THE C12(Li6, τ)N15 AND C12(Li6, t)O15 REACTIONS

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THE C12(Li6, τ)N15 AND C12(Li6, t)O15 REACTIONS

V. Chuev, V. Davidov, B. Novatskii, A. Ogloblin, S. Sakuta, D. Stepanov, V.

Timofeev

To cite this version:

V. Chuev, V. Davidov, B. Novatskii, A. Ogloblin, S. Sakuta, et al.. THE C12(Li6, τ)N15 AND C12(Li6, t)O15 REACTIONS. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-165-C6-166.

�10.1051/jphyscol:1971629�. �jpa-00214847�

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JOURNAL DE PHYSIQUE Colloque C6, suppkment au no 1 1 - 12, Tome 32, Novembre-Dkembre 1971, page C6-165

THE C12(Li6, z ) N l 5

AND C1 '(Li6, t)O1 REACTIONS

V. I. CHUEV, V. V. DAVIDOV, B. G . NOVATSKII, A. A. OGLOBLIN, S. B. SAKUTA, D. N. STEPANOV and V. A. TIMOFEEV

Kurchatov Institute of Atomic Energy, Moscou, USSR

Resume. - Les reactions ⁽⁽miroir ¹⁾CIz(Li6, He3)NIS et CIz(Li6, t ) 0 1 5 ont it6 Ctudiees a

E1.i6 = 30,8 MeV. Un mkanisme de transfert de trois nucleons rend compte des donntes. Le mkanisme du transfert d'agreats de He3 ou de triton ne se rnanifeste pas.

Abstract. -The 12C(6Li, r)lSN and lzC(6Li, t)lsO mirror reactions have been studied at Ee~r ^=:30.8 MeV. The data obtained are accounted for by a three nucleon transfer mechanism.

The mechanism of the transfer of He3 and T3 clusters does not manifest itself.

The (6Li, t) reactions observed on 'Be and 13C [I, 21 and 13C [3] a t the lithium ion energies above 20 MeV exhibited peculiar features. None of the mechanism reported [2] could completely explain the results.

First of all it was desirable to perform the parallel investigation of the (6Li, t) and (6Li, T) reactions pro- ducing mirror residual nuclei. In the present paper the 12C(6Li, r)15N and 12C(6Li, t)150 reactions were studied a t ELi = 30.8 MeV.

The spectra of the outgoing nuclei 3He and 3T in both reactions (Fig. 1) are very similar within the whole excitation energy range investigated. The angular distributions of 3He and 3T (Fig. 2) corresponding

FIG. 1.- Energy spectra from the IzC(bLi, t)lsO and

ClZ(Li6, He3)N 15 reactions.

to the production of 15N and ¹⁵⁰mirror states are also similar with a reasonable accuracy, the cross sections of 3He production being higher than those of 'T production. The ratio between these cross sections increases from the unity for E* -- 5 MeV to 2 for E*

-

13 MeV. The total picture of the angular distributions obtained is characteristic of the direct transfer processes.

Possible direct mechanisms in the (6Li, r) and (6Li, t) reactions can be either the three-nucleon transfer (in the form of three uncorrelated nucleons or, taking into account the 6Li structure, in the form of a deuteron and nucleon) or the transfer of 3He or 3T clusters (Fig. 3). The latter mechanism can take place since there is an evidence [4] that the 3He + 3T cluster configuration is present in the wave function of the 6Li ground state.

The spectra of the (6Li, 7) and ( 6 ~ i , t) reactions show that the excitation of most states o f "N and

150 nuclei can be understood in the framework of the three-nucleon transfer mechanism. Indeed, the states with different parities having the (p 1/2)2 (sd)' and (p 112)' (sd)' configurations are formed with moderate probability. Some enhancement in the transitions to the states of (p 112)' (sd)' type is observed. This can be treated as the transfer of a deuteron and a nucleon because the states with ( ~ d ) ~ configuration are strongly populated by the deuteron transfer process, such as the (6Li, z) reaction [2]. Intense groups corresponding to the excitation energies of 8.9 MeV ("0)-9.2 MeV ("N) and 9.5 MeV ("0)- 9.8 MeV (15N) are examples of such transitions. In all the above cases there is a good agreement with the ('Li, a) reaction [5], where the three-nucleon transfer is the main mechanism in the excitation of low-lying states.

The data obtained indicate that the 'He or 3T cluster transfers do not dominate in the ( 6 ~ i , t) and (6Li, T) reactions. The pole mechanism must be

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971629

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V. I. CHUEV, V. V. DAVIDOV, B. G. NOVATSKII

FIG. 2. - Angular distributions of the 12C(6Li, t)lSO and I2C(6Li, 3He)lSN reactions.

highly selective since the states with a strong overlap with core + 3T o r core + 3He cluster model states occur rather rarely. The states exhibiting such a structure were found [5, 61 a t the excitation energies

1. t- ^or3 ~ e - c l u s t e r transfer

FIG. 3. - Feynman graphs corresponding to the triton cluster transfer and the three-nucleon transfer mechanisms proposed

for the (GLi, 3He) reaction.

near thresholds. This means that the character of the spectra of the ( 6 ~ i , 7) a n d ( 6 ~ i , t) reactions in the vicinity of thresholds is sensitive t o the existence of the cluster transfer mechanism. Various lithium- induced reactions, indeed, exhibit very strong transitions in the threshold excitation range [2]. In parti- cular, the transition in the 12C('Li, z ) l 5 N reaction t o the state of lSN a t the excitation energy of 14.9 MeV (the threshold 15N ^-+ 12C + t is in the vicinity of 15 MeV) is the strongest one [5]. l t is seen from figure 1 that the states of "N and "0 nuclei a t excitation energies of about 15 MeV are not excited a t all in the ( 6 ~ i , 7) a n d ( 6 ~ i , t) reactions. The 3He and 'T clusters are not observed t o be formed either in the dissociation process of 6Li. The upper limit of the cross section of the reaction 6Li + 3He + 3T (1 nibarn/ster a t small angles) was found from the measured spectra and proved t o be three orders of magnitude lower than the cross section of the dissociation reaction 6Li ^-+a + d and 6Li + a + p + n.

The values of the binding energies can not account for such a large difference.

Thus in a series of experiments (the (6Li, t) a n d (6Li, ^T)transfer reactions, the dissociation reaction 6Li ^-+3He + T, the elastic scattering 6Li + 3He [7]) the cluster structure 6Li = 3He + 3 T was not revea- led.

References

[I] GLUKHOV (Yu. A.), GOLDBERG (V. Z.), DAVIDOV [4] KURDYUMOV (I. V.), NEUDATCHIN (V. G.), SMIR- (V. V.), NOVATSKII (B. G.), OGLOBLIN (A. A.), ^NOV(Yu. F.), Phys. I ~ t t e r s , 1970, 31B, 426.

SAKUTA (S. B.), STEPANOV (D. N.), CHUEV (V. I.), ^{[ S ]}GLUKHOV (Yu. A.), NOVATSKII (B. G.), OGLOBLIN The Abstracts of the 19-th Meeting on Nuclear (A. A.), SAKUTA (S. B.), STEPANOV (D. N.), Spectroscopy, Yerevan, 1969, vol. 2, p. 61. Izv. Acorl. Naltk U S S R , phys. series, 1969, 33, [2] OGLOBLIN (A. A.), Proceedings of International Confe- 601.

Fence on Nuclear Reactions with Heavy Ions, [GI GLUKHOV (Yu. A.), NOVATSKII (B. G.), OGLOBL~N

Heidelberg 1969. (A. A.), SAKUTA (S. B.), STEPANOV (D. N.),

CHUEV (V. I.), Nucl. Phys. ( U S S R ) , 1971, 13, [3] BASSANI ( G . ) , KRUSE (T. H.), SAVNIER (N.), SOIJCHEKE _277.

(G.), Phys. Letters, 1969, 30B, 621. [7] CHUEV (V. I.) et al., This Conference.