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Study of breakup mechanism of a loosely bound projectile
in a region of Coulomb breakup dominanceH. 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.)
The 19th International Conference on Few-Body Problems in Physics (FB19)Bonn, Germany, August 31 – September 5, 2009
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 = 07, n = 08 Analysis finite-range post-DWBA Summary & prospect
deuteron
Coulomb breakupconvenient way to imitate radiative capture at extremely low-E ?
p C D
~keV
radiative capture
Coulomb breakup
relevant to stellar-synthesis difficult direct-measurement
• small-c.s. at low-E• C can be unstable large cross section
due to high-flux at high-E proj.-fragmentation allows use of unstable beamsHowever,
virtual- also contributes to distortion (post-acceleration) nuclear interaction also contributes to breakupreliable treatment of reaction mechanism must be established.
p
C D
virtual-
A
smallrel-E
~100 MeV/A
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
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.
Deuteron
proton- energy spectra
However, in spite of long history of deuteron breakup, data with Coulomb-breakup dominance are rare.
Ep
H. Okamura et al.,Phys. Lett. B325 (1994) 308Phys. Rev. C 58 (1998) 2180
Previous data
First obs. of Coulomb b.u. dominance of deuteronat p ~ n = 0 & 56, 140, 270 MeVfor targets from 12C thru 208Pb
pure-Coulomb cals. (solid line) fairly wellexplain data, but...
pure-Coulomb cal.predicts complicated distributions,
which, however, were not observed in previous data.
n=0
E p
p
40Ca
118Sn
208Pb
40Ca
208Pb
p
n
10 10
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
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
Results Ed = 140 MeV, bin width 1 (0.5 @ = 0)
Results
small qlarge np
large qsmall 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
Ep=En
Ed = 140 MeV, bin width 1 (0.5 @ = 0)
Results
• Almost the same distributions with those of 12C• Larger cross section, approximately scaled by Z2
small qlarge np
large qsmall np
Ed = 140 MeV, bin width 1 (0.5 @ = 0)
Results
• Distributions change (only) slightly from 40Ca & 12C
small qlarge np
large qsmall np
Ed = 140 MeV, bin width 1 (0.5 @ = 0)
Results
• Drastic change of distributions; strong suppression @ 0 & n= p (opposite side) enhancement in neighboring (backward) angles
small qlarge np
large qsmall np
Ed = 140 MeV, bin width 1 (0.5 @ = 0)
An analysis finite-range post-form DWBA prior-form : large Vl contrib. CDCC
post-form : small remnant term DWBA ?
advantage in treatment of unbalanced Coulomb int.pure-Coulomb case
also from adiabatic approx.(+LMA?), J.A.Tostevin et al. PRC 57 (’98) 3225
local mom.approx.
n
p
A
r
R
n
p
A
r
R
troublesomecontinuum coupling
Nuclear interaction makes the problem a bit involved.
N.B. Baur & Trautmann (30 yrs ago) used Zero-Range Approx., while kd = 3.8 fm1 @ 140 MeV
Finite-Range calc. utilizing Coulomb-wave expansion& pure-Coulomb T-matrix
like plane-wave expd in DWUCK5for trans. reaction, e.g. (d,p)
q-integ. for each partial-wave l &angular integ. with Lebedev-Laikov grid
LMA
k
ExactDWBA
LMA
ExactDWBA
LMA
Validity of LMA was previously examined by comparison with Exact DWBAfor pure-Coulomb breakup
• reasonable agreement for (d,p n)• discrepancy becomes larger for (11Be,10Be n) M. Zadro PRC 66 (2002) 034603
Optical potentials for describing distorted-waves
H. Okamura et al., Phys. Rev. C 58 (1998) 2180
deuteron
Elastic-scatt. at 140 MeV werepreviously measure at RIKEN
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 & nusing global potentials
Too asymmetricN over-contrib.?
Results of F.R. post-DWBA pure-Coulomb &Coul.+Nucl.
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.)
N-dominant
N-dominant
C-dominant
Results of F.R. post-DWBA pure-Coulomb &Coul.+Nucl.
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.)
Results of F.R. post-DWBA pure-Coulomb &Coul.+Nucl.
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.)
Results of F.R. post-DWBA pure-Coulomb &Coul.+Nucl.
Pure-Coulomb cal. roughly account for data in whole region.Nuclear int. contributes differently from lighter targets.
Need more efforts to understand whole spectra.
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
destructive, because oforthogonality betweenbound & unbound states
Thank you for your attention
n-eff. & p-traj. were calibrated using 70-MeV p (H2+) beam
Bird View of RCNP Cyclotron Facility
ESS course
AVF
Ring
G-Raiden
N0
UCN(old)