Beta-delayed Charged particles : Peering into Nuclear Structure

Transcription

1 Nuclear xperimental Beta-delayed Charged particles : Peering into Nuclear Structure aría José García Borge Instituto de structura de la ateria, 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 1

2 Nuclear Landscape Nuclear xperimental Desintegration β + -C Desintegration β - Desintegration α Proton Drip Line + Fission Fission 3000 nuclei known ost β ± -decay towards stability, others α-decay or fission Halo Nuclei Neutron Drip line Near the drip lines xotic decays Asymmetries Order to Chaos 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 2

3 J π i A(Z,N) I Nuclear xperimental β +,C β-decay process J = 0,±1, T = 0,±1, π i = π f στ Gamow-Teller J π f A(Z-1,N+1) τ Fermi J = 0, T = 0, π i = π f BGT 2 p 1/2 1 f 5/2 1 f 5/2 2 p 3/2 2 p 3/2 28 στ, Gamow-Teller 28 β ± -decay gives first glance on the structure by the half-life 1 f 7/2 1 f 7/2 Detailed spectroscopy gives the microscopic structure = ψ f στ ± ψ i 2 τ, Fermi BF = ψ f τ ± ψ i 2 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 3

4 Nuclear xperimental Production of xotic Nuclei Layout of GANIL Low energy beam line ISOLD Low energy beams Good Optics Chemical separation means In-Flight ethod Short separation times Direct determination of B.R. High efficiency due to deep implantation on detectors Simultaneous easurement of several nuclei 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 4

5 Nuclear xperimental Decay properties of exotic nuclei Global properties Short half-lives ( ms) High Q β values Low S p/n values β-delayed particle emission 1916 Rutherford & Wood βα [Philos. ag. 31 (1916) 379] 1963 Barton & Bell identified 25 Si as βp β + (C..) emission β-delayed particle spectrum depends: beta-feeding to the unbound levels in emitter Probability to emit the charged particle Reduced transition probability: ft = f * T 1 / 2 B. R. = 2 2 K 2 G V τ + G A στ 2 = B(F) C + B(GT), Γ Level density Spin, Isospin β-decay properties 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 5

6 Nuclear xperimental Beta delayed particle emitters B.Jonson & K. Riisager, NPA693 (2001) 77 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 6

7 Nuclear xperimental Powerful Source of Nuclear Structure Information xperiment 21 g Theory Coun ts IAS β-delayed proton spectrum gives level information in a broad energy range Impressive reproduction of the excited structure and B GT distribution by Shell odel calculation xtraction of the quenching factor of the axial-vector coupling constant 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 7

8 Nuclear xperimental vectorial Search for New Physics IAS escalar 32 Ar e-ν correlation a good probe of weak interactions The V-A character of β-decay determined by measuring e-ν correlation through the daughter recoil in 1963 Improved precision to find new physics by using βp emitter. e-ν correlation determined from the broadening of proton peak from IAS in transitions Supersymmetry and odels with lepto-quarks predicts scalar contributions to the weak interactions. V e.1 5 e + 32 Cl ν 370 ev 31 S p 3.35 ev 100 kev Isospin mixing in Fermi decays Limit for scalar component in beta decays C A /C V 2 <3.6x Bhattacharya et al., PRC77 (2008) p (ev) Absolute branching ratios /SU Very precise T 1/2 determination /ISOLD ft = 1552(12) s for the Fermi decay Isospin Symmetry breaking Correction δ c = 2.0(4) % 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid) 8

9 31 Ar β-2p emitter Nuclear xperimental Decay of IAS through 2p emission Diagonal from decays via single intermediate state from many initial states fed in beta-decay 2p-spectrum 1pspectrum. 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 9

10 Nuclear xperimental Surprise at the neutron drip line: Halo nuclei 1985, First experiments with radioactive nuclear beams, Berkeley (USA) Be, C and Al Tanihata 11 Li 1/2 σ 2 I r mass σ ( p, t) = π [ R ( p) R ( t)] I I + R m ( 11 Li) = 3.30(24) fm R c ( 11 Li) = 2.47(4) fm 6 Li 7 Li 8 Li 9 Li I 2 Why is the mass radius so large? 11 Li Hansen & Jonson urophys. Lett. 4 (1987) 287 nergy threshold effect (S 2n = 378(5)keV) Highlight by nuclear reactions ffects in beta decay 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 10

11 3/2 - I Nuclear xperimental Li T 1/2 = 8 ms Beta decay of an exotic nuclei β ven ven a neutron rich rich --nuclei nuclei emit emit charged particles Li+t Li+d 9 Li 8.82 Jonson Azuma Be+2n α+3n d p nergías (ev) Be Be+n γ 11 Be ½ - ½ + Q = ev, T 1/2 = 8.2 ms b(320) = 6.3(6) % (1s 1/2 ) 2 /(0p 1/2 ) 2 ~1 (1s 1/2 ) 2 /(0p 1/2 ) 2 ~1 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 11

12 Nuclear xperimental Beta-delayed deuterons T. Nilsson Q βd = S 2n ev.j.g. Borge et al., Nucl. Phys. A560 (1993) 664 Anthony et al., PRC 65 (2002) cm Intensity (decay -1 ev -1 ) B.R. Two Orders of agnitude less than expected xploring w.f. 10 fm.v. Zhukov et al., PRC47 (1993) 2937 D. Baye et al., Prog. Th. Phys. 91 (1994) 271 B.R. 2.8(5) x 10-6 F.C. Baker, Phys. Lett. B 322 (1994) 17 First case of β-decay to the continuum Riisager et al., PLB235(90)30 d (kev) 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 12

13 11 Li βd spectrum finally TRIUF!! Nuclear xperimental Implantation of 11Li beam on DSSSD Detector Very precise B.R. Low detection threshold Low beta background DSSSD 16x16 mm 2, 70µm thick History of each decay 48x48 strips, 300 µm, 2304 pixels J. Büscher et al., NI B in press 8 x 10 7 ions implanted in 133 h T 2 T 1 B.R = 1.30(13)x10-4 cm > 200 kev Deuteron Spectrum Decay to the continuum confirmed Raabe et al, PRL 101 (2008) th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 13

14 Nuclear xperimental xotic Radioactivities 1p-radioactivity (Z,N) p + (Z-1,N) These nuclei at the edge of nuclear existence highlight various phenomena related to the binding of nucleons in the nucleus 2p-radioactivity (Z,N) 2p + (Z-2,N) Zn Ni Fe 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 14

15 Nuclear xperimental 1 Proton Radioactivity Proton-radioactivity from gs fixed the proton drip-line of this region. First observed in 151 Lu & 147 Tm GSI) mission of protons only from odd-z [50-83], 28 g.s. proton emitters identified. The sensitivity of T 1/2 to angular momentum allows for the assignment of 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). p-emission from highly deformed nuclei has been observed and decay rates explained assuming Nilsson states. Stringent test of shell model beyond drip line. 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 15

16 Nuclear xperimental Two proton Radiactivity Found 2002 By Bordeaux & Warsaw Predicted in the 60 s by Goldanskii as consecuence of the pairing force easier to eject the pair that break it apart iernik et al, NI A 581 (2007) 194 PRL 99 (2007) PRC 76 (2007) R Two proton correlations needed to learn about nucleon-nucleon correlations! 2p-correlations observed in p-radioactivity Direct emission 43 Cr-p-p 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 16

17 Nuclear xperimental irror Asymmetry? Charge independence hypothesis of nuclear interactions: symmetry of analog β transitions β - : n p + e - + ν n ft - p ± ft = 2 ± 2 gv BF + g A δ + ft = ft 1 β + : p n + e + + ν.c. : p + e - n + ν Isospin symmetry breaking asymmetry in mirror β-decays K B ± GT 2 K g 2 = 6146(6) s A 2 = 1.587(3) g g V V n ft + p δ = δ nuc + δ SCC 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 17

18 Systematics of experimental δ values (A 40) Nuclear xperimental Thomas et al., AIP Conf. Proc 681, p. 235 δ = 4.8 (4) % Allowed Gamow-Teller transitions (log(ft)<6) 17 couples of nuclei 46 mirror transitions A = 9 A = 17 Average asymmetry δ : 11 (1) % in the 1p shell (A<17) 0 (1) % in the (2s,1d) shell (17<A<40) 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 18

19 Nuclear xperimental First identification of a proton-halo state Rolfs, NPA217(73)29 17 Ne 16 F 18 Ne 19 Ne 17 F Beam-on (16) % 1.56(20)%, Ogawa et al., J. Phys. G24 (1998) 143 Beam-off δ = ft + /ft = -0.55(09) δ = ft + /ft = -0.55(09) Borge et al., PLB317(93)25 Asymmetry Halo Structure 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 19

20 Nuclear xperimental A = 9 Isobar Large asymmetries δ = ( ft) ( ft) + 1 δ 3 δ=1.2±0.5 δ 0 Nyman et al., NPA 510 (1990) 189 ikolas et al., PRC 37 (1988) 766 F. Ajzenberg-Selove, NPA 490 (1988) 1 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 20

21 Nuclear xperimental Why to Study Light Nuclei? xact A-body calculations possible for A 12 Green Funtion onte-carlo methods Non-core Shell-model Crucial for bridging A=5 and A=8 gaps in Big Bang and Stellar nuclear synthesis The α(αn,γ) 9 Be + 9 Be(α,n) 12 C Competes with triple-α in n-rich scenarios Importance of the α +n 5 He(α, γ ) 9 Be xperimentally β-decay provides Clean way to feed unbound states Break-up mechanism not fixed by kinematics 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 21

22 Nuclear xperimental 9 B States fed in β-decay of 9 C sum = recoiling + recoiling first first + = 92 kev (9/8) for Be(0 ) 5 x 2 ev (9/5) for Li(3/ 2 ) 8 + = 3.0 ev (9/8) for Be(2 ) 8 + Sequential IAS Decay of 12.2 ev State via 8 Be(gs), 8 Be(2 + ), 5 Li(gs) and 5 Li(1/2) (ev) R-atrix-formalism applied. C-simulations to account for efficiencies of each channel m u s Results : 12.19(4) ev Γ: 450(20) kev p,α,α(kev) J: 5/2 B GT : 1.20(15) UC Bergmann, NPA 692 (2001)427 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 22

23 Nuclear xperimental A = 9 isobar 3/2-5/2 - δ = δ3.4(7) 3 5/ Γ=0.45 (1/2,5/2) - The large asymmetry observed in the β-transitions to the high excited states cannot be due to nuclear structure effects as the gs transitions have equivalent strength, it (1/2) must be - due to different δ=1.2±0.5 coupling to the continuum 3/2-3/2 - δ 0 = 0.032(3) 54.1(15)% Nyman et al., NPA 510 (1990) 189 ikolas et al., PRC 37 (1988) 766 PLB576 (2003)55 F. Ajzenberg-Selove, NPA 490 (1988) 1 NP A692(2001)427 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 23

24 Nuclear xperimental Summary Decay modes: peering into nuclear structure xotics decays: testing shell model beyond the drip line peering into nucleon-nucleon correlations Large Asymmetries: 17 Ne, 17 N halo structure 9 C, 9 Li coupling to the continuum Level densities Fluctuations Chaos Relevant for astrophysics 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 24

25 Nuclear xperimental The future is bright! ISOLD THORY GSI GANIL/SPIRAL With the power of the new accelerators And the developments in detectors We will discover new structures and characterize the inmense amount of new nuclei Thanks for your Attention!! 50th Anniversary Karlsruher NuklidKarte aría José Gª Borge, I,, adrid 25