Nuclear spectroscopy using direct reactions of RI beams

Transcription

1 Nuclear spectroscopy using direct reactions of RI beams Introduction Spectroscopy of exotic nuclei (inv. kin.) Recent experimental results SHARAQ project in RIBF highly excited exotic states spectroscopy of medium-heavy/heavy nuclei Summary CNS, University of Tokyo S. Shimoura

2 Introduction Structure information of nuclei as functions of N and Z Shell Evolution, Structure Change Collectivities (clustering) / Single particle structure in excited states Nuclear responses Disappearance of N=20 magicity Decouple of proton/neutron motion New magic numbers 6, 16 Cluster structure Disappearance of N=8 magicity

3 Inverse Kinematics w/ RI beam ( MeV/u) RI beam ( pps; E~a few %) Exc. States γ rays Decay Fragments Interaction Target as probe ( mg/cm 2 ) Formation of Excited States of Exotic Nuclei Direct reactions and their selectivities In-beam spectroscopy measuring decay products Invariant-mass/γ-ray spectroscopy Particle detectors at forward angles (kin. focus.) Gamma detectors surrounding target (Doppler shift)

4 Invariant Mass Spectroscopy Invariant Mass M inv2 = (Σ E i ) 2 (Σ p i ) 2 E x = M inv M A = E decay + S measuring momentum vectors of particle and/or γ Doppler correction of γ invariant mass of γ and particle S (A-1)+N (A-2)+N 1 +N 2 A

5 Probes for direct reactions ( MeV/u) Heavy Nuclei: Strong Coulomb Field Coulomb Excitation, Coulomb Dissociation E1, E2, (M1) / Isovector H, D, 4 He [Liquid targets] Inelastic Scattering Isovector (H) / Isoscaler(H, D, 4 He) Spin-Flip (H, D) / Spin-Non-Flip (H, D, 4 He) Charge Exchange Fermi type (H) / Gamow-Teller type (H, D) Nucleon Transfer (α,t), (α, 3 He) Reaction Knockout Other (Be, C, ) Inelastic Scattering Knockout / Fragmentation Dirty RI beams and/or Changing Target Same Nucleus can be populated via Different Processes without changing Detector System

6 Observables reaction/decay meas. Yields (Cross Sections) / Lifetime / Width Spectra : As a function of Exc. Energy (+ incident energy) Properties of populated states ( Selectivity) Angular Distribution / Momentum Transfer Reliable Reaction Models with small numbers of parameters Assignment of L J π Eikonal Model [Knockout] Virtual Photon / DWBA / Coupled Channels [Coulex, Inelastic, Transfer] Optical Potential / Transition Density Folding Model with Density Dependent Effective Interaction Angular Correlation / Alignments Assignment of J π Cross sections as a function of

7 Analysis of Alpha inelastic excitation WF s of gnd. and exc. states (φ 0 (r), φ(r)) Gnd. State density (ρ 0 (r)) Distorting pot. (V 0 (r)) O.M. analysis Microscopic Macroscopic BM; Tassie α, β, δ Folding with effective interaction v eff Macroscopic BM β, δ DWBA Transition Matrix Element transition density (ρ tr (r)) Transition pot. (V tr (r)) δ sum rule Elastic Scat. Data Global Systematics Experimental Data Integrated C.S., Ang. Distr. Ang. Cor. J π, δ=βr,

8 Alpha inelastic scattering DWBA by using single folding model with DD interaction Collective form factor Compression mode Tassie model Multipole Decomposition Analysis (MDA)

9 4 He( 12 Be, 12 Be γ) at 60 A MeV γ spectrum coincident with 12 Be ejectiles 2.1 & 2.7 MeV States excited by (α, α ) DWBA [ col. FF & folding pot.] Angular Distributions of 12 Be*

10 4 He( 12 Be, 12 Be γ) at 60 A MeV Angular distribution of γ-decay after (α,α ) 2.1 & 2.7 MeV States excited by (α, α ) Alignments of 12 Be* Anisotropic Angular Distribution of γ Consistent with Prediction of DWBA calculation assuming 2 + & 1 - excitation, resp. Confirmation of 1 - assignment for 2.7 MeV state

11 Alpha inelastic scatterings 4 He( 14 O, A MeV No bound states in 14 O 14 O* 13 N+p, 12 C+2p, 12 C*+2p, 10 C+α, 10 C*+α : Invariant mass Isoscalar E0 & E1 modes (compression) Multipole Decomposition Analysis (MDA) of Isoscalar excitation Effect of Continuum Compression modes

12 4 He( 14 O, 14 O * ) at 60 A MeV 14 O* 13 N+p, 12 C+2p, 12 C*+2p, 10 C+α, 10 C*+α

13 4 He( 14 O, 14 O * ) : Strength distribution Monopole Dipole L=0 L=1 RPA Calc. (Sagawa) RPA Calc. (Sagawa) 14 C 14 O 5 Ex (MeV) 20 5 Ex (MeV) 20 One bound 0 + state in 14 C One bound 1 - state in 14 C

14 Alpha inelastic scatterings (2) 4 He( 12 Be, 6 He A MeV Cluster states in 12 Be Invariant mass L=0, 2, (4) excitations Multipole Decomposition Analysis (MDA) including decaying process

15 4 He( 12 Be, 12 Be * ) Angular Distribution & Angular Correlation Angular distribution of (α,α ) Angular correlation of 6 He+ 6 HeDecay (interference) MDA analysis

16 4 He( 12 Be, 12 Be * ) : Deduced levels (0 +, 2 + ) 100%

17 4 He( 12 Be, 12 Be * -> 6 He+ 6 He) : Deduced levels Several levels: Coupling to 6 He ( * ) + 6 He ( * ) 8 He ( * ) + 4 He channels etc.

18 Nucleon Transfer from A MeV γ spectroscopy of proton single particle states in neutron-rich nuclei 4 He( 12 Be, 13 B*) 4 He( 22 O, 23 F*) p n

19 N-rich N=8 Nuclei Spin-orbit splitting between νp 1/2 & νp 3/2 depend on the number of protons in dp 1/2 orbit attracting νp 1/2 orbit V στ p n n-rich Boron 8 sd p 1/2 p 3/2 p n n-rich Beryllium 13 B Spherical ground state How about excited states? Deformed core + proton? 6 sd p 1/2 p 3/2 12 Be Low-lying 2 + state Low-lying 1 - state Low-lying state Magicity loss in N=8 Deformed ground state Change of Boron Proton Shell as a function of configuration Deformed mean field? sd p 1/2 p 3/2 p n p n 13 B 13 gs B* sd p 1/2 p 3/2 Proton intruder state

20 4 He( 12 Be, A MeV Deformed 12 Be core + 1 proton? C 2 S(BM) ~ 0.27 for δ=0.4 β( 12 Be(p,p )) ~ [101]1/2 Spherical G.S. Deformed Excited 1/2 +? [220]1/2 [101]3/2 ε 2 ~ δ ~ 0.95β 0.3 [110]1/2

21 Spectra of 14 C, 12 Be, 11 B, and 13 B S n = C 11 B 13 B Be

22 4 He( 12 Be, A MeV 3.71 & 4.83 MeV states strongly excited by (α, t) Different transferred L GRAPE NaI(Tl) array 12 Be beam Liq. He target [kev] 4 He( 12 Be, 13 Bγ)X 11 B(t,p) 13 B 9 Be( 14 B, 13 B) 14 Be(βn) 16 O( 14 N, 17 F) 13 B 12 C( 14 C, 13 N) 13 B 12 C( 13 C, 12 N) 13 B 12 C( 15 N, 14 O) 13 B (13) (18) (16) (12) (13)

23 4 He( 12 Be, A MeV Angular Distribution of 13 B coin. with 4829 kev γ FR-DWBA (DWUCK5) Optical Potential: 12 C + 4 He (entrance) 12 C + 3 He (exit) L=0 -> J π = 1/2 + C 2 S = dep. on Potentials -> Proton single particle state on 12 Be

24 4 He( 12 Be, A MeV Proton single particle state on 12 Be 1/2+ : /2+ : 0.003?? 1/2+ : 0.03? 1/2- : /2- : /2+ 5/2+ 1/2+ : 0.01 PSDFU PSDFU 3/2- Shell model (3hw)

25 1/2 + state in 13 B* by AMD Kanada-Enyo prelim. 1/2 + 1 :Deformed 70% ν1 hω 30% π1hω+ν2hω Proton excitation Deformed ground state in 12 Be 1/2 + 2 :Spherical π1hω+ν0hω

26 Summary Alpha induced direct Reactions combined with invariant-mass/γ spectroscopy are powerful tools to investigate excited states in exotic nuclei Isoscalar monopole and dipole response Cluster states Nucleon transfer reactions at A MeV are useful for searching single-particle states Structure change in excited state Single particle structure

27 SHARAQ Spectroscopy with High-resolution Analyzer & RadioActive Quantum beams Response of Nuclear System using Intermediate-Energy direct reactions ( A MeV) Studies using New Quantum Probe-RI beam- Large Isospin and Mass Excess Various I π Controlling Transferred Momenta, Q-values, Spin, Isospin S, T,q-ω Accessing kinematical area/conditions inaccessible by stable nuclear beam Ordinary kinematics -> High Resolution Spectrometer + High Quality RI Beam + (Detectors of decaying particles) Asymmetric nuclear System studied using stable probes Inverse kinematics + Invariant Mass / γ-decay / Recoil and High-resolution missing-mass spectroscopy

28 SHARAQ RI Beam (E = MeV/A) as a new PROBE beam (stable) 寫楽 Spectroscopy with Highresolution Analyzer & RadioActive Quantum beams to nuclear systems Large Isospin iso-tensor excitations Large internal energy (q,ω) inaccessible by stable beams beam (unstable) (q,ω) ejectile (unstable) large negative Q-value Endothermic (q,ω) ejectile (stable) small Q-value ω IVSMR Multi n s DGT GT SHARAQ Photon line: q=ω Stable Beam Exothermic Charge Exchange Reactions q

29 Multi-neutron system 3,4 n ; 6,7 H with small q Resonant states? B C He LiBe H n Correlation in multi-body scattering states? Correlation Spectral shape Superheavy Multi- Hydrogen Neutron ω (MeV) He 4 He 4n 4He -> 4n 4 He( 8 He, A MeV 4n Threshold q (MeV/c ) 8 Be 4 He( 18 O, A MeV

30 Multi-neutron system 2 n 3,4 He( 8 He, 8 Be) 3,4 n p 6,7 Li( 8 He, 8 Be) 6,7 H 4 n Double Dipole s α p n 2 n 2 n p s p 7 Li p Dipole x Fermi/GT s n p 7 H n

31 SHARAQ Spectrometer Configuration QQDQD Parameter Momentum resolution p/p ~ 1/15000 δe x ~300 kev for A=10, E=250MeV/A Maximum rigidity Bρ = 6.8Tm Solid angle Ω =2-5 msr Momentum acceptance +/- 1 % Rotatable High-quality RI beam-line Dispersion measuring/matching

32 SHARAQ Spectrometer QQDQD Recycled magnets from SMART newly constructed Super-conducting quadrupole doublet

33 Specification dispersion (D) 5.8 m horizontal magnification (M x ) 0.42 D/M x 13.7 m momentum resolution (image size 1mm) 1/13700 vertical magnification (M y ) 0.3 angular resolution < 1 mrad vertical acceptance ± 1.7deg for spot size 60mm 10mm (in dispersion matching operation) horizontal acceptance ± 1deg solid angle 2 msr for spot size of 10mm 10mm solid angle 4.8 msr

34 Current Plan of installation site Beamline with large dispersion Event-by-event measurement Dispersion matching Same resolution as the SHARAQ spectrometer

35 Possible researches using SHARAQ spectrometer Elastic scattering of exotic nuclei Optical potential (OP) : Systematics in Radii (Isospin dependence) Input for reaction calculation such as Reaction cross section from OP LS pot. by pol. p target RI Target (probe) SHARAQ RI Inelastic scattering / Charge exchange of exotic nuclei Direct relation to beta decay (p,n), (d,2n), (d,2p) [low Ex] Highly excited states [combination of γ array] q ~ 70 MeV/c & Ex ~ 3 MeV for A=100, T/A=250 γ array for better Ex / cascade γ-decay Missing mass spectroscopy for direct γ-decay : (p,p γ) Measurement of recoil (proton, neutron, deuteron, ) Nuclear responses / Pigmy resonances RI γ Target (probe) SHARAQ RI

36 Thank you for attention Open for everyone interested in SHARAQ to SHARAQ Collaboration