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Estudio experimental de la Estructura Nuclear: Modos Exóticos de Desintegración

Estudio experimental de la Estructura Nuclear: Modos Exóticos de Desintegración. Mª José García Borge. Decay  + -EC Decay  - Decay  Fission. The Nuclear landscape. 256 stable nuclei. Incógnita. Terra. 4 o-o 157 e-e 104e-o. Near de Drip-line Halo structure

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Estudio experimental de la Estructura Nuclear: Modos Exóticos de Desintegración

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  1. Estudio experimental de la Estructura Nuclear: Modos Exóticos de Desintegración Mª José García Borge M.J.G. Borge, IEM, CSIC

  2. Decay +-EC • Decay - • Decay  • Fission The Nuclear landscape 256 stable nuclei Incógnita Terra • 4 o-o • 157 e-e • 104e-o Near de Drip-line • Halo structure • Re-ordering of shells gaps • Beta asymmetry • Exotic decays • Order to Chaos M.J.G. Borge, IEM, CSIC

  3. Ion source Mass Separator target Accelerator recoil. + ZAN γ γ β Z-1AN+1 γ Transport system Beta decay Studies M.J.G. Borge, IEM, CSIC

  4. + espalación F r 2 0 1 fragmentación + + U 2 3 8 L i X 1 1 fisión + + C s 1 4 3 Y Producción de Núcleos Exóticos p  1GeV n p M.J.G. Borge, IEM, CSIC

  5. Isotope Separator on Line @ CERN Target + Ion Source Energy:1 GeV (1.4 GeV) Pulse frequency: 1.2 s Intensity:3.2x1013 protons per pulse I (average):2 A Separator M.J.G. Borge, IEM, CSIC Firenze, 6 March 2006

  6. Nuclear Stability BE(A,Z) = ZMpc2 + NMnc2 – M’(AZXN)c2 Using the Bethe-Weizsäcker ec. for BE(A,Z) M’(AZXN)c2 = ZMpc2 + NMnc2 - avA + asA2/3 + acZ(Z-1)A-1/3+ aA(A-2Z)2/A - apA-1/2 For each A Parabolic behaviour with Z x = Mnc2 -av + aA + asA1/3 M’(AZXN)c2 = xA + yZ + zZ2+0() y = (Mp-Mn)c2 - 4aA- acA1/3 z = acA1/3 + 4aA/A Odd-A-impar  1 Stable nucleus  The rest  • Even-A 2 parabolas M.J.G. Borge, IEM, CSIC

  7. Short half-lives (10ms) • High Qb values • Low Sp/n values • Selection rules: • Fermi: DT=0 ;DJ=0 ; pf = pi • Gamow-Teller: DT=0±1; DJ=0±1; pf = pi • Reduced transition probability: Decay properties of exotic nuclei • 1916 Rutherford & Wood [Philos. Mag. 31 (1916) 379] • 1963Barton & Bell identified 25Si as p • Global properties -delayedparticle emission • Very Selective probe • Particle energy spectrum determined by 2 factors • 1-intensity of -decay branches from precursor to the emitter • 2-probability of emission by proton rather gamma M.J.G. Borge, IEM, CSIC

  8. In 33Ar  low level density, spectrum marked • for proton peaks • Cut off at low energy at the Coulomb barrier • IAS (only in precursors with TZ  -3/2) Emitter even-even QEC and Bp large  populate high excited states  rather smooth spectrum Emitter even-odd Bp low  proton emitted from low states  fluctuations more pronunced • Notice differences Beta Delayed Proton Emission (TODAY)Today more than 134 precursor known • Properties well understood • This spectroscopic tool is often the only way • to identify exotic nuclei • Data provide large spectroscopic information • Level density • Spin, isospin • Width & density • -decay properties IAS • In the rest bellshape spectrum with superimpose peak structure •  no individual transition rather cluster of them atributed to Porter-Thomas fluctuations M.J.G. Borge, IEM, CSIC

  9. 33Ar p-spectrum free of -summing 0 2 3 4 Ep (MeV) Electron-Neutrino Correlations (p emitters) The proton has info about the 32Cl recoil (Doppler) 32Ar Instead of detecting the neutrino 31S+p 32Cl • Study of the proton line shape • Physics beyond the SM • Isospin mixing in Fermi decays • Configuration mixing • Level interferences • Spin assignment • Excitation energies 32Ar 0 2.5 3.5 Schardt & Riisager, Z. Phys. A 345 (1993) 265 Adelberger & Garcia, Hyp. Int 129 (2000) 237 Ep (MeV) M.J.G. Borge, IEM, CSIC

  10. In-flight production allowed to extract very short species. Beams of 160, 36Ar, 40Ca, 58Ni,70Ge & 78Kr on secondary targets p, 2p in the sd-, pf-shell has been produced by fragmentation reaction at GANIL using the LISE-spectrometer Production of neutron deficient nuclei @ GANIL • 2p Radioactivity M.J.G. Borge, IEM, CSIC

  11. Experiment Theory Counts Energy (keV) Strong beta summing Analysis of -protons data 21Mg M.J.G. Borge, IEM, CSIC

  12. b+ : p→n + e+ +  d = 4.8 (4) % b- : n→p + e- +  E.C. : p + e-→n +  ft- ft+ n p n p Mirror Asymmetry & Systematics  = nuc + SCC Thomas et al., AIP Conf. Proc 681, p. 235 • Allowed Gamow-Teller transitions (log(ft)<6) • 17 couples of nuclei • 46 mirror transitions Average asymmetry d : 11 (1) % in the 1p shell (A<17) 0 (1) % in the (2s,1d) shell (17<A<40) M.J.G. Borge, IEM, CSIC

  13. T1/2 = (20.8 ± 0.3) ms Pp = (79.0 ± 2.7) % Spectroscopy of Neutron Deficient nuclei 22 < Z < 28 Spectroscopy studies wuth b-p-g, b-g • 23 isotopes Studied • Macroscopy Properties : T1/2, Pp • Spectroscopy: • Partial Decay scheme • IAS Identification • IMME M(A,T,Tz) = a() +b()Tz + c()Tz2 + 43Cr 43Cr M.J.G. Borge, IEM, CSIC

  14. Exotic Radioactivities 1p-radioactivity (Z,N)  p + (Z-1,N) 2p-radioactivity (Z,N)  2p + (Z-2,N) M.J.G. Borge, IEM, CSIC

  15. 1 Proton Radioactivity Proton-radioactivity from gs determine the limit for neutron deficient nuclei Qp = ( MZ+1 – MZ – mp – me ) c2 > 0 Qp = BEZ – BEZ+1 > 0 (Qp (151Lu) = 1241 keV) The observation of protons from 151Lu & 147Tm fixed the proton drip-line of this region (GSI, 1981) • Emission of protons only from odd-Z [50-83] • The sensitivity of T1/2 to angular momentum permit to assign the orbital from which the proton is emitted. • As protons are detected with high efficiency, proton emitters are used to identify nuclei in Recoil Decay Tagging (RDT). M.J.G. Borge, IEM, CSIC

  16. Known proton emitters Proton emitting from isomers and g.s. Fine structure in proton emitters Proton emitters known today In the 90´s explosion of information on proton radioactivity • Theoretical models are able to reproduce the systematic of p-decay spectroscopic factors for a wide range of spherical nuclei sensitive test of Shell Model at the edge of stability • p-emission from highly deformed nuclei has been observed and decay rates explained assuming Nilsson states 82 50 M.J.G. Borge, IEM, CSIC

  17. Direct two proton radioactivity • Predicted in 1960 [Vitali & Gol’danskii, Nucl. Phys. 19 (60)482;27(61)648] • General property of light nuclei with even number of protons (Z=10 to Z=50) close to the proton instability limit • Origin  pairing force • Easier to eject a pair of protons from a nucleus than to break the pair apart • If Bp,odd<0 • Bp,even=Epair+Bp,odd=Epair-|Bp,odd| • Bp,even>0  2p-radioactivity • 2p-radioactivity is a 3 body problem • Penetration through Coulomb barrier • lead to strong energy and angular • correlations • Interesting because the correlation between emitted protons can give yield information on the nature of their transition within and outside the nucleus Sp Bp,even Bp,odd Pairing Epp=|Bp,odd|-Bp,even S2p 2p Known: 6Be  2p +  p + 5Li (= 1.5 MeV)  p +  How does it decay? Z=2m+2 Z=2m+1 Z=2m M.J.G. Borge, IEM, CSIC

  18. Sp S2p S2p+S T1/2(ms) 22Si +1.10 +0.01 +0.01(?) 6(3) 31Ar +0.48 -0.23 -0.17 14.1(7) 39Ti +0.43 -0.79 -0.57 31.6(7) 42Cr +1.19 -0.69 -0.40 13.4-2.4+3.6 45Fe +0.07 -1.14 -0.82 48Ni +0.46 -1.35 -0.97 54Zn +0.40 -1.51 Direct Two-Proton Emission Candidates • The discovery of direct g.s. 2p-decay has been hampered by • 1-the stringent energetic requirement (Sp>0, S2p<0) • 2-need to detect low energy protons (in light nuclei, coulomb barrier low) • Use of the Garvey and Kelson mass formula for mirror nuclei [Phys. Rev. Lett 16 (1966) 197] • Assumption: charge symmetry of nuclear forces • Independent particle picture • Accuracy in M200 keV • Correction by Thomas Ehrmann Shift effect S (negative separation energy for the unbound individual particle state). S = (0.28(9))xS (where S is Sp>0 or S2p < 0) • Comay, Kelson &Zidon[ADNDT 39(1988)251] Candidates for 2p radioactivity M.J.G. Borge, IEM, CSIC

  19. Giovinazzo et al., PRL 89 (2002) 102501 M.J.G. Borge, IEM, CSIC

  20. Giovinazzo et.al. Phys Rev Lett. 89(2002)102501 M.J.G. Borge, IEM, CSIC

  21. 57(6) % 2p E2p = 1.154(16) MeV Status of 2p-radiaoctivity GANIL Fragmentation reactions 58Ni-beam 45Fe 45Fe Giovinazzo et al., PRL 89 (2002) 102501 Agreement with 3-body model for p-wave emission Dossat, PRC, submitted • Next Steps: • Search for new two-proton emitters • 48Ni , 59Ge ….. • Detailed study of the decay process Measurement of proton-proton correlation: • p-p angle • Individual proton energies • Modelling of the 2p resonance 87(13) % 2p E2p = 1.48(2) MeV 54Zn 54Zn Blank et al., PRL 94 (2005) 232501 M.J.G. Borge, IEM, CSIC

  22. Q = 18.5 MeV An Exotic Nucleus: Z=18, N=13 M.J.G. Borge, IEM, CSIC

  23. Emisión retardada de 2-protones Predicho en 1980 [Goldanskii, JETP Lett. 32 (1980) 554] • 3 modos de desintegración: • Emision secuencial. • E1, E2 ind. Picos, E2 ensanchado por retroceso • Emisión casi isótropica Emision di-protonica • E1E2, anchos • Gran correlacion angular Emision democratica • E1E2, anchos • Cierta correlacion angular M.J.G. Borge, IEM, CSIC

  24. Experimento 1995 M.J.G. Borge, IEM, CSIC

  25. Experimento 1997 Yield 2 atom/s Solid angle 14 + 11 % e1p 23.7 % e2p 5.2 % e3p 1.3 % M.J.G. Borge, IEM, CSIC

  26. IAS 2p/1p (IAS) 9 31Ar @ the dripline: 18p + 13n Unique Spectroscopic Information Q2pEIAS = 12322(2)(50) keV QEC = EIAS + Ec - np Ec =7045 keV QEC = 18490(110) keV f(EIAS)tIAS = 6145(4) s / [B(F) + B(GT)] b.r.(IAS) = T1/2 / tIAS B(F) = [T(T+1)-TziTzf ]if= 5 Expected b.r. (IAS) = 4.35(31)% Experimentally: b.r. (IAS) = 4.25(30) % M.J.G. Borge, IEM, CSIC

  27. b-delayed 2p emission from 31Ar 1 M.J.G. Borge, IEM, CSIC

  28. Decay of IAS through 2p emission Diagonal from decays via single intermediate state from many initial states fed in beta-decay 1p-spectrum. 31Ar -2p emitter 2p-spectrum M.J.G. Borge, IEM, CSIC

  29. Gamow-Teller 2p-transition Isospin allowed transitions increasing # of intermediate states possible • Kinematics of sequential emission • 2He branch present at some level ? 1st emitted 30S* 29P 2nd emitted M.J.G. Borge, IEM, CSIC

  30. Deuterio 6Li 7Li 8Li 9Li 11Li Tanihata, 1985 ¿Why isthe mass radius so large? Surprise at the neutron drip line 1985, First experiments with radioactive nuclear beams, Berkeley (USA) Be, C and Al Tanihata 11Li R(11Li) = 3.30(24) fm M.J.G. Borge, IEM, CSIC

  31. Experimental Studies at the drip line Elastic Scattering Spins Moments Reaction Cross Sections Masses Beta Decay Momentum Distributions Unbound Nuclei M.J.G. Borge, IEM, CSIC

  32. Even a neutron rich - nuclei emit charged particles! 20.6 - 3/2- 1996 17.916 T1/2 = 8 ms 1983 9Li+d 1966 9Li 15.721 8Li+t 10.59 p 1980 d 8.82 8.982 1979 2+3n 7.315 9Be+2n 0.320 ½- 1974 Energías (MeV) g 0.504 0.320 ½+ 10Be+n 11Be 11Be Beta decay of an exotic nuclei M.J.G. Borge, IEM, CSIC

  33. Qd = 3.007 – S2n MeV M.V. Zhukov et al., PRC47 (1993) 2937 D. Baye et al., Prog. Th. Phys. 91 (1994) 271 F.C. Baker, Phys. Lett. B 322 (1994) 17 Beta-delayed deuterons b- 6He a+d M.J.G. Borge et al., Nucl. Phys. A560 (1993) 664 Anthony et al., PRC 65 (2002) 034310 10-4 6Li Intensity (decay-1 MeV-1) 10-5 10-6 Exploring w.f.  10 fm 500 1000 0 0 Ed (keV) M.J.G. Borge, IEM, CSIC

  34. 11Li, gamma rays 320 keV ½- g ½+ 11Be Q = 20.62 MeV, T 1/2= 8.2 ms b(320) = 6.3(6) % log ft = 5.73 M.J.G. Borge et al., PRC55 (97) R8 N. Aoi et al., NPA616 (97) 181c D. Morrisey et al., NPA627 (97) 222 (1s1/2)2/(0p1/2)2 ~1 M.J.G. Borge, IEM, CSIC

  35. 11Li (284 MeV/u) + C 9Li + n @ GSI H. Simon et al., PRL 83 (1999) 496 10Li 10Li 9Li n2 n1 (1s 1/2)2 = 45(10) % in the 11Li g.s Single-particle momentum distributions, Hankel functions M.J.G. Borge, IEM, CSIC

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