIRAL) 16 large Ge Clover detectors 4  4 segmented photopeak efficiency  = 20% Double-sided Si detector 48 rings  16 sectors Euroschool Leuven – Septemberi 2009

  8. (6+) 3.439 (4+) 2.746 deep inelastic 44Ar + 208Pb cm=[67°, 130°] beta decay 2+ 1.158 2.977 2+0+ 2+0+ 1 1 1 1 2.748 (0+)2+ (0+)2+ (2+)2+ (2+)0+ 2 2 2 2 1 2 1 1 (2+) 2.011 0+ 2+ 1.158 0+ B. Fornal et al., EPJA 7, 147 (2000) J. Mrazek et al., Nucl. Phys. A 734, E65 (2004) Coulomb excitation of 44Ar at SPIRAL / GANIL 109Ag EXOGAM 44Ar + 109Ag cm=[35°, 72°] DSSD 44Ar SPIRAL beam 44Ar 3·105 pps 2.8·A MeV (Ag) 3.8·A MeV (Pb) 109Ag 208Pb Euroschool Leuven – Septemberi 2009

  9. The excitation cross section is a direct measure of the E matrix elements. b target projectile Im Mf If If If Ii Ii Ii 1st order: 2nd order: reorientation effect: Determination of quadrupole moments Sensitivity to Q2 by varying Z, q,(a,v) Euroschool Leuven – Septemberi 2009

  10. The excitation cross section is a direct measure of the E matrix elements. b target projectile Im Mf  If If If Ii Ii Ii 1st order: 2nd order: reorientation effect: • differential measurement of Coulomb excitation cross section •  extract both transitional and diagonal matrix elements •  B(E2) and spectroscopic quadrupole moment Qs • integral measurement is not sensitive to Qs • lifetime measurement  extract B(E2) independent of Qs Determination of quadrupole moments Euroschool Leuven – Septemberi 2009

  11. 4+ 4.067 Qs=+7 e fm2 Qs=14 e fm2 2+ 3.597 180 780 Qs=7.3 e fm2 +150 2+ 1.758 680 Qs=8(3) e fm2 -90 1.4 75 0+ theory HFB+GCM(GOA) Coulomb excitation of 44Ar at SPIRAL / GANIL Ag target, 35°cm70° Ag target, 70°cm130° Pb target, 30°cm130° • good agreement for B(E2) and Q • energy spectrum too spread out (4+) 2.746 2+ 2.011 2+ 1.158 4.6(8) 76(10) 0+ experiment B(E2;) in e2fm4 Euroschool Leuven – Septemberi 2009

  12. expected e.g. in: 74Kr 8+ 6+ 6+ 4+ 4+ 2+ 2+ 0+ 0+ 74Kr38 68Se34 72Kr36 70Se36 34 36 34 36 Shape coexistence around A=70 oblate prolate Possible 0+ shapeisomers and configuration mixing Euroschool Leuven – Septemberi 2009

  13. P2+ depends on • transitional matrix element B(E2) • diagonal matrix element Q0 • one measurement, • but two unknowns ! 2+ 0+ Coulomb excitation of 70Se at CERN / ISOLDE • 70Se on 104Pd at 2.94 MeV/u • integral measurement • excitation probability P(2+) via normalization to known 104Pd A.M. Hurst et al., PRL 98, 072501 (2007) (Univ. Liverpool)  (2+) = 1.5(3) ps J. Heese et al., Z. Phys. A 325, 45 (1986) ? Coulomb excitation probability (1) 68Se intermediate-energy Coulex GANIL E. Clément et al., NIM A 587, 292 (2008)

  14. Recoil-Distance Doppler Shift Method target and stopper foil at distance d gamma rays emitted • in flight  Doppler-shifted peak • at rest  narrow peak at E0 lifetime extracted from intensities as a function of distance d Euroschool Leuven – Septemberi 2009

  15. Heese et al. Ljungvall et al. Lifetimes in 70Se revisited Recoil-distance Doppler shift 40Ca(36Ar,2p)70Se beam GASP and Köln Plunger at Legnaro • literature value: = 1.5(3) ps • J. Heese et al., Z. Phys. A 325, 45 (1986) • new lifetime for 2+ in 70Se: = 3.2(2) ps J. Ljungvall et al., Phys. Rev. Lett. 100, 102502 (2008) 70Se 2+ 0+ shifted stopped

  16. Coulomb excitation of 74,76Kr at SPIRAL EXOGAM SPIRAL beams 76Kr 5105 pps 74Kr 104 pps 4.5 MeV/u Pb Acta Phys. Pol. B 36, 1281 (2005) Euroschool Leuven – Septemberi 2009

  17. [24°, 55°] [55°, 74°] [67°, 97°] [97°, 145°] 74Kr 4+  6+ 0+  4+  2+ 0+ 2+ 2+ 8+ Shape coexistence in 74Kr • 74Kr + 208Pb at 4.7 MeV/u (SPIRAL)  multi-step Coulomb excitation • -ray yields as function of scattering angle (differential excitation cross section) • experimental spectroscopic data (lifetimes, branching ratios) • least squares fit of ~ 30 matrix elements (transitional and diagonal) 0+ E. Clément et al., Phys. Rev. C 75, 054313 (2007) Euroschool Leuven – Septemberi 2009

  18. full 2 minimization: negative matrix element (positive quadrupole moment Q0)  prolate shape 74Kr positive matrix element (negative quadrupole moment Q0)  oblate shape Sensitivity to quadrupole moments 74Kr Euroschool Leuven – Septemberi 2009

  19. (4+ ) 2 oblate oblate prolate prolate  3.40 eb  0.86 eb + 3.13 eb + 2.11 eb +0.73 +1.30 +0.80 +1.22 -1.25 -1.30 -0.42 -0.60 + 5.07 eb + 1.85 eb + 4.66 eb + 2.50 eb +0.85 +0.80 +0.70 +0.80 -0.70 -0.79 -0.80 -0.80 2+ 2+ 6+ 0+ 2+ 0+ 0+ 6+ 0+ 2+ 4+ 4+ 2 1 1 1 1 2 2 1 1 1 3 1 Quadrupole moments (Q0) in 74Kr and 76Kr 74Kr 76Kr • direct confirmation of the prolate – oblate shape coexistence • first reorientation measurement with radioactive beam Euroschool Leuven – Septemberi 2009

  20. 4 diagonal E2 matrix elements • 5 diagonal E2 matrix elements Full results of Gosia analysis • 14 transitional E2 matrix elements • 18 transitional E2 matrix elements Euroschool Leuven – Septemberi 2009

  21. Experimental results and comparison with theory Qs<0 prolate Qs>0 oblate  vibration prolateoblate E. Clément et al., Phys. Rev. C 75, 054313 (2007) Calculation HFB-Gogny 5-dim GCM experimental B(E2;) [e2fm4] • complete set of e.m. matrix elements, incl. static moments • quantitative understanding of shape coexistence and configuration mixing • triaxiality is the key to reproduce experimental data and shape evolution Euroschool Leuven – Septemberi 2009

  22. Pd Zn Zn Coulomb excitation of 74-80Zn at Rex-Isolde 80Zn on 108Pd (2.87 MeV/u, 2.0 mg/cm2, 3000 pps) • Beam contaminants • increase for more exotic beams • must be taken into account when • calculating the target excitation J. Van de Walle et al., PRL 99, 142501 (2007) and PRC 79, 014309 (2009) Euroschool Leuven – Septemberi 2009

  23. Mf If Ii Coulomb excitation of 74-80Zn at Rex-Isolde Integral measurement  one observable: total excitation probability 74Zn 20 ps 25 ps 28.5 ps two unknowns: • B(E2) • Qs Life time measurements would reduce B(E2) errors and determine Q0 possible by using RDDS technique after multi-nucleon transfer reactions Euroschool Leuven – Septemberi 2009

  24. Employ high efficiency BaF2g-array ~ 40% full-energy at 4 MeV Use high-Z target (48Ti) Run at higher (“unsafe”) energies (495 MeV and 470 MeV) Limit distance of closest approach by looking only at forward angles in center of mass Coulomb Excitation of 132Sn at HRIBF • Opportunity to study a new doubly magic nucleus • Study collectivity of N=82, Z=50 core excitation • High E(2+) ~ 4MeV + small B(E2) + weak beam (104 pps)  very low event rate Euroschool Leuven – Septemberi 2009

  25. Setup for 132,134Sn Coulomb Excitation BaF2 array (150 crystals) for gamma-rays Beam courtesy of D. Radford Euroschool Leuven – Septemberi 2009

  26. Setup for 132,134Sn Coulomb Excitation “CD”-type Si detector for scattered Sn and Ti Beam • 7 cm diameter • 48 radial strips • 16 sectors • qLAB ~ 7° – 25° • qCM ~ 30° - 160° courtesy of D. Radford Euroschool Leuven – Septemberi 2009

  27. First results on 132Sn • 132Sn beam, doubly stripped • - 96% pure • - 1.3 x 105 ions/s • - 3.75 & 3.56 MeV/u • 48Ti target • High  efficiency (~ 40%) • Two-week experiment • Fast –ion coincidences • to suppress background Euroschool Leuven – Septemberi 2009

  28. Sample gamma-ray spectrum: • ~30% of data • Crystal gain matching & background suppression not yet optimum 48Ti 2+0+ 983 keV; 1.2 barns 470 MeV qcm < 110° 132Sn 2+0+ 4041 keV First results on 132Sn • 132Sn beam, doubly stripped • - 96% pure • - 1.3 x 105 ions/s • - 3.75 & 3.56 MeV/u • 48Ti target • High  efficiency (~ 40%) • Two-week experiment • Fast –ion coincidences • to suppress background Euroschool Leuven – Septemberi 2009

  29. Sample gamma-ray spectrum: • ~30% of data • Crystal gain matching & background suppression not yet optimum 48Ti 2+0+ 983 keV; 1.2 barns 470 MeV qcm < 110° 132Sn 2+0+ 4041 keV First results on 132Sn • 132Sn beam, doubly stripped • - 96% pure • - 1.3 x 105 ions/s • - 3.75 & 3.56 MeV/u • 48Ti target • High  efficiency (~ 40%) • Two-week experiment • Fast –ion coincidences • to suppress background B(E2; 0+2+) ~ 0.11(3) e2b2 R. Varner et al., EPJ. A 25, s01, 391 (2005) Euroschool Leuven – Septemberi 2009

  30. 132Sn: B(E2) ~ 0.11(3) e2b2 14% Isoscalar E2 EWSR 134Sn: B(E2) = 0.029(5) e2b2 E(2+) (keV) B(E2; 0+2+) (e2b2) A (Sn Isotopes) Coulomb Excitation Results for Sn isotopes New facilities needed in order to fully explore this mass region Euroschool Leuven – Septemberi 2009

  31. Coulomb excitation studies with low-energy RIBs • Drip lines and shell Structure in light nuclei • Drip-line nuclei: 10Be • Mirror nuclei : 20,21Na, 21Ne • The “island of inversion” : 29Na, 30,31,32Mg N=82 Z=82 N=50 N=40 Z=50 Z=28 20,21Na,21Ne 29Na,30,31,32Mg 10Be 20 Euroschool Leuven – Septemberi 2009

  32. Coulomb excitation studies with low-energy RIBs • Evolution of Shell Structure far from stability • 44Ar (N=28) • 68-78Ni (Z=28, N=40-50) : 68Ni, 67,69,71,73Ci, 68,70(m)Cu, 74,76,78,80Zn, 61Mn, 61Fe • 100Sn : 106,108,110Sn, 100,102,104Cd • 132Sn : (Z=50, N=82) 122-126Cd, 126-134Sn, 132-136Te, 140Ba N=82 Z=82 N=50 N=40 106,108,110Sn Z=50 122,124Cd, 126-134Sn 132-136Te, 138,140Xe 140,148,150Ba Z=28 74,76,78,80Zn, 82Ge 67,69,71,73Cu, 68Cu, 70(m)Cu 68Ni 20 Euroschool Leuven – Septemberi 2009

  33. Coulomb excitation studies with low-energy RIBs • Evolution of nuclear shapes and shape coexistence • N=Z 34: 70Se, 74,76Kr, • N 60: 88-94Kr, 96Sr • N 104: 182,184,186,188Hg, 202,204Rn 182,184,186,188Hg 202,204Rn N=82 Z=82 N=50 N=40 Z=50 74,76Kr 70Se 96Sr, 88-94Kr Z=28 20 Euroschool Leuven – Septemberi 2009

  34. 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 Perspectives Ho 67 165 Dy 66 Quadrupole deformation zone 164 Tb 65 159 Gd 64 146 160 Eu 63 153 Sm 62 154 Pm 61 Nd 60 150 Pr 59 141 102 Ce 58 142 La 57 Octupole deformation gaps  139 145 100 Ba 56 138 145 Cs 55 133 Xe 54 98 136 I 53 94 96 127 Te 52 130 Sb 51 123 Sn 50 92 124 132 In 49 115 Cd 48 88 90 116 Ag 47 109 Pd 46 110 62 64 66 68 70 72 74 76 78 80 82 84 86 Rh 45 103 Spherical robust gaps Ru 44 104 Tc 43 99 Mo42 100 Nb 41 93 Zr 40 90 96 Spherical fragile gaps 89 Y 39 Sr 38 88 98 100 Rb 37 87 Kr 36 86 Fission region Br 35 81 Se 34 82 As 33 75 Ge 32 76 Ga 31 Deformed gaps 71 Zn 30 70 Cu 29 65 Ni 28 64 78 courtesy D. Verney (IPNO) Euroschool Leuven – Septemberi 2009

  35. 96Kr 98Sr 44 M. Girod CEA Bruyères-le-Châtel 100Ru 102Ru 104Ru 106Ru 108Ru 42 96Mo 98Mo 100Mo 102Mo 104Mo 106Mo 108Mo 40 94Zr 96Zr 98Zr 100Zr 102Zr 104Zr 106Zr 100Zr 38 92Sr 94Sr 96Sr 98Sr 100Sr 102Sr 104Sr 36 90Kr 92Kr 94Kr 96Kr 98Kr 100Kr 102Kr 34 J. Skalski et al., NPA 617, 282 (1997) 90Se 92Se 94Se 96Se 98Se 54 56 58 60 62 64 66 Shapes in neutron-rich A=100 nuclei Euroschool Leuven – Septemberi 2009

  36. Coulomb excitation measurement towards 100Sn 106-108Sn+ Ni @ 2.8 MeV/u A. Ekstrom et al., PRL101 (012502) 2008 Euroschool Leuven – Septemberi 2009

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