1 / 29

María José García Borge Instituto de Estructura de la Materia, CSIC

β -delayed proton Emission: Peering into Nuclear Structure. Beta- delayed particle Emission studies and its Future @ MYRRHA. María José García Borge Instituto de Estructura de la Materia, CSIC. Beta delayed particle emitters. Close to 400 nuclei emit delayed particles

chelsey
Download Presentation

María José García Borge Instituto de Estructura de la Materia, CSIC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. β-delayed proton Emission: Peering into Nuclear Structure Beta-delayedparticleEmissionstudiesanditsFuture @ MYRRHA María José García Borge Instituto de Estructura de la Materia, CSIC

  2. Beta delayed particle emitters • Close to 400 nuclei emit delayed particles • Exotic decays @ drip line Qβd = 3.0 – S2n (MeV): 6He,11Li, 14Be, 17B, 19B, 22C Qβt = 9.3 – S3n (MeV): 8He,11Li, 14Be, 17B, 19C, 20C Qpα ó Qαp : 9C, 130, 17Ne, 23Si B.Jonson & K. Riisager, NPA693 (2001) 77 M. J. Gª Borge, IEM, CSIC, Madrid

  3. Short half-lives (ms) • High Qb values • Low Sp/n values • 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 Fermi Strengthindependentof Nuclear Structure E,  Level density Spin, Isospin -decay properties Gamow-Tellerstrengthobeysthe Ikeda sumRule M. J. Gª Borge, IEM, CSIC, Madrid

  4. Neutron Rich Beta-delayedNeutronemitters Compilationforfissionproducts 26 < Z < 58, Pfeiffer, Kratz, Möller, Porg. Nucl. Energy 41(2002)39 Kratz-Hermann formula Pn≈a[(Qβ–Sn)/(Qβ– C)]b Where C istheparameterofpairing, dependingofevenoroddcharacterofdaughternucleus About 220 cases measured, Mainly T1/2 andPn-values Spectroscopyhampered by detectionsystem! a b regr a b χ2

  5. DetectionMethods • 3He-spectrometers.Energyup to 2 MeV • Low efficiency≈ 10-3 • 4π –Counter • efficiency≈ 30 % • Dependingofdecaypattern • Time-of-Flight • Energymeasurement≈ 500-4000 keV • Difficulttohandlethe background Azuma et al., PRL43 (1979) + Digital electronicslowerthreshold M. J. Gª Borge, IEM, CSIC, Madrid

  6. Proton number N=50 Z=50 Qβ – Sn <0 Neutron number The Versatile Array of Neutron Detectors at Low Energy Beta-delayed neutron emitters near r-process path studied at the HRIBF/LeRIBSS in February 2012 • VANDLE • 2 clovers, 3% efficient @ 1MeV • 48 x 60 cm VANDLE bars • 45% efficiency/bar @ 1MeV • Ω = 26% of 4π • 12% total efficiency @ 1MeV • Fully instrumented using XIA’s Pixie 16 digitizers n-Sensitivitybelow 100 keV Courtesyof M. Madurga M. J. Gª Borge, IEM, CSIC, Madrid 77Cu (βn)

  7. 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 1974 Energías (MeV) 0.504 0.320 10Be+n 11Be Beta decay of an exotic nuclei Talk by Pierre descouvemont M.J.G. Borge, IEM, CSIC, Madrid (Spain)

  8. 11Li Polarized radioactive beams: 11Li @ TRIUMF 8.8 8 3/2 7 6.179 3/2 11Be 5 5.958 Neutron- 2590KeVγ-line 2.6 MeV 3.4 MeV 10Be • Spin polarized 11Li beam • , n, --n coincidences • Spin and parities of 7 levels in 11Be assigned. Hirayama, Phys. Lett. B 611 (2005)239 M. J. Gª Borge, IEM, CSIC, Madrid

  9. 11Be 10Be Energy, spin & T1/2 from -lines shape • In a βnγprocesstheshapeofbroadγ-linedependsof • Theenergylevel in 11Be, • Spin sequence • Lifetime ofn-fedstate T1/2(5.96 MeV)=50-60 fs. 61.5(17) fs Fynbo, NPA 736 (2004) 39 11Li Mattoon, PRC80 (2009) 034318 8.8 3/2,5/2 8 5.958 2+ 2.6 MeV 2+ 3.4 MeV M. J. Gª Borge, IEM, CSIC, Madrid

  10. 7 x BC501 Liquid scintillator 15 cm x 30 cm Ge 1.2m 2m g 3m • Gamma detection • 3 Glover (4xHPGe) Universal set-up for spectroscopy studies Set up: Cube of DSSSD 4-6 Segmented HPGe Good scheme for Neutron detection Fast Scintillators for T1/2 Neutron Detection Need to be improved!! M.J.G. Borge, IEM, CSIC, Madrid (Spain)

  11. Charged particle emission in the 11Li-decay • Current knowledge: • Four decay channels • Two states in 11Be: 10.6 and 18.3 MeV. • Theory: SM predicts B(GT) strength distribution peaks between 15 and 20 MeV. • Experiment:  doppler broadening suggests significant (6%) feeding of states in this region. T. Suzuki and T. Otsuka, PRC 56(1997)847 H.O.U. Fynbo et al., NPA736 (2004)39 M. J. Gª Borge, IEM, CSIC, Madrid

  12. Analysis techniques Energy & momentum conservation Momentum reconstruction Excitation energy of the 1-2 system: 11Li Beam 6He++n 60 g/cm2 • Deadlayer and carbon-foilenergy losses corrected • -background subtraction: • Efront- Eback40 keV Monolithic detector M. J. Gª Borge, IEM, CSIC, Madrid

  13. Charged Particle Coincidences M. Langevin et al., NPA 366(1981) 449 127º - 180º D2 D4 ED2+ED4 M. J. Gª Borge, IEM, CSIC, Madrid

  14. E11Be Q1 Q2 E’ 6He++n Evidence of decay through the 7He resonance 8.33 7.91 7He(gs) d  10 cm 2005 127º - 180º • Contribution of a new decay channel. • Contribution of a state at 16.3 MeV ( 1MeV) ). In agreement with theoretical expectations and previous -experiment 2007 d  8.5 cm M. J. Gª Borge, IEM, CSIC, Madrid

  15. Kinematic identification of βt emission in 11Li Qβt = M(11Li) - M(8Li) - M(t) = 4822(5) keV • Measurement in otherprecursors • Therelationwiththestructureoftheemittingnucleusislessunderstood. • Decaydirectlytothecontinuum? Madurga et al., Eur. Phys. J A42 (2009)415 11Li • Kinematicsnear 180º betweenchargedparticles. • 9Li+dchannelstopped, 9Li toolowrecoilenergy. • The8Li+tchanneluniquelyseparated  P2 M. J. Gª Borge, IEM, CSIC, Madrid

  16. B(GT) Distribution for 11Li from theory Shell model in s and pdshells G. Martinez-Pinedo, PhDthesis, UAM, 1995; M.J.G. Borge et al, PRC 55(1997) R8 H.O.U. Fynbo, NPA736(2004)39; Y.Hirayama , PLB611(2005)239 Experimental bias favors 3/2- detection in the 7He+ channel

  17. Beta-proton emitters • More than 160 precursors identified • For every element up to Z = 73 at least one proton precursor • The βp spectrum depends on the Z and A of the precursor and differs in the different mass region due to diferences in level density in the Q-Sp window • Properties of βp well understood largevarietyofspectroscopicinformation • For light nuclei with Z ≥ 8, the IAS within the Qec window. • From βp energy of IAS, QEC-Sp deduced. • Test Isobaric Multiplet Mass eq. M(A,T,Tz) = a + bTz +cTz2 + (dTz3+eTz4) • If strength to IAS  BF  Isospin Mixing • If IAS in the middle of the QEC large part of the GTGR available => quenching factor deduced M. J. Gª Borge, IEM, CSIC, Madrid

  18. Experiment Theory Counts Energy (keV) Strong beta summing Beta decayof21Mg 21Mg M. J. Gª Borge, IEM, CSIC, Madrid

  19. Quenching factor of GT-transitionsdeduced 33Arβppγ 32Ar 33Ar Z.Phys. A332(1989)413 Large angular coverage. Highefficiencyforbothprotonand gammas Quenching factor for Ar’s close to one, sensitive to the placement of the GTGR ΣBGT(experiment) Comparisonfor resolved protongroups theory theory Thequenching factor qdependsifone uses individual transitions 0.49(4) or full distribution. Adimi et al., PRC81(2010) 024311 ΣBGT(theory) q = 0.50(5) q=0.58(5) M. J. Gª Borge, IEM, CSIC, Madrid

  20. βνcorrelationstudies: peeringinto Nuclear Structure βνcorrelationdependsofthetypeofthetransition Importantprobeofthenatureofweakinteraction Theprotoncarriesinfooftherecoilingnucleus at the keV scale Ifthedecayisfollowed by particleemission, therecoilofthedaughtershiftstheenergyofthedelayedparticle by about 10 keV thatitiseasytomeasure. Firstusedtodeducedthenatureofthedecayofβ2αemitter8Li (A,Z) Z > A/2 p (A-1, Z-2) • Spins: 31Ar • Fermi / GT character • Intrinsicwidthsoflevels • Final state (gs/excited) ofdelayedparticle β–νcorrelationsallowtoextractspectroscopicquantities (A, Z-1) María José Gª Borge, IEM, CSIC, Madrid

  21. Search for New Physics • Set-up to avoid -summing @ ISOLDE p 32Ar 3.35 MeV +p e+ 5.1 MeV 32Cl 31Sl MSU 370 eV  100 keV p • The V-A character of -decay determined by measuring e- correlation [Johson,PR132(63)] • If p emitter  measurement of e- correlation from the broadening of proton peak from IAS • Isospin mixing in Fermi decays • Limit for scalar component in beta decays • MS ≥ 4.1 MW ISOLDE 32Ar 2 3 4 MeV • Absolute branching ratios /MSU • Very precise T1/2 determination /ISOLDE • ft = 1552(12) s for the Fermi decay • Isospin Symmetry breaking Correction • c = 2.0(4) % 0 2.5 Bhattacharya et al., PRC77 (2008) 065503 3.5 Ep (MeV) M.J.G. Borge, IEM, CSIC, Madrid (Spain)

  22. Mapping of Neutron Deficient nuclei 22 < Z < 28 Spectroscopystudieswithb-p-g, b-g • 23 isotopes Studied • MacroscopyProperties : T1/2, Pp • Spectroscopy: • Partial Decayscheme • IAS Identification • IMME Dossat et al., NPA702 (2007) 18 43Cr β2p + β3p observed. 12 % feedingtoboundstates Pomorski PRC 2011 β2p ? 46Mn M. J. Gª Borge, IEM, CSIC, Madrid

  23. Frompeaksto continua (Hardy, Cargese, 1976) • βpexploredhighexcitationenergy in thedaughter => individual transition are notlonger resolved ✔Tofittheprotonspectrum average oftheabovequantities are considered. (Z,N) • βp + X-Ray ratio stronglyconstrainttheleveldensitydistribution • Goodestimateofprotonand gamma widthsforexoticnucleiofinterestfornucleosynthesis • The Porter Thomas distributionaccountsofthefluctuationsobserved in thespectrum Qβ+ (Z-2,N+1)+p QEC Sp (Z-1,N+1) Giovinazzo et al, NPA674 (2000) 394 M. J. Gª Borge, IEM, CSIC, Madrid

  24. β-delayed 2p-emitters 9 β2p emittersidentified Mostofthe cases onlytheemissionfromthe IAS identified. Thedecay has beenidentified as sequential in thefew cases where 2p-emission has beenstudied in detailed: 22Al, 26P, 31Ar, 45Fe, 43Cr β-3p finallyidentified in 45Fe & 43Cr Characterizationofstatesnearparticlethresholdofastrophysicalrelevance. 31Ar remains as theeasier case tosearchforp-pcorrelationsduetoproduction. Study27S veryinteresting: Too lowβpandβ2p, Eur. Phys. J. A12 (2001) 377 β3p β3p M. J. Gª Borge, IEM, CSIC, Madrid

  25. 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. Gª Borge, IEM, CSIC, Madrid

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

  27. 31Ar: a new look 5/2+ 5,21 MeV β-2p protonspectrumexcitedunboundstates in 30S Fynbo et al., NPA A677 (2000) 38 p1 MirrorNucleus Astrophysical interest : The29P(p,)30S reaction rate depends of the 4.5-5.5 MeV states in 30S 5217 In previouswork, the 5.136 keV statewasfirstassign as 0+or 3+. Andrecently as 4+ María José Gª Borge, IEM, CSIC, Madrid

  28. Study 30S levels from 31Ar decay 5,21 MeV 8 30S Our β2p decaysmainlypopulate a level at 5217.4(7) keV thatdecayto 29P ½+ by 600 keV. Thepenetrabilitieswerefor 600 keV proton L= 0 P = 8.7 x 10-4 L = 2 P = 2.5 x 10-5 L=4 P = 6.7 x 10-8 5217 3+ 4+ Pγ-spectrum The 3+state in 30S alsoidentified inreactionwork. Setoodehnia et al. PR C82 (2010) 02280 : 32S(p,t)30S PR C83 (2011) 018803: 28Si(3He,nγ)30S Spin of 5.1 & 5.2 MeVlevelsdeducedfromparticlepenetrability Beta-decaystudytheonlyopportunityto determine thestateproton/gamma width 2210 1193 2477 3405 1406 2921 L=4 imposible M. J. Gª Borge, IEM, CSIC, Madrid

  29. Exotics decays: Nature of βt new condidates: 14Be…(10-4) Use ofPolarisedbeam. Angular correlationsstudies Mappingthechangeofstructure in theβpspectrumfrompeakstocontinuum DeterminationofΓΥ / ΓandΓporΓα / Γofastrophysicalrelevance β2p should be explored in detail in othercandidatesmainly27S and35Ca Searchforp-pcorrelation in excitedstate Summary & Outlook @ MYRRHA Particle emission studies done with high precision are an unbeatable probe of nuclear structure at the microscopic level M. J. Gª Borge, IEM, CSIC, Madrid

More Related