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AMD+GCM Study of Structure of Carbon Isotopes G. Thiamova

AMD+GCM Study of Structure of Carbon Isotopes G. Thiamova

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546

even-even and even-odd isotopes, respectively. The details concerning the basis

hnctions can be found in [2].

The binding energies are presented in Fig. 1. In general, good agreement is

obtained in all the studied region The binding energy of 12C is smaller than the

experimental value. It is partially due to the Majorana parameter M=0.6, fitted

to the binding energy of l 6 0 and known to produce underbinding of I2C. On the

other hand, the spin-orbit term seems to be too strong and thus the 3-alpha

component in the ground state wave function is too small. This is also reflected

in the smaller B(E2) transition strength (see below).

To describe a halo nucleus I5C is a real challenge for the AMD methods.

Here we do not reproduce the ground state spin 1/2+ . This is mainly due to the

simple interaction with no tensor term and strong spin-orbit term. However, in

[2] we have adopted a better description of the s-orbit for the odd neutron and

the excitation energy of the 112' decreased considerabely.

The systematics of the excitation energies of the 2'1 states clearly supports

the idea about N=16 magic number, reflected by large 2fl energy of 22C. The

(dj/2)6subshell closure predicted by our calculation but not seen experimentally

is again due to the stronger spin-orbit term, which pushes the dj/2 orbit down in

energy. A comparison is made with an AMD calculation [4] with weaker spinorbit term and modified Volkov interaction W 1 .

The B(E2 ) transition strengths (Fig.3) are compared with the experimental

data and the shell-model values [5] obtained with effective charges. Smaller

B(E2) value for I2C reflects most probably smaller 3-alpha component in the

ground state wave function due to stronger spin-orbit term. In I6,l8C protons

construct almost closed shell-model configuration so the B(E2) value is very

small. Proton contribution is recovered again in *OC. The very small B(E2) value

for I6C has been measured recently [6] and is successfully reproduced by our

model.



3. Summary

We have performed a systematic AMD+GCM calculation of structure of carbon

isotopes 12C-**C.We can reproduce fairly well a lot of experimental data. Here

we present the systematic calculation of binding energies, 2cI energies and

B(E2) strengths. Even though the effective interaction is simple and there are

indications that the spin-orbit term is too strong it should not change the

qualitative results of this analysis. From the systematics of 2+1 energies a clear

support for the N=16 magic number is given. B(E2) value of 12C is smaller due

to stronger-spin orbit term. Very small B(E2) value for I6C is successhlly

reproduced by our model.



547



References



N. Itagaki and S. Aoyama, Phys. Rev. C61,024303 (2000).

G. Thiamova, N. Itagaki, T. Otsuka and K. Ikeda, to be published.

N. Itagaki and S. Okabe, Phys. Rev.C61,044306 (2000)

Y. Kanada-En'yo and H. Horiuchi,, Prog. Theor.Phys..Suppl. 142, 205

(2001).

5. R. Fujimoto, PhD thesis, University of Tokyo, 2002

6. N. Imai and Z. Elekes, private communication



1.

2.

3.

4.



n



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z



110-



3/2'



M



C



calculation



A'



.3



8 5 .



I



12



.



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,



,

16



,



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.



18



Mass number



Figure 1 Expenmental and calculated bindmg energies of ''C -"C



I



20



.



I



22



548



i4



12



16



i6



22



20



Mass Number

Figure 2. Expenmental and calculated energies of the 2', states. A comparison is made with an

d weaker spin-orbit term.



AMD calculation with the MVl interaction i



60



1

-



50



-



40



-



A



AMD calculation

shell-model calculation



A



T



'xl



30-



20



-



10



-



0



0



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12



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I



14



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16



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Figure 3. Experimentaland calculated B(E2) transition strengths.



I



-



20



I



22



STUDY OF THE 26Si(p,y)27PREACTION BY THE

COULOMB DISSOCIATION METHOD



Y. TOGANO', T. GOMI', T. MOTOBAYASHI~,Y. ANDO', N. A O I ~ ,

H. BABA', K. DEMICHI', Z. ELEKES3, N. FUKUDA', ZS. FULOP3,

u. FUTAKAMI', H. HASEGAWA~, Y. HIGURASHI~,K. IEKI',

N. IMA12, M. ISHIHARA2, K. ISHIKAWA4, N. IWASA5, H. IWASAKI',

S. KANNO', Y. KOND04, T . K U B 0 2 , S. KUBON07, M. KUNIBU',

K. KURITA', Y. U. MATSUYAMA', S. MICHIMASA7, T. MINEMURA',

M. MIURA4, H. MURAKAMI', T . NAKAMURA4, M. NOTAN17,

S. OTA8, A. SAITO', H. SAKURAI', M. SERATA', S. SHIMOURA7,

T. SUGIMOT04, E. TAKESHITA', S. TAKEUCH12, K. UE6,

K. YAMADA', Y. YANAGISAWA2, K. YONEDA', AND A. YOSHIDA2

'Department of Physics, Rikkyo University, Tokyo 171-8501, Japan

R I K E N (Institute of Physical and Chemical Research), Saitama 351 -0198,

Japan

31nstitute of Nuclear Research of the Hungarian Academy of Science

(ATOMKI), 4001 Debrecen Hungary

Departm.ent of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan

Department of Physics, Tohoku University, Miyagi, 980-8578, Japan

Department of Physics, University of Tokyo, Tokyo 113-0033, Japan

7Center of Nuclear Study (CNS), University of Tokyo, Saitama 351-0198, Japan

Department of Physics, Kyoto Uni,uersity, Kyoto 606-8502, Japan

National Superconducting Cyclotron Laboratory, Michigan state Uniuersity,

East Lansing, Michigan 48824



'



'



The Coulomb dissociation of 27Pwas studied experimentally using 27Pbeams at 57

MeV/nucleon with a lead target. The gamma decay width of the first excited state

in 27P was extracted for astrophysical interest. A preliminary result is consistent

with the value estimated on the basis of a shell model calculation by Caggiano et al.



1. Introduction

Observation of galactic y rays using the satellite equipped with y telescope

indicates an intense 26A1distribution throughout the galactic plane The

26Si(p,y)27Preaction is one of the key reactions in nucleosynthesis of 26A1

in novae. The production of "A1 mainly depends on the reaction sequence



'.



549



550

24Mg(p,y)25Al(,B+v)25Mg(p,~)z6A1.

This production sequence can be bypassed by 25Al(p,y)26Si(p,y)27P.

It has been suggested that higher temperature novae ( T g FZ 0.4) may be hot enough to establish an equilibrium

between the isomeric state and the ground state of 26A1 Thus, 26Si destruction by proton capture is important to deterniine the amount of' the

gound state of 26A1 produced by the equilibrium, since the isomeric level

of 26AA1would be fed by the 26Si ,B decay. The 27Pproduction in novae

is dominated by resonant capture via the first excited state in 27Pat 1.2

MeV, because the state is close to the Ganiow window. However, there is

no experimental inforniation about the strength of resonant capture in this

reaction. Therefore, we aimed at detrmiining experimentally the ganinm,

decay width of the first excited state in 27P.



'.



Plastic

scintillator

hodoscope



osition sensitive



2.8 m



Figure 1.



Schematic view of the experimental setup.



2. Experimental Setup



The experiment was performed at the RIPS beam line at thc! RIKEN Accelerator Research Facility. A secondary beam of 27Pat 57 MeV/nucleon

was produced by the fragmentation of 115 MeV/nucleoii "Ar beams on a

300 111g/cni2 thick 'Be target. The 27Pbeam bombarded a 125 mg/cni2

thick lead target. A typical intensity and resultant purity were 1.5 kcps



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