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)