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Study of breakup mechanism of a loosely bound projectile in a region of Coulomb breakup dominance

deuteron. The 19th International Conference on Few-Body Problems in Physics (FB19) Bonn, Germany, August 31 – September 5, 2009. Study of breakup mechanism of a loosely bound projectile in a region of Coulomb breakup dominance. H. Okamura , K. Hatanaka, A. Tamii (RCNP)

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Study of breakup mechanism of a loosely bound projectile in a region of Coulomb breakup dominance

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  1. deuteron The 19th International Conference on Few-Body Problems in Physics (FB19) Bonn, Germany, August 31 – September 5, 2009 Study of breakup mechanism of a loosely bound projectile in a region of Coulomb breakup dominance H. Okamura, K. Hatanaka, A. Tamii (RCNP) K. Sekiguchi, K. Suda (Nishina Center, RIKEN) H. Sakai, K. Yako, T. Uesaka, T. Saitoh (Univ. Tokyo) T. Wakasa (Kyushu Univ.) Y. Maeda (Miyazaki Univ.) K. Itoh, T. Ikeda, H. Kumasaka, R. Suzuki (Saitama Univ.) • Outline: • Introduction • Coulomb-breakup & deuteron • previous study at p=n=0 & Ed=56,140,270 MeV  its defects • Experiment • Result for 12C, 40Ca, 90Zr, 208Pb at p=0-7,n=0-8 • Analysis  finite-range post-DWBA • Summary & prospect

  2. C D p ~keV radiative capture Coulomb breakup convenient way to imitate radiative capture at extremely low-E ? ~100MeV/A p small rel-E D C virtual- A • relevant to stellar-synthesis • difficult direct-measurement • small-c.s. at low-E • C can be unstable Coulomb breakup • large cross section • due to high-flux  at high-E • proj.-fragmentation allows • use of unstable beams • However, • virtual- also contributes to distortion (post-acceleration) • nuclear interaction also contributes to breakup • reliable treatment of reaction mechanism must be established.

  3. Deuteron • one of the most loosely bound (stable) nuclei • well understood wave func. w/o resonance (direct breakup) • distinctively different nuclear & Coulomb breakup spectra • in 1st order proton- energy spectra • while • large post-acceleration effect  large Z/m diff. • large nuclear breakup contrib.  small Zp • These features will be useful • for detailed study of breakup mechanism. Ep However, in spite of long history of deuteron breakup, data with Coulomb-breakup dominance are rare.

  4. First obs. of Coulomb b.u. dominance of deuteron at p ~ n = 0 & 56, 140, 270 MeV for targets from 12C thru 208Pb pure-Coulomb cals. (solid line) fairly well explain data, but... Previous data H. Okamura et al., Phys. Lett. B325 (1994) 308 Phys. Rev. C 58 (1998) 2180

  5. p pure-Coulomb cal. predicts complicated distributions, 40Ca n=0 40Ca p Ep 10 ~ +10 n 208Pb 118Sn which, however, were not observed in previous data. 208Pb

  6. Previous Setup @RIKEN SMART • Q-Q-D focus-type spectrograph resulted in • poor (vertical) angular resolution for proton (avr. 2.2) • limited angular acceptance for neutron

  7. Present Setup @RCNP ESS-course Ed =140 MeV Simple C-shaped dipole-mag. allows 40 < Ep < 100 MeV 0 < p < +10 10 < n < +10 in coplanar geom. utilizing bend. mag. of old WN course

  8. Ed=140 MeV, bin width 1 (0.5 @ =0) Results

  9. Ed=140 MeV, bin width 1 (0.5 @ =0) Results Ep=En largeq smallnp smallq largenp • Double-peak atp=n= 0 w/ sharp dip at Ep=En(np =0) • Rapid change of shape depending on  • Opposite side (smaller q, larger np) favored

  10. Ed=140 MeV, bin width 1 (0.5 @ =0) Results largeq smallnp smallq largenp • Almost the same distributions with those of 12C • Larger cross section, approximately scaled by Z2

  11. Ed=140 MeV, bin width 1 (0.5 @ =0) Results largeq smallnp smallq largenp • Distributions change (only) slightly from 40Ca & 12C

  12. Ed=140 MeV, bin width 1 (0.5 @ =0) Results largeq smallnp smallq largenp • Drastic change of distributions; • strong suppression @ 0 & n=p (opposite side) • enhancement in neighboring (backward) angles

  13. An analysis  finite-range post-form DWBA p r R n A p r n R A • prior-form : large Vl contrib.  CDCC troublesome continuum coupling Nuclear interaction makes the problem a bit involved. N.B. Baur & Trautmann (30 yrs ago) used Zero-Range Approx., while kd = 3.8 fm-1 @ 140 MeV • post-form : small remnant term  DWBA ? advantage in treatment of unbalanced Coulomb int. pure-Coulomb case local mom. approx. also from adiabatic approx.(+LMA?), J.A.Tostevin et al. PRC 57 (’98) 3225

  14. Finite-Range calc. utilizing Coulomb-wave expansion & pure-Coulomb T-matrix like plane-wave expd in DWUCK5 for trans. reaction, e.g. (d,p) LMA q-integ. for each partial-wave l & angular integ. with Lebedev-Laikov grid k

  15. Exact DWBA Exact DWBA LMA LMA Validity of LMA was previously examined by comparison with Exact DWBA for pure-Coulomb breakup • reasonable agreement for (d,pn) • discrepancy becomes larger for (11Be,10Ben) M. Zadro PRC 66 (2002) 034603

  16. Optical potentials for describing distorted-waves deuteron Elastic-scatt. at 140 MeV were previously measure at RIKEN H. Okamura et al., Phys. Rev. C 58 (1998) 2180 Consistent with recent global-potential H. An & C. Cai, Phys. Rev. C 73 (2006) 054605 proton & neutron Several global-potential are available in this region A.J. Koning & J.P. Delaroche, Nucl. Phys. A 713 (2003) 231 N.B. energy-dependence is taken into account for ejectiles p & n using global potentials

  17. pure-Coulomb & Coul.+Nucl. Results of F.R. post-DWBA Too asymmetric N over-contrib.? C-dominant N-dominant N-dominant Pure-Coulomb cal. account for data at 0 & small q. Nuclear int. improves at (some) backward angles (for n), but makes double-peak much too asymmetric (over-contrib.)

  18. pure-Coulomb & Coul.+Nucl. Results of F.R. post-DWBA Pure-Coulomb cal. account for data at 0 & small q. Nuclear int. improves at (some) backward angles (for n), but makes double-peak much too asymmetric (over-contrib.)

  19. pure-Coulomb & Coul.+Nucl. Results of F.R. post-DWBA Pure-Coulomb cal. account for data at 0 & small q. Nuclear int. improves at (some) backward angles (for n), but makes double-peak much too asymmetric (over-contrib.)

  20. pure-Coulomb & Coul.+Nucl. Results of F.R. post-DWBA Pure-Coulomb cal. roughly account for data in whole region. Nuclear int. contributes differently from lighter targets. Need more efforts to understand whole spectra.

  21. Summary & Prospect • (d,pn) elastic breakup has been measured at Ed=140 MeV, • 40Ep 100 MeV, 0p+10, -10n+10, • with a resolution  0.5, for 12C, 40Ca, 90Zr, 208Pb. • Observed double-peak at 0 ( Coulomb b.u. dominance) and complicated ang.-dist., which are NOT scaled by Z2, even drastic change between 208Pb and lighter targets.  critical test ground for breakup reaction theory • Finite-range post-form DWBA cal. has been made. Pure-Coulomb cal. roughly accounts for p=-n (q~0) data. Nuclear int. improves larger  data, but overestimates contrib. presumably due to p-n FSI (Vnp treated perturbatively). Better treatment is necessary also for heavier system breakup Thank you for your attention destructive, because of orthogonality between bound & unbound states

  22. n-eff. & p-traj. were calibrated using 70-MeV p (H2+) beam

  23. ESS course N0 Ring AVF G-Raiden Bird View of RCNP Cyclotron Facility

  24. UCN (old)

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