Electron Scattering for Neutron-Rich Nuclei

Transcription

1 Electron Scattering for Neutron-Rich Nuclei Toshimi Suda for SCRIT collaboration Tohoku University, Sendai, JAPAN

2 Recent publications in 2017 A review paper : Progress of Particle and Nuclear Physics 96 (2017) First physics paper from SCRIT : Phys.Rev.Lett. 118 (2017)

3 World s first electron scattering for short-lived unstable nuclei

4 Electron Scattering Electron scattering is the most powerful tool to study the internal structure of atomic nuclei ~e ~e 0 1. point particle 2. electromagnetic interaction i) well-understood ii) coupling : charge and current => el.mag. structure iii) weak -> probing whole volume perturbation theory iv) exp. data => structure information 3. variable q for fixed ω! = e e 0 ~q = ~e ~e 0 Electron scattering provides direct and unambiguous structure information of atomic nuclei essential inputs for nuclear structure theories for hardon-induced scattering data

5 proton number Nuclei studied by electron scattering strictly limited to stable nuclei never applied for exotic nuclei (short-lived) 208Pb H.deVries, C. dejager and C. devries Atomic Data and Nuclear Data Tables 36 (987) ,48Ca 50 16O Most of stable nuclei (except noble gases such as Kr, Xe) some example for unstable nuclei such as 3 H, 14 C, 41 Ca etc... neutron number

6 Electron scattering for stable nuclei charge distribution valence neutron 17O deformation theory 154 Gd Φ(p) 2, S-factor quasi-elastic scattering d 6 dk e 0d e 0dp p d p = K d ep d S(E m,~p m ) exp. 16O(e,e p) p 3/2 p1/2

7 s-factor by elastic e-scattering Experimental determination of 3s1/2 in Pb 206Pb, 205 Tl (e,e ) 3S1/2 (r) 2 = Pb (r) Tl (r) = = X82 i=1 Z X81 (r) 2 i=1 (r) 2 e i~q ~r ( F Pb (q) 2 F Tl (q) 2 )d 3 q Po Bi ~0.6 Pb Z = 82 Tl Hg Au N = 126 J.M. Cavedon et al. Phys. Rev. Lett. 49 (1982) 978.

8 Nuclear responses to (ω, q) ~e ~e 0! = e e 0 d 2 d!d ~q = ~e ~e 0 elastic time-like region ω q inelastic Giant Resonances Quasi-elastic space-like region real photon Δ, N*.. ω = q

9 electron scattering for exotic nuclei Targeting production-hard short-lived exotic nuclei R. Hofstadter 1961 Nobel Prize Ways to realize electron scattering off exotic nuclei 1) fixed target 2) ea collider 3) electron at rest e A e A e A Ee ~ 300 MeV Ee ~ 300 MeV EA ~ 600 GeV/A (γa ~ 600) My talk ELISe@FAIR

10 e-scatt. off short-lived exotic nuclei expected low luminosity elastic scattering (largest σ) Hofstadter s experiments for exotic nuclei Elastic Scattering for spin-less nuclei PWIA d d = d Mott d F c(q) 2, d Mott d = z2 2 4e 2 F c (q) = cos 2 sin 4. c( r)e i q r d r c (~r) = X p p(~r) p (~r) charge density distribution

11 Beyond the charge radii <r 2 c >= Z r 2 c (r) d~r optical isotope shift <r 2 > 1/2 = fm x ChargeDis_132Sn_fixR2_2 FF_132Sn_fixedR2 UNI Uni 2PF2 <r 2 > 1/2 = fm Gauss 2PF gauss D a) 2PF b) ρ (r) (fm -3 ) ρc(fm -3 ) <r 2 > 1/2 =4.709 fm Fc(q) 2 F(q) r (fm) r (fm) Momentum Transfer (MeV/c) q (MeV/c) 10-4

12 Accessible q-range for L and Z 0.6 q max /q 2nd dip First generation exp. / Z 2 / 1/q 4 L ~ /cm 2 /s T. Suda and H. Simon Prog. Part. Nucl. Phys. (accepted)

13 SCRIT Facility as of today

14 SCRIT electron scattering RIBF World s first electron facility dedicated for exotic nuclei RIKEN RI Beam Factory (Japan)

15 World s first electron scattering facility for exotic nuclei SCRIT Electron Scattering Facility ( Self-Confining RI Target ) RTM : Race Track Microtron injector + ISOL driver 150MeV/0.5 ma peak/2 μs pulse Electron energy MeV stored current 300 ma (as of today) beam life time 2 hours Luminosity Monitor ISOL (ERIS) photofission of 238 U ~ 10 8 fission/w ISOL + electron accelerators Electron Spectrometer Δp/p ~ 10-3 ΔΩ ~ 100 msr long target acceptance ~ 50 cm

16 what is SCRIT Self-Confining RI Target)?? Idea Problematic ion trapping electron storage ring new ion trap for e-ri scattering trapping RIs on electron beam automatic e-scattering off trapped RIs) ionized residual gases are trapped by the circulating electron beam e-ring vacuum chamber scattered electron RIs from an external ion source electron beam trapped RI electron residual gas ions ill problem of e-storage ring e-beam electrode electrode manipulating injection,trapping and ejection for short-lived RI Nucl. Instrum. Methods A532 (2004) 216. Phys. Rev. Lett. 100 (2008) Pays. Rev. Lett. 102 (2009)

17 Luminosities ~10 7 ions are trapped on e-beam (~ 1 mm 2 ) N t ~10 7 /mm 2 => 10 9 /cm 2 Ee Nbeam ρ t L Hofstadter s era (1950s) 150 MeV ~ 1nA (~10 9 /s) ~10 19 /cm 2 ~10 28 /cm 2 /s JLAB 6 GeV ~100μA (~10 14 /s) ~10 22 /cm2 ~10 36 /cm 2 /s SCRIT MeV ~200 ma (~10 18 /s) ~ 10 9 /cm 2 ~10 27 /cm 2 /s

18 First physics run (Stable) 132 Xe(e,e ) Ntrapped ~ 10 Ie = 250 ma => L ~ /cm 2 /s a week measurement Ee = 150, 200 and 300 MeV θ = deg. => q = MeV Ee = 300 MeV Ee = 200 MeV Ee = 150 MeV

19 Using only Ntrapped ~ 10 8 <r 2 > 1/2 = by μ-atom X-rays 132Xe(e,e) DWBA (DREPHA) calculation assuming 2PF distribution

20 First-round experiments Z = 50 N = 82

21 1g7/2 (r) 2 = 133 Sb(r) 132 Sn(r) = = 51X i=1 Z (r) 2 50X i=1 e i~q ~r ( F Sb (q) 2 (r) 2 F Sn (q) 2 )d 3 q Z = 50 N = 82

22 Beyond elastic (charge) scattering elastic inelastic quasi-elastic charge density distribution (deformation, neutron orbit) transition density momentum density distribution, S- factor... towards higher luminosity with limited number of target exotic nuclei

23 Additional Research Opportunity Photonuclear reaction of exotic nuclei at the SCRIT electron scattering facility

24 excitation energy σtot in GDR region Prolate ground state elastic scattering Total Photo-absorption Cross Section (mb) spherical Eγ (MeV) B. L. Berman and S. C. Fultz, Rev. of Mod. Phys. 47 (1975) 713

25 Total Photoabsorption Cross Section 1) Response functions operators : well-known) 2) Sum Rules TRK sum rule Bremmstrahlung sum rule Z 1 0 Z 1 0 (E )de = 2 2 e 2 ~ M = 60 NZ A (E ) E de = 4 2 e 2 3~ NZ A (1 + apple)m (1 + apple) NZ A 1 <r2 > Migdal sum rule Z 1 0 (E ) E 2 de = 2 2 ~ P P : polarizability

26 photonuclear reaction for exotic nuclei so far only way : Coulomb excitation in heavy ion reaction RI beams 1 γ ex. Pb SCRIT facility e-beam E e=ee-eγ Ee γ RI SCRIT purely EM probe well under control negligible multi-stop ultra-forward electron scattering d 2 de e d = X d 2 Ne EL Virtual Photon flux (E,E, ) de d EL (E )

27 Upgrade of the SCRIT facility Injector Microtron Electron beam injection line Electron Ring ERIS (ISOL) Ion beam transport line Veto (γ calorimeters) Forward Electron Detector Neutron Detectors (optional) SCRIT device WiSES

28 Expected reaction rate for L = /cm 2 /s virtual photon theory Z dn de = L d d2 Ne E1 (E,E, ) de d E1 (E ) L = L /cm 2 /s 2 /s 120Sn (stable) 1 day P. Durgapal and D.S. Onley Comp. Phys. Comm. 32 (1984) 291

29 Announcement ECT* workshop July 16-20, 2018 Probing exotic structure of short-lived nuclei by electron scattering Organizers : T. Suda (Tohoku), H. Simon (GSI), T. Otsuka (RIKEN/Tokyo), C. Barbieri (Surry)

30 Summary e-scattering off exotic SCRIT (RIKEN) SCRIT electron scattering facility started its operation. world s first ( and only ) electron scattering facility for short-lived nuclei Final commissioning experiment for stable 132 Xe (e,e ) completed: L ~ /cm 2 /s with ~10 8 ions on e-beam q 1.5 fm -1 first e+ri ( 138 Xe, 132 Sn) scattering starts L > /cm 2 /s : this summer ISOL (γ+u) : towards higher beam power ( 20 W ---> 1 kw) : ~10 11 fission/s 4. Future perspectives Total photoabsorption cross section of exotic nuclei covering the whole GDR region