The Coulomb dissociation of 14Be 宋玉收 哈尔滨工程大学 2013.1 上海.

The Coulomb dissociation of 14Be

宋玉收哈尔滨工程大学

2013.1 上海

Contents

• The background and the motivation

• The objective

• The contents of the experimental research

• Experiment solution

• Beam application

The background and the motivation

• Low-lying dipole excitation mechanism;• Scarcity of experimental results and large

uncertainty of existed experimental data (14Be);• Theoretical calculation need more experimental

support– Different from 11Li and 6He, three-body model or five-

body model; – valence neutron and excited-core configuration ;

• Coulomb excitation has larger cross section and is feasible for drip-line nuclei research at RIBLL;

68Ni、 130,132Sn

M. Labiche et. al, prl86.600.2001

Coulomb dissociation

prl86.600.2001

1. Large uncertainty of the exp. data;

2. No quantitative spectroscopic factor discussion in detail;

3. The peak position and integration of the energy spectrum deviate from the theoretical result;

4. No 2-n correlation discussion;

1. Invariant mass spectrum;

2. Large (2s1/2)2 admixture;

prl86.600.2001, npa658.31.1999

3. Enhanced low-lying strength of E1;

Microscopic calculations

(Cluster dynamics)

prc52.704.1995, prc53.708.1996

Quantum Monte Carlo A-nucleon calculations

(Many-body problem)

npa654.157c.1999

semi-phenomenological description (npa706.48.2002)

•S2n (exp.) and Rrms (exp.) →

S2n=0.9MeVspectrum (exp.) peak position+ model

•The narrow B(E1) shape is quite different from other Borromean halo nuclei;

•vary the binding energy, the radius, and the admixture of different components of WF;

•initial and final state WF considered;

S2n=0.9MeV S2n=1.34MeV S2n=1.34MeV, Rrms=3.10±0.15fm

spectrum (exp.) peak position+ model

•Integration of the excitation strength

Similar as 8He and more complicated than 11Li, 6He.

s01/2

0p3/2

0p1/2

1s1/2

0d5/2

n

complicated core structure should be considered

closed p shell

14Be S2n

13Be 0d5/2

13Be s-wave bound state

closed p shell?magic number loss or

excited core?

In 2000’s 14Be Coulomb break up (14Be+Pb)prl86.600.2001

14Be nuclear break up (14Be+C, 14Be+p)•Rrms=3.25±0.11fm, npa875.8.2012

•The first 2+ state of 14Be, plb654.160.2007

•cluster breakup of 14Be, prc70.024608.2004

•systematic study of 14Be+C, npa791.267.2007

Coulomb dissociation of Heavier nuclei close to neutron drip line

•31Ne Coulomb Breakup,PRL 103, 262501 (2009)

•19,20,22C Nuclear Breakup, N.Kobayashi et al., PRC, in press

•Kinematically complete measurement of Coulomb Breakupof 22C, 19B, Production of 25,26O @SAMURAI@RIBF May 2012

The objective

• The correlation (spatial) of two valence neutrons by sum rule;

• Spectroscopic factor of 2s1/2 and 1d5/2;• To verify the two-neutron bonding energy S2n;

• To discuss the reasonability of 3-body and 5-body14Be model by the energy spectrum and neutron-removal cross section;

• 12Be core is inert or not;• To understand systematically about the soft E1

excitation of 2-n halo nuclei like 6He, 11Li, 14Be;

2 / ddn relS E npa706.48.2002

The contents of the experimental research

• The kinematically complete measurement of the break up of 14Be on Pb target;

• The angular distribution of 12Be+n+n in mass center coordinate;

• Angular distribution of valence neutrons;• To reconstruct the invariant mass spectrum of 14Be;• To eliminate the nuclear interaction contribution from the

transition strength by neglecting non-peripheral collision;• To obtain the reduce transition strength B(E1) by the virt

ual photon model;

12Ben

n

14Be

1np

12Be

n

n2np

Be12p

12Ben

n

Pb (high Z target )

Invariant Mass M

14Be

14Be*

12Be+ n+n

22 )()( baba PPEEM

)( barel MMME

Excitation Energy E*

2* rel nE E S

EMD reconstruction11Li

Spectroscopic factor

Energy weighted sum rule (EWSR ,non-model dependent)

1

1

exp

th

SS

SF

prc70.054606.2004

221

2

)(4

3)1( rr

A

ZeEB

)cos( 1221

22

21 rrrr

Non-correlated (independent particle model, 12=90 。 )

r1=r2=r (3-body cluster calculation )

12=?90 degree 2n correlated?

Non-energy weighted sum rule (NEWS)

npa542.310.1999

EMD on Pb

simulationM. Labiche et. al, prl86.600.2001

n-n correlated

jkps61.27.2012

Inert core?

npa875.8.2012, Rmexp=3.25±0.11fm

discrepancy

S2n

core

-exc

ited

prob

abili

ty

the relation between binding energy, spectroscopic factor, and deformation coefficient .

Experiment solution• Experimental setup

– PPAC– Forward ion telescope– MunCos

Pb targetPPAC

Si CsI

MuNCos

level scheme of 12Be

• Some problems to be pay more attention– No gamma detector presented;– 14Be、 12Be particle identification, and coincidence between production ions

and neutrons;– The influence of neutrons produced in the telescope on the detection of the br

eak-up neutrons;– Position resolution and efficiency of detectors ahead target;– Target thickness

Beam application

200enA 的 18O 作为入射初级束， 3500um 的 9Be 作为初级靶，降能器为 2000um 的 Al，分离提纯后的 14Be，能量为 35AMeV，能量展宽约 8MeV（ ~1.6%），流强约为 20 pps.

24 23N 2.3 10 20 3600 0.6 / 207.2 6.022 10 5%

14.4 (/ )hour

＝＝

24

23

2

2.3 10 14Be dissociation cross section (2.3b)

20 3600 14Be beam intensity 20pps

0.6 / 207.2 6.022 10

thickness of Pb target 0.6g/cm ,

Pb

360

mass number 207

0 /s h

.2g/mol

5% two-neutron efficiency of MuNCos

14.4/hour*200hour=2880

Thanks