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Submitted on 1 Jan 1971
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THE (6Li, t) REACTION MECHANISM
G. Bassani, N. Saunier, B. Traoré, G. Pappalardo, A. Foti
To cite this version:
G. Bassani, N. Saunier, B. Traoré, G. Pappalardo, A. Foti. THE (6Li, t) REACTION MECHANISM.
Journal de Physique Colloques, 1971, 32 (C6), pp.C6-133-C6-134. �10.1051/jphyscol:1971619�. �jpa- 00214837�
J O U R N A L DE P H Y S I Q U E Colloque C6, supplkment au no 11-12, Tome 32, Novembre-De'cembre 1971, page C6-133
THE (6Li, t) REACTION MECHANISM
G . BASSANI, N. SAUNIER, B. M. TRAORE DBparlement de Physique NuclCaire
C . E. N. Saclay, France
and
G. PAPPALARDO (*) and A. FOTI (**)
DCpartement de Physique NuclCaire C . S. F. N./S. M., I. N. F. N., Catania, Italy C. E. N. Saclay, France
RbumB. - Nous avons etudie le mkanisme de la reaction (6Li, t) pour des Cnergies de 6Li allant de 20 i 32 MeV. Les resultats obtenus montrent que dans le cas des niveaux les plus forte- ment excites le mecanisme dominant est un transfert direct de trois nuclbns.
Abstract. - The (6Li, t) reaction mechanism has been investigated in the 20 to 32 MeV energy range. The results obtained using 11B, 12C and 13C as targets indicate that the dominant mechanism for the excitation of strong peaks is a direct three-nucleon transfer.
As a continuation of our study of the (6Li, t) reactions [I], we have investigated the "B(6Li, t)14N, 1ZC(6Li, t)150 and '3C(6Li, t)160 reactions at a 6Li energy ranging from 20 t o 32 MeV. The discussion will be centered around the reaction mechanism. The emitted particles were identified using a AE-E telescope. Energy resolution (FWHM) was of the order of 80 keV at forward angles.
The (6Li, t) reaction appears to be characterized by the following features :
1. Selectivity. - Strong isolated peaks are present in the spectra in the energy range investigated i. e. up to 15-20 MeV excitation energy. A spectrum obtained from the '2C(6Li, t)150 reaction is shown in figure 1 where only few of the known ''0 levels appear to be strongly excited.
The results obtained from the ( 6 ~ i , t) reactions leading to the 14N and 160 residual nuclei suggest that when a proton is transferred to the lowest available orbital, the remaining proton-neutron pair is transfer- red as in the (a, d) reaction on the corresponding (2 + 1) target. This applies to some of the most prominent peaks. The 14N(a, d)160 [2] and
1 3( 6 L i ~ , t)160 Spectra are compared in figure 2 to show to which extent there exists a corres- pondence between the two reactions. Particularly
(*) lstituto di Fisica, I. N. F. N., Catania, Italy.
(**) Visiting Scientist at the Departement de Physique Nucldaire, C . E. N. Saclay, France, according to the contract
BT-I1/12.766 between the C. E. N. Saclay and the C. S. F. N.!
S. M. Catania.
interesting appears to us the intense 14.30 MeV level in 160 which as far as we know has been observed only in the ( 6 ~ i , t) reaction.
ENERGY ( A.U.)
2. Angular distributions behaviour. - Angular distributions typically exhibit some structure and pronounced forward peaking. This is particularly true for the most strongly excited peaks (Fig. 3). Few angular distributions with a ,8, = 90° symmetry have been obtained in the case of weakly excited levels.
3. Excitation functions behaviour. - Excitation functions have been measured at ,,8, = 150 from 20 to 32 MeV incident energy in 1 MeV steps for the reactions leading to ''0 and 160. They exhibit a
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971619
l 4 ~ ( d , d )160
400 - oLbB= 10.
E, -40MtV 300 -
2 0 0 -
rather smooth behaviour, the cross-sections decreasing regularly as the 6Li energy increases. The cross-sections are reduced by approximately a factor 3 in the energy range investigated.
On the basis of the above results it appears that contributions to the (%i, t) transition amplitude due to a direct three-nucleon transfer are certainly domi- nant for the most intense peaks observed in the spectra.
In order to evaluate the magnitude of the contribu- tion to the measured cross-sections from a compound nucleus mechanism, calculations were made using a reaction model based on the Hauser-Feshbach formalism. A comparison between experimental and calculated cross-sections relative to the 13C(6Li, t) I 6 0 reaction is shown in figure 3. It clearly appears that the calculated cross-sections are in most cases much smaller than the experimental ones especially in the forward region. Similar results have been obtained
in the case of the 12C target and for the excitation functions. This thorough investigation of the (6Li, t) reaction mechanism indicates that this reaction should be considered as a new extremely useful spectroscopic tool. Several previously unknown levels have been observed in the 14N, ''0 and 160 residual nuclei.
Valuable qualitative ideas on the important confi- gurations in the wave-functions of strongly excited states may be inferred from the comparison with theoretical calculations or other many-nucleon transfer reactions. Quantitative spectroscopic informations can be obtained only using a finite range DWBA code. Some preliminary results are presented in an other contributed paper.
ENERGY ( A U )
FIG. 3. - Comparison between the experimental angular distri- butions from the 13C(6Li, t)160 reaction at 28 MeV and the
results of the Hauser-Feshbach calculations.
References
[I] BASSANI (G.), KRUSE (T. H.), SAUNIER (N.) and Sou-
CHERE (G.), Phys. Letters, 1969, 30B, 621.
BASS AN^ (G.), CALAMAND (A.), PAPPALARDO (G.), SAUNIER (N.) and T R A O R ~ (B. M.), J . Physique, 1970, 31, C2-176.
[2] ZISMAN (M. S.), MCCLATCHIE (E. A.) and HARVF,Y ( B . G.), Phys. Rev., 1970, 2C, 1271.
