Reaction Dynamics for Light Dripline Nuclei

Transcription

1 Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) Angela Bonaccorso INFN Sezione di Pisa Advances in Radioactive Isotope Science(ARIS2014) Tokyo, Japan, June 1th- 6th, 2014 Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

2 Ouverture Entering the world of exotic nuclei: probing the unbound by walking at the drip line. Is there a life beyond the dripline? How can we discover it without getting lost? Extend our understanding of the residual nuclear force. Check the limits of validity of structure models such as the SHELL MODEL or ab initio models. Challenges in breakup reaction theory. Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

3 Dynamics of light exotic nuclei Breakup Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

4 Formalism Here we go... A consistent formalism for all breakup reaction mechanisms The core-target movement is treated in a semiclassical way, but neutron-target and/or neutron-core with a full QM method. AB and DM Brink, PRC38, 1776 (1988), PRC43, 299 (1991), PRC44, 1559 (1991). Early eikonal model: I. Tanihata, Prog. Part. Nucl. Phys. 35, 505 (1995), halo-core decoupling. dσ dξ = C 2 S 0 dp n (b c ) db c P ct (b c ), dξ C 2 SCi 2 ξ ε f, k z, P // also ANC = Use of the simple parametrization P ct (b c ) = S ct 2 = e ( ln 2exp[(Rs bc)/a]), R s r s (A 1/3 p + A 1/3 t ) r s 1.4fm strong absorption radius Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

5 Formalism TC Transfer to the continuum: from resonances to knockout reactions First order time dependent perturbation theory amplitude: A fi = 1 i dt < φ f (r) V (r) φ i (r R(t)) > e i(ωt mvz/ ) (1) ω = ε i ε f mv 2 R(t) = b c + vt φ f see ( ) dp n (b c ) = 1 m 1 dε f 8π 3 2 k f 2l i + 1 Σ m i A fi 2 4π Σ jf (2j f + 1)( 1 S jf S jf 2 )F, 2k 2 f F = (1 + F lf,l i,j f,j i )B lf,l i B lf,l i = 1 [ ] kf 4π mv 2 C i 2 e 2ηbc M lf l 2ηb i c Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

6 Formalism TC Final continuum wave functions ( ) Final continuum state: φ lf (r) = C f k i 2 (h(+) l f (kr) S lf h ( ) l f (kr))y lf,m f (Ω f ), S lf (ε f ) is an optical model (n-core in fragmentation reactions, n-target in knockout reactions) S-matrix. Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

7 Examples 13 Be puzzle 13 Be puzzle or of the elusive 1/2+ state in Be isotopes Our level sequence 2s1/2 a_s=- 0.8fm 1p1/2 1d5/2 G. Blanchon et al. PRC82, NPA A 784 (2007) 49 Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

8 Examples n-target optical potential: AB, F. Carstoiu, PRC61, (2000) n- 9 Be optical potential: A.B & R.J. Charity, PRC89, (2014), data from ( ) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

9 Examples Incident energy dependence Resonances, trojan horse knockout 3 2 data p reaction data n reaction data total data elastic react eik elastic eik tot eik σ(barn) E_lab(MeV) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

10 Examples Incident energy dependence Transfer to 10 Be resonances: missing mass experiment. Paper in preparation Diana Carbone, AB, Mariangela Bondì, F. Cappuzzello, M Cavallaro et al. MAGNEX Collabora>on: 1n and 2n transfer experimental campaign d /de x (mb/mev) g.s. (0 + ) g.s.* 3.37 (2 + ) 3.37* 5.96 (2 + ) (2 - ) 7.37 (3 - ) (2 + ) 7.37* * 9 Be( 18 O, 17 O) MeV 3 < lab < (4 - ) (2 + ) 9.27* + 9.4* 9 Be(n,nn) 8 Be 9 Be(n, ) 6 He 1n break-up calculation 16 O has a degenerate gs (1d5/2,2s1/2) 17 O has 5/2+ gs and 1/2+ first excited state at E*=0.87MeV Posi>on and widths of p1/2 and d5/2 resonances in 10 Be perfectly reproduced S n S S 2n E x (MeV) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

11 Examples Kinematics Kinematics From Eq.1 by the change of variables dtdxdydz dxdydzdz e i(ωt mvz/ ) e ik 1z e ik 2z neutron energies to neutron parallel momenta with respect to core to target k 1 = ε f ε i 1 2 mv 2 ; v k 2 = ε f ε i mv 2 ; v to core parallel momentum P // = Er 2 Mr 2 = = breakup threshold at ε f = 0 ++ (T r + M r ) 2 M 2 r (T p + ε i ε f ) 2 + 2M r (T p + ε i ε f ), (2) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

12 Kinematical effects Asymmetric spectra Example deformation effects due to n-target interaction and kinematical cut-off. F. Flavigny, A. Obertelli, AB et al., PRL 108, (2012). Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

13 Kinematical effects Asymmetric spectra Asymmetries at high incident energy Data courtesy of A. Gade Calcula3ons G. Salvioni MSc Thesis in prepara3on. 28S (- 1n) 80.7 d5/2+d3/2 28S (- 1p) s1/2+d3/2 A.MeV 24Si(- 1p) d5/ A.MeV 34Ar (- 1n) s1/2 gs 70 A.MeV 34Ar (- 1n) d3/2+d5/2 Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

14 Kinematical effects Phase space effect Origin of kinematical cut-off (phase space) and deformation effects PRC60(1999) ,PRC44(1991) 1559,AB and GF Bertsch, PRC63(2001) , F. Flavigny, A. Obertelli, AB et al., PRL 108, (2012). (+) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

15 Connecting reaction with structure. Ex: reduction of spectr. fact. Removal of a deeply bound n/p while the weakly bound p/n is un-touched b c Knock out from a deeply bound state x.. 14 O Core. T before T. 13 O. v z. z a0er Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

16 Connecting reaction with structure. Ex: reduction of spectr. fact. S = S n S p 10 20MeV reaction Sn Sp E (m) inc σ exp [MeV] [MeV] [A.MeV] [mb] 9 C 8 C Ca 35 Ca O 12 O Cl 32 Cl Ar 31 Ar S 27 S Si 23 Si C 9 C Li 5 Li O 13 O Ar 33 Ar Be 6 Be Ni 56 Ni S 31 S Ar 45 Ar Si 33 Si Be 9 Be C 14 C 16 C 15 C σ = C 2 S 0 db cp n(b c)(1 P p(b c))p ct(b c) e P p 1 P p(b c) DPP from phase shift, AB, F. Carstoiu, NPA706, (2002) -typically 10% reduction in the cross sections. Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

17 Connecting reaction with structure. Ex: reduction of spectr. fact. S = S n S p 10 20MeV Absolute cross sections Ratios σ = dξ dσ dξ σ exp /σ Theo have been used to validate spectroscopic factors C 2 S (=2j+1, in the IPM ) for single particle orbitals from shell model or ab initio calculations, when available. This is similar to what has traditionally been done for transfer. However in transfer the core-target interaction is treated almost exactly thanks to optical potentials fitted to the elastic scattering. C. Barbieri PRL103, (2009) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

18 Connecting reaction with structure. Ex: reduction of spectr. fact. S = S n S p 10 20MeV neutron & proton transfer vs breakup F. Flavigny et al., PRL110, (2013) Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

19 Beyond the drip line Proton unbound nuclei via invariant mass method Interest: Two-proton radioactivity vs. 2n-halo by isospin symmetry 5 He, 6 He, 8 He, 12 Be and IMME 6 Li. α. P T v z before Proton unbound nuclei T+1 5 Li α. CM after: α+p 6 Li, 7 Be, 9 C, 13 O studied by knockout of a deeply bound neutron: R. J. Charity & HiRA collabora5on. Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

20 Beyond the drip line Counts Data: R. J. Charity and the HiRA collabora7on, preliminary. Calcula7ons: G. Salvioni & AB (a) Be( Li, Li)X E/A = 36.6 MeV 5 Li g.s. p (b) Be( Be, Be)X Counts 5000 E/A = 65.2 MeV 6 Be g.s. 2p+ Counts (c) Be( C, C)X E/A = 63.8 MeV C g.s. 4p Counts (d) Be( O, O)X E/A = 28.5 MeV O g.s. 2p+ C E* [MeV] Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

21 Beyond the drip line Structure inputs: Shell model and ab initio Variational MonteCarlo SF SM by Mihai Horoi, private communication. SF VMC from R. Wiringa website ANC VMC from Kenneth M. Nollett and R. B. Wiringa, PRC83, (R) (2011). Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

22 Beyond the drip line E inc σ exp σ n σ p σ nnop r s A.MeV mb mb mb mb fm 6 Li 5 Li Be 6 Be C 8 C (-1p CB ) (22.3) C 8 B IAS Li 8 Li IAS O 12 O (-1p CB ) (-1p CB ) direct proton Coulomb breakup Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

23 Conclusions Inclusive breakup reactions are dominated by final state interaction with the target at small incident energy: use as surrogate reaction At intermediate incident energy: strong interplay between projectile and target characteristics: deformed momentum distributions and cutoff effects. PROTON TARGET? see A. Obertelli and T. Aumann talks... by the valence particle projectile momentum distribution at high incident energy: information on angular momentum of the initial state and possible dynamical core-target excitations Coincidence experiments of breakup particle experiments (using invariant mass method ) are more INdependent on incident energy but possible dependence on the initial state: necessity to link with methods discussed above and angular correlation of the decaying particles... : one the most interesting experiment to make...and interpret? Can enlighten different channels and reaction mechanisms. IN ADDITION Elastic scattering experiments and or total reaction cross section measurements: they can tell us about the typical interaction distances and help fixing the optical potentials. In the future more and more strongly bound nuclei will be studied at lower energies at ISOL-type facilities. In Europe: HI-Isolde, SPES, Spiral2, EURISOL (?). Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

24 Conclusions Some of my co-authors and collaborators in historical order. D. M. Brink N. Vinh Mau G. Blanchon F. Carstoiu G. F. Bertsch Ravinder Kumar MAGNEX collaboration at INFN-LNS F. Flavigny, A. Obertelli R. J. Charity G. Salvioni... see his talk at DREB2014 in Darmstadt Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25

25 Conclusions Angela Bonaccorso (INFN Sezione di Pisa) Reaction Dynamics for Light Dripline Nuclei Phys. Scr. T152 (2013) ARIS / 25