Nuclear Physics using RadioIsotope Beams T. Kobayashi (Tohoku Univ.)
Nucleus: two kinds of Fermions: proton & neutron size ~1fm strong interaction: ~known tightly bound system < several fm < 300 nucleons Sn stable Pb known unknown Nuclear Chart proton# Elements He O Ca Ni Electromagnetic excitation Internal motion single-particle properties neutron# from several experiments we were involved Magic Numbers exotics 2,8,20,28,50,82... Beyond the Drip Line bulk properties Radius (size) R T astrophysics Nucleosynthesis γ Other Topics
tool making of RI beams
[1] Making of RI (Radio Isotope) Beam Energy : few tens - several hundreds MeV/nucleon Projectile Fagmentation H B nucleons V b F nucleons He Li Be B C N O 100mb V f Target 1mb primary heavy-ion beam projectile fragments secondary beam line target Accelerator Facilities (Bevalac @LBL : < 2 GeV/A) Ring Cyclotron @RIKEN : < 135 MeV/A HIMAC Synchrotron @NIRS : < 0.4 GeV/A SIS18 Synchrotron @GSI : < 2 GeV/A selected RI beam Reaction cross section Scattering Fragmentation... 1984~
bulk property Nuclear Radius
[2] Nuclear Size (Radius) : as bulk property Method : Interaction cross section σ I : RI beam σ I (B+T)π(R B +R T ) 2 target matter radius α (Rutherford) proton scattering electron collinear laser spectroscopy "charge radius" Measurement : attenuation target N in N out N out N in = exp( N T σ I ) σ tot [mb] 500 100 50 p-p nucleon-nucleon cross section p-n Energy pri. tar get MUSIC TOF scintillat or MWPC TOF 10 50 100 500 1000 Energy [MeV] ~1 GeV/nucleon MWPC target only at SIS18 @GSI
Interaction Cross Section σ I Root Mean Square Radius R rms r 2 σ I [mb] 120 isotopes / ~20years σ I = π [ R I ( 12 C) + r 0 A ] 1/3 2 R I ( 12 C) = 2.61 fm,r 0 = 1.14 fm Mass Number A R rms [fm] r 0 A 1/3 Mass Number A Glauber (Multiple Scattering) model measurements @ Bevatron (LBL) @ SIS18 (GSI) Density distribution ρ(r) : target: known projectile: Woods Saxon, Harmonic, Gauss Nucleon-nucleon cross section:
R rms - r 0 A 1/3 +0.5 fm -0.2 fm He Z H N Proton-Rich side C B Be Li O N Si Al Mg Na Ne F 6 He 8 He 11 Be 11 Li S P 14 Be by adding neutrons ρ(r) Ar Cl 19 C 17 B 19 B 23 O 24 O 22 N 23 N Neutron-Rich side Large / extended nuclei near the drip lines +xn ρ(r)? ρ(r)? for stable nuclei : 48 Ca(Z=20, N=28), 208 Pb(Z=82, N=126) : r n -r p < 0.1 fm r r r
Neutron Halo Density ρ(r) [fm -3 ] 10-0 10-1 10-2 10-3 10-4 11Li Density Distribution 10-5 0 10 r [fm] low density tail 11,14Be, 11 Li, 15,17 B, 19C, 22 N, 23O, 24 F small separation energy S n, S 2n < 1 MeV mostly neutron 2s 1/2 orbit L=0, no centrifugal barrier
Neutron/Proton Skin 10 0 6He Density Distribution Isotope Shift (R proton ) Interaction cross section (R matter ) R neutron Density ρ(r) [fm -3 ] 10-1 10-2 R rms ( 6 He) = 0.870.06 fm proton Neutron Na Ar 10-3 0 r [fm] bulk excess (high-density tail) 5 R n - R p [fm] R n > R p R p > R n Mass Number
ρ(r) +xn ρ(r) ρ(r)? r r r for unstable nuclei with Fermi-energy difference R p -R n [fm] 0.6 0.4 0.2 0-0.2 32 33 21 20 34 Neutron skin -0.4 35 21 23 38 37 25 39 40 27 26 Ar Na Proton skin 29 28 30 31 E F U proton neutron r -0.6-20 -10 0 10 20 E F =S p -S n [MeV]
internal motion Single particle properties: via momentum distribution p target
σ I R rms one information on bulk property Next: How nucleons are moving inside the nucleus? single-particle property (1) momentum distribution of nucleons ρ (q) = d σ d r = φ q p φ( q r )= ψ( r ) e i r r ( ) 2 q d v r ρ(r) = ψ(r) 2 wave function in momentum space How? knockout φ r q density distribution of nucleons ( ) Fourier wave function ψ( r ) transform in real space atomic physics : e(e,2e) nuclear physics: A(e,e'N), A(p,pN) Inverse kinematics S N: separation energy q : momentum L : angular momentum p target
Shell model: one-particle orbit 1f,2p 1d,2s 1p 1s harmonic Magic Numbers 28 20 8 2 1f 5/2 1f 7/2 2s 1/2 1d 3/2 1d 5/2 1p 1/2 1p 3/2 1s +ls 1/2 +Spin Orbit s,p,d 2s,1p 1s Coulomb (long range)
Neutron knockout from neutron-halo/skin nuclei knockout weakly bound valence neutron p( 6 He,pn) 5 He S 2n ( 6 He)~1MeV 60 11 Li p1/2 p n p( 11 Li,pn) 10 Li p 3/2 s 1/2 S 2n ( 11 Li)=0.3MeV rms momentum width [MeV] 40 20 11 Li 2s1/2 6 He p3/2 11 Li p3/2 0 4 8 2s 1/2 Separation Energy S n [MeV] p 1/2 p 3/2 + 0 p s 1/2 n n @85 MeV/A 5He & 10 Li are unbound resonances
Neutron Halo, ν2s 1/2 orbit, magic numbers Shell model: one-particle orbit 20 Mg 21 Mg 22 Mg 23 Mg 24 Mg 25 Mg 26 Mg 27 Mg 28 Mg 29 Mg 30 Mg 31 Mg 32 Mg 33 Mg 20 Na 21 Na 22 Na 23 Na 24 Na 25 Na 26 Na 27 Na 28 Na 29 Na 30 Na 31 Na 32 Na 1f,2p Magic Numbers 17 Ne 18 Ne 19 Ne 20 Ne 21 Ne 22 Ne 23 Ne 24 Ne 25 Ne 26 Ne 27 Ne 28 Ne 29 Ne 30 Ne 16 F 17 F 18 F 19 F 20 F 21 F 22 F 23 F 24 F 25 F 26 F 27 F 29 F 31 Ne 1d,2s 28 20 1f 5/2 1f 7/2 2s 1/2 1d 3/2 1d 5/2 s,p,d Z=8 13 O 14 O 15 O 16 O 17 O 18 O 19 O 20 O 21 O 22 O 23 O 24 O 12 N 13 N 14 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 N 9 C 10 C 11 C 12 C 13 C 14 C 15 C 16 C 17 C 18 C 19 C 20 C 22 C 8 10 B B 11 B 12 B 13 B 14 B 15 17 19 B B B 7 9 Be 10 Be 11 Be 12 14 Be Be Be (N=16) N=20 1p 1s harmonic 8 2 1p 1/2 1p 3/2 1s +ls 1/2 +Spin Orbit 2s,1p 1s Coulomb (long range) Z=2 6 Li 7 Li 8 Li 9 Li 3 He 4 He 6 He 8 He 1 H 2 H 3 H 1 n 11 Li N=8 N=2 large ν2s 1/2 component large (ν2s 1/2 ) 2 component Soft nucleus, extended nucleus Softning(disapperance) of magic numbers & apperance of new magic numbers
internal motion Single particle properties: via electromagnetic breakup B B* γ F N highz
Next: How nucleons are moving inside the nucleus? #2 single-particle property (2) Electromagnetic (Coulomb) Breakup B b highz B σ γ B* N γ (E γ ) F N virtual photon 10 +3 10 +2 N γ (E γ ) σ EMD (B F + N ) = highz N γ (E γ )σ (γ,n)de γ #Photons [MeV -1 ] 10 +1 10 0 1GeV/A 10GeV/A 0.1GeV/A +Invariant-mass method ( P r 1,E 1 ) ( P r 2, E 2 ) Excitation energy of intermediate state (relative energy) M rel M rel = ( E 1 + E 2 ) 2 + ( r p 1 + r p 2 ) 2 m 1 m 2 10-1 0 100 10MeV Eγ [MeV]
Neutron Halo Nuclei with single valence neuron by T. Nakamura et al. (1) 11 Be+Pb 10 Be+n @72MeV/A n (2) 19 C+Pb 18 C+n @67MeV/A n 18 C 10 Be 1/2 - ν2s 1/2 + 1/2 11 Be 10 Be+n S n =E s =0.5MeV dσ CD de rel = N E1 (E x ) db(e1) de rel E rel = 0.6E s S n = 0.16±0.11 MeV? 0.5MeV J π = 1/2 +, 5/2 +? h 1 E s 2 1/2 + ν2s 1/2 S E s E rel db(e1) e i r q rr e Z de x A ry 1 e κr m r S factor ~ 0.9 2 E s ( E x E s ) 3/2 4 E x consistency with other measurements? σ I ( 19 C), dσ/dp( 19 C 18 C)
Exotics beyond the drip line small neutron star?
Exotic Resonances beyond the Drip Line Z=8 12 N 13 N 14 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 N 9 C 10 C 11 C 12 C 13 C 14 C 15 C 16 C 17 C 18 C 19 C 20 C 21C 22 C 8 10 B B 11 B 12 B 13 B 14 B 15 17 19 B 16B B 18B B n 7 Be 13Be 9 Be 10 Be 11 12 Be Be 14 Be 11Li 10He 8He Z=2 6 Li 7 Li 8 Li 9 Li 3 He 4 He 6 He 8 He 10Li 11 Li 5He 7He 9He10He 10He : target p n 1 H 2 H 3 H 1 n N=2 4H 5H 7H N=8 double magic N/Z=4 150 A. Korsheninnikov et al. 11Li+CD28He+n+n+x @61MeV/A 100 Counts [arb.] 50 E= 1.20.3 MeV Γ< 1.2 MeV later: 6,8 He(p, 2 He) 5,7 H 0-2 0 2 4 6 E rel (8He+n+n)
Nuclear Astrophysics Nucleosynthesis in stars & super nova
Nucleosynthesis in stars : up to Fe/Ni = fusion reactions at extremely low energy : T= 10 7 ~10 9 K E= 1~100 kev U 0 E c few MeV R E in few kev r Nucleus Hydrogen burning process : p(p,e + ν)d(p,γ) 3 He 14% 3He( 3 He,2p)α 3He(α,γ) 7 Be 7Be(e - ν,γ) 7 Li(p,α)α 0.015% 7 Be(p,γ) 8 B(e + ν)2α 8 B neutrino (p,γ) radiative capture reaction involving unstable nuclei ±20% 7Be(p,γ) 8 B T 1/2 ( 7 Be)=53day T 1/2 ( 8 B) =0.8sec many other (p,γ) reactions upto Fe/Ni conventional method: proton(~fewx10kev) + radioactive 7 Be target small cross sections (~10nb) target thickness...
Electromagnetic breakup reaction γ+ca+b using virtual photon γ inverse reaction radiative capture reaction : a+bc+γ 8B γ 8B* Pb 7Be p detailed balance σ(γ + c a + b) = (2 j a + 1)(2 j b + 1) 2(2 j c +1) k k γ 2 σ (a + b γ + c) ~10 3 +target thickness + kinematic focus >10 6 8B+Pb 7 Be+p N. Iwasa et al. T.Motobayashi et al. 8B(γ,p) 7 Be @47,52,254 MeV/A S(E) σ (E)E exp b E @254MeV/A
Nucleosynthesis towards heavy elements: in Super Nova Nuclear Chart again Z=82 known r process unknown Z=50 stable? N=126 What happened many times. Z=20 Z=28 Z=8 Z=2 N=8 N=2 N=20 N=28 N=50... N=82 through unknown isotopes mass, separation energy, life time,... needed, of cource We know magic number is not stable towards drip line in the light-mass region. heavy-mass region?
Nuclear Physics using RI Beams Experience in past 15-10 years seems to show (1) Extrapolation of the knowledge near the stability line drip (far from the stability) lines failed in most cases. (2) Going toward the drip lines almost always gave surprize even in the light-mass region maybe a problem in theory? predictability? no "standard model" New Facilities are being built to extend our knowledge toward the drip lines in the heavy-mass region facilities: GSI upgrade (Germany), RIA (USA), RIBF (Japan) RI Beam Technique was initiated by Japanese group (in USA) (please let us keep the intiative)