Nuclear spectroscopy using direct reactions of RI beams

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

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

Inverse Kinematics w/ RI beam (30-400 MeV/u) RI beam (0.1 10 5 pps; E~a few %) Exc. States γ rays Decay Fragments Interaction Target as probe (50 300 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)

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

Probes for direct reactions (30-100 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

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

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,

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

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* 2 + 1 -

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

Alpha inelastic scatterings 4 He( 14 O, 14 O*) @ 60 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

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

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

Alpha inelastic scatterings (2) 4 He( 12 Be, 6 He+ 6 He) @ 60 A MeV Cluster states in 12 Be Invariant mass L=0, 2, (4) excitations Multipole Decomposition Analysis (MDA) including decaying process

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

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

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.

Nucleon Transfer from 4 He @ 30-50 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

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 0 + 2 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

4 He( 12 Be, 13 Bγ) @ 50 A MeV Deformed 12 Be core + 1 proton? C 2 S(BM) ~ 0.27 for δ=0.4 β( 12 Be(p,p )) ~ 0.6-0.7 8 [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

Spectra of 14 C, 12 Be, 11 B, and 13 B 2 + 0 + 1-7012 6589 6094 S n =4878 + 1-2700 0 + 2240 2 + 2100 0 + 14 C 11 B 13 B 0 + 12 Be

4 He( 12 Be, 13 Bγ) @ 50 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 4829 1.00 0.03 1.00 0.34 4131 0.59(13) 1.00 0.40 0.23 0.78 0.39 3713 0.95(18) 0.25 1.00 1.00 1.00 3681 0.48(16) 0.38 1.00 3534 0.31(12) 0.19 1.00 3482 0.06(13) 0.06 0.60

4 He( 12 Be, 13 Bγ) @ 50 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 = 0.1 0.2 dep. on Potentials -> Proton single particle state on 12 Be

4 He( 12 Be, 13 Bγ) @ 50 A MeV Proton single particle state on 12 Be 1/2+ : 0.30 1/2+ : 0.003?? 1/2+ : 0.03? 1/2- : 0.87 3/2- : 0.15 3/2+ 5/2+ 1/2+ : 0.01 PSDFU PSDFU 3/2- Shell model (3hw)

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

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 30-50 A MeV are useful for searching single-particle states Structure change in excited state Single particle structure

SHARAQ Spectroscopy with High-resolution Analyzer & RadioActive Quantum beams Response of Nuclear System using Intermediate-Energy direct reactions (150-400 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

SHARAQ RI Beam (E = 150-400 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

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) 45 40 35 30 8 He 4 He 4n 4He -> 4n 4 He( 8 He, 8 Be) @ 200 A MeV 4n Threshold 0 50 100 150 200 q (MeV/c ) 8 Be 4 He( 18 O, 18 Ne) @ 40 A MeV

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

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

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

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

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

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

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