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Coulomb excitation at intermediate energies

Instituto de Estructura de la Materia – Consejo Superior de Investigaciones Científicas. Coulomb excitation at intermediate energies. Andrea Jungclaus. Instituto de Estructura de la Materia, CSIC

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Coulomb excitation at intermediate energies

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  1. Instituto de Estructura de la Materia – Consejo Superior de Investigaciones Científicas Coulomb excitation at intermediateenergies Andrea Jungclaus Instituto de Estructura de la Materia, CSIC Madrid - Spain Au target Coulomb total nuclear

  2. Coulomb excitation Winther & Alder Nucl. Phys. A 319, 518 (1979) Alder & Winther ElectromagneticExcitation North-Holland, 1975 courtesyKathrinWimmer

  3. Coulomb excitation Toeliminate nuclear excitations: Choosebeamenergy in the "safe" regime(<5 MeV/u): Low-energy Coulomb excitationusedwithradioactivebeams at REX-ISOLDE, ISAC-II and SPIRAL Restrictthescatteringangleorequivalent theminimumimpactparameter: "touchingspheres + 2 fm" Interactionisthenassumedto be purelyelectromagnetic !

  4. Measurement ofscattering angle RIKEN 2 PPACs in front of and 1 PPAC behindthe target TPC and target DSSD in front ofand wallDSSD of LYCCA behindthe target PreSPEC

  5. Typical angular resolutions V.M. Bader et al. Phys. Rev C88, 051301(R) 136Te @ 165 MeV/u on 950 mg/cm2Au RIKEN 102Cd @ 73MeV/u 184 mg/cm2 Au s=4.8 mrad sstr= 9.1mrad s=5.4 mrad NSCL s=8.8 mrad sstr= 8.1 mrad 46Ti @ 178 MeV/u 500 mg/cm2 Au PreSPEC V. Vaquero et al., Phys. Rev. C 99, 034306 (2019) sstr=5.9mrad s2= s2meas + s2str s=1.8 mrad Allmeasured angular resolutions are quite similar, but ... A. Boso, PhD thesis

  6. Angular resolution versus "safe" angle At beamenergiesaround 150 MeV/u (RIKEN,GSI) and maximumscattering anglesaround 1.0-1.2º (17-21 mrad): Theapplication of anangularcutisnot reasonable! 136Te @ 139 MeV/u Qmax= 1.2º mid-target touchingspheres + 2 fm 88Kr @ 58.5 MeV/u Qmax= 3.2º mid-target At lowerbeamenergies (MSU) and larger maximumscatteringangles: Asafecutmaybe applied, but at thecost of loosingstatistics ! At energiesaround 150 MeV/u nuclear excitationshaveto be takenintoaccount !

  7. Angular resolution versus "safe" angle At beamenergiesaround 150 MeV/u (RIKEN,GSI) and maximumscattering anglesaround 1.0-1.2º (17-21 mrad): Theapplication of anangularcutisnot reasonable! 136Te @ 139 MeV/u Qmax= 1.2º mid-target touchingspheres + 2 fm 88Kr @ 58.5 MeV/u Qmax= 3.2º mid-target At lowerbeamenergies (MSU) and larger maximumscatteringangles: Asafecutmaybe applied, but at thecost of loosingstatistics ! B. Elman et al., Phys. Rev C 96, 044332 (2017) At energiesaround 150 MeV/u nuclear excitationshaveto be takenintoaccount !

  8. Coupledchannelsdistortedwavecalculations Requiredinput for FRESCO or ECIS: - opticalpotential (parameterizedormicroscopic) - nuclear deformationlengthdn - electromagnetcmatrixelement M(pl) I.J. Thompson, Comp. Phys. Rep. 7, 3 (1988); http://fresco.org.uk (versionmodifiedby A. Moro) 72Kr @ 164 MeV/u onAu Strongabsorptionautomatically takenintoaccount. Coulomb Interferencebetween Coulomb and nuclear excitations. total Angular cutisnevera really goodchoice! nuclear

  9. Coupledchannelsdistortedwavecalculations 46Ti @ 171 MeV/u onAu qmax dn=dc calculationfolded withs =7 mrad Coulomb total qmax nuclear scoul= 140mb snucl = 64 mb stotal = 160 mb

  10. Warningsconcerningothercodes DWEIKO: - uses straight-line approximation of Alder-Winthertheory C.A. Bertulani et al., Comp. Phys. Com. 152, 317 (2003) C.A. Bertulani, Comp. Phys. Com. 152, 317 (2003) FRESCO DWEIKO Wrongdescription of interference and absorption ! ECIS: - coupledchannelsusingstandardAlder-Winthertheory - Convergenceissueswhenusedfor heavy beams (seemtodepend onthetotal energy of thereaction, ok for light beams) J. Raynal

  11. A Coulexanalysisstepbystep: The caseof136Te Z Z ZeroDegree BigRIPS A/q A/q

  12. A Coulexanalysisstepbystep: The caseof136Te 1) Determine differentialcrosssectionson light and heavy targets. Sortspectrafordifferentscatteringanglebins and determine intensities: Au Au C C Correctfor ZD transmission and reactionlosses ! V. Vaquero et al., Phys. Rev. C 99, 034306 (2019)

  13. Transmission andreactionlosses Effective ZD transmission LYCCA wall DSSD 1o includesreactionlosses Efficiency as function of qlab ? Reactionlosses ?

  14. Reactionlosses in beam detectorsandtarget PreSPEC 2+ 0+ 52Fe on 400 mg/cm2 Au Dopplercorrectionassuming emissionfromtarget, startToF and target DSSSD, respectively. 52Fe Thereis a lot of material in the beam line, notonlythe target !

  15. A Coulexanalysisstepbystep: The caseof136Te 2) Determine total crosssectionson light and heavy targets. 136Te52+ Au C 136Te51+ sCtot= 23(3) mb FRESCO sAutot= 279(22) mb dn = 1.05(7) fm ZD transmission and reactionlosses

  16. A Coulexanalysisstepbystep: The caseof136Te 3) Compare foldedtheoretical curve with experimental distribution (C target). dn = 1.05(7) fm C target calculation calculationafterfolding withexp. resolution 4) CorrectsAutotforunobservedfeeding(in the case of the 2+ in 136Te 15(5)%). 5) In FRESCO adjustM(pl) to reproduce thecorrectedsAutotusingthevalue of dndeterminedabovewiththe C target.

  17. Makesurethatthefoldingiscorrectlydone ... 1D: ds(qlab) smearedwithGaussians 2D: Couplingbetweenscattering and stragglingvectors (thetwof are independent !).

  18. A Coulexanalysisstepbystep: The caseof136Te 6) Compare foldedtheoretical curve with experimental distribution (Au target). calculation Au target Coulomb calculationafterfolding Not a fitto data ! total nuclear scoul= 224 mb Onlyweakdependenceondndue tothedestructiveinterference ! snucl= 44 mb stotal= 219 mb

  19. A Coulexanalysisstepbystep: The caseof136Te 7) Evaluation of uncertainties. errorsontransmission, #gamma fromfit, number of ions, target thickness, downscale factor Purelystatistical error<1% ! B(E2)=0.191(26) e2b2 13.6% error Difficultto determine B(E2) withhigherprecision !

  20. Last comment: Can isomericstatescauseproblems ? Twodifferentsources of 2+ 0+grays: Eg T1/2 6+ • Decay of 2+statefollowinginelasticexcitation. 4+ • Decay of 2+populated in theisomericdecay. 2+ isomeric decays inelastic excitation b~0.5 v = 15 cm/ns 0+ Isomericdecayscontinuouslyduringtheflightthrough DALI Contamination of the 2-0 lineshape ! Quantitiestotakeintoaccountin theestimation of theeffect: • isomerhalf-life • isomeric ratio • energy of isomerictransition • inelasticexcitationcrosssection In most cases not a problem, butmakesure !

  21. Summary: CoulexanalysisandnewCoulexproposals Analysisprocedurefor Coulomb excitationexperiments at beamenergies around 150 MeV/u revised and checkedwithhigh-statistics data on136Te. V. Vaquero et al., Phys. Rev. C 99, 034306 (2019) Correct and wronganalysismay lead to similar resultsduetocancellation of effects. Doesthisjustifyto do itwrongly? Approachcan/shouldbe usedforcountrateestimatesforfutureproposals. Difficult (impossible ?) to determine B(E2) valueswithuncertainties below 15%. Makesurethatthisissufficienttoanswerthephysics questionyouwouldliketotackle (i.e. todistinguishbetweendifferent theoreticalpredictions). Makesurethat in the case of interestisomericdecays do notaffect theanalysis. ThankstoVictor, Kathrin and Pieter !

  22. FRESCO versus DWEIKO J. Barrette et al., Phys. Lett. B 209, 182 (1988)

  23. The resultfor136Te

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