16O LEVELS FROM THE TRANSFER OF THREE AND POUR NUCLEONS

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16O LEVELS FROM THE TRANSFER OF THREE AND POUR NUCLEONS

G. Bassani, N. Saunier, B. Traoré, G. Pappalardo, A. Foti

To cite this version:

G. Bassani, N. Saunier, B. Traoré, G. Pappalardo, A. Foti. 16O LEVELS FROM THE TRANSFER

OF THREE AND POUR NUCLEONS. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-135-C6-

137. �10.1051/jphyscol:1971620�. �jpa-00214838�

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JOURNAL DE PHYSIQUE

CoIloque C6, supplinzent au no 1 1-12, Tome 32, Novembre-Dkcembre 1971, page C6-135

1 6 0

LEVELS FROM THE TRANSFER OF THREE AND FOUR NUCLEONS

G . BASSANI, N. SAUNIER, B. M. TRAORE Dtpartement de Physique Nucltaire,

C. E. N. Saclay, France

and

G . PAPPALARDO and A. FOTI

(*)

Istituto di Fisica, I. N. F. N., Catania, Italy C. S. F. N.lS. M., I. N. F. N., Catania, Italy

RCsume. -

Nous presentons une discussion des niveaux de

^{1 6 0}

excites

A

I'aide des reactions

"C(6Li,

d) ^{' 6 0 ,}

lZC(7Li, t)16(9, l'C(bLi, t)lhO. Nous tenons compte aussi des rksultats publies obtenus

A

partir de reactions de transfert de deux nucleons. Ces experiences ont ete faites

ⁱⁱ

des Cnergics comprises entre

20

et

32

MeV.

Abstract.

^-

We present a discussion of

1 6 0

levels excited in the 12C(6Li, d)160, IZC(7Li, t)160, 13C(6Li7 t)lhO reactions taking into account also available two-nucleon transfer results. Experiments were performed at energies ranging from

20

to

32

MeV.

Quantitative spectroscopic measurements using H. I. induced reactions are rendered difiicult by the problems of the accurate description of the projectile, the reaction mechanism, etc. However the comparison of results obtained from different many nucleon trans- fer reactions leading to the same residual nucleus appears as a powerful tool to extract valuable infor- mations on states involving many particle excitations.

We present here a discussion of

^{1 6 0}

levels excited in the 12C(6Li, d)160, 1 2 C ( 7 ~ i , t)160, 13C(6Li, t ) I 6 0 reactions taking into account also the results obtained by Zisman et al. [I] using the two nucleon transfer reaction 14N(a, d)160. Experiments were perfor~ned at energies ranging from 20 t o 32 MeV using either a

AE-E

telescope associated with a particle identifying system or position sensitive detectors in the focal plane of a magnetic spectrograph.

Out of the many known

1 6 0

levels up to 22 MeV excitation energy only few are selectively excited in two-, three- and four- nucleon transfer reactions.

This is evidently the result of two concurring facts

:

first, certains levels even at very high excitation energy are made of a reduced number of configurations involving presumably only a given number of excited particles

;

secondly, the transfer reactions used are

(*) Visiting

Scientist

at thc

DCpartement

de

Physique Nucleaire, C.

E. N. Saclay,

France, according to

the

contract BT-11112.766 between the

C . E. N.

Saclay

and the C. S. F. N.1 S. M.,

Catania.

particularly adapted as far as the mechanism is concerned to investigate levels of the above type. Since the study of the t6Li, d) mechanism has shown that the excitation of strong peaks is mainly due to a direct four-nucleon transfer, different np-nh confi- gurations could be excited with this reaction. The results indicate that essentially only the members of the 4 p-4 h rotational band based on the 6.05 MeV, 0" level are preferentially excited [2]. Moreover the comparison with the (a, d) and (6Li, t) spectra (Fig. 1) shows that the mixing with 2 p-2 h configurations is negligible with an exception for the 10.35 MeV, 4- level. This result is in complete agreement with the microscopic calculations of Zuker et al. [3] which can reproduce the excitation energy of each member of the band with remarkable precision.

With the exception of the previously unknown strong 14.30 MeV level, the more prominent peaks in the (6Li, t) spectra are known to correspond to positive parity levels. Since also in this case the transfer appears as direct (this Symposium), the dominant configurations in these levels must be of the type 2 p-2 h , which is confirmed by the comparison with the (cr, d) data. The fact that known negative parity levels are not

selectively

excited suggests that 1 p-1 h and 3 p-3 h configurations are in general strongly mixed, in agreement with the above mentioned microscopic calculations. Particularly interesting appears to us the 14.30 MeV peak (Fig. 2) because of

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971620

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C6- 136 G . BASSANI, N. SAUNIER, B. M . TRAORE, G . PAPPALAKDO A N D A. FOTl

' 2 ~ ( 6 ~ i , d ) : 6 0

$

eLAs=l0'

=

EL, = 3 2 MeV

A

L

L.-!.J,

4 , J

4 6 8 10 12 14

ENERGY ( A U . )

,

¹⁰⁰ ENERGY( A.U.) ²⁰⁰

its strength and narrow width (r < 50 keV). The corresponding level, which has been observed so far only in the (6Li, t) reaction, should be rather pure with a dominant 3 p-3 h character.

Although the states preferentially excited in the (6Li, d) and ('Li, t) reaction are the same, the relative intensity may differ of factors up to 10 (Fig. 3).

FIG. 2. - Level structure in ' Q (14.0 < E* (MeV) < 15.0)

This suggests the importance of the role played by

from the 13C(6Li, t)160 reaction. These data have been taken

with position sensitive detectors and an energy resolution

the projectile in determining the magnitude of the

(FWHM) i 30 keV.

cross-sections and the need of detailed analysis of

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' 6 0 LEVELS FROM THE TRANSFER O F THREE AND FOUR NUCLEONS C6- 137

the reaction mechanism to derive correct spectroscopic transfers, we postulate the existence of one or more informations. On the basis of the form of the structure new wide levels involving the excitation of at least observed around 14.5 MeV in three- and four- nucleon two particles.

References

[I]

ZISMAN

( M .

S.), MCCLATCHIE

(E. A.) and

HARVEY (B.

G.), Phys.

Rev.,

1970 2C, 1271.

[2]

BASSANI

(G.),

PAPPALARDO

(G.),

SAUNIER

(N.) and

TRAORB (B.

M.), Phys. Letters, 1971, 34B, 612.

[3]

ZUKER

(A. P.),

BUCK

(B.) and

MCGRORY

(J.

M.),

PD99 and BNL-14085.