TRANSFER REACTIONS ON 54Fe WITH A 80 MeV 16O BEAM

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TRANSFER REACTIONS ON 54Fe WITH A 80 MeV 16O BEAM

F. Pougheon, P. Colombani, H. Doubre, J.-C. Jacmart, P. Roussel, J.-C.

Roynette

To cite this version:

F. Pougheon, P. Colombani, H. Doubre, J.-C. Jacmart, P. Roussel, et al.. TRANSFER REACTIONS ON 54Fe WITH A 80 MeV 16O BEAM. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-249- C6-251. �10.1051/jphyscol:1971656�. �jpa-00214874�

JOURNAL DE PHYSIQUE Colloque C6, suppl&ment au no 11-12, Tome 32, Novembre-De'cembre 1971, page C6-249

TRANSFER REACTIONS ON 54Fe WITH A 80 MeV 6O BEAM

F. POUGHEON, P. COLOMBANI, H. DOUBRE, J.-C. JACMART, P. ROUSSEL and J.-C. ROYNETTE

Institut de Physique Nucltaire, Orsay, France

Rhume. - Des transferts d'un et de plusieurs nucleons sur le 54Fe sont etudies B l'aide d'un faisceau de ^{1 6 0} B 80 MeV. Toutes ces reactions sont trks selectives. On obtient dans le noyau final des niveaux d'6nergie d'excitation trbs elev6e dont les principales caract6ristiques peuvent &re dkduites.

Abstract. - The one and multi-nucleon stripping induced on 54Fe by a 80 MeV ^{1 6 0} beam has been investigated. All these reactions are very selective. High energy excitation levels of the final nucleus are obtained and main features of these levels can be deduced.

Experimental apparatus. - The variable energy cyclotron of Orsay which accelerates heavy ions up to an energy of 75(Zi)'/A is well suited for transfer reaction studies above the Coulomb barrier despite a rather poor energy resolution of the beam (- 700 key).

The incident energy of the ¹⁶⁰ beam used is 80 MeV and the intensity on the target (200 pg/cm2 self supporting 95 % enriched 54Fe) is about 50 nA.

In these experiments, the main difficulty is heavy fragment identification. The telescope used to detect the reaction products is made of two ORTEC surface barrier detectors (50 y and 350 ^p).

CARBON IDENTIFICATION SPECTRUM

= 3 0 0 p C

" C

"0 + ^"Fe

Lab = 20"

CHANNEL NUMBER

FIG. 1. - Detail of the identification spectrum corresponding to the various carbon channels.

A << Goulding ⁾⁾ identifier is used t o do the in-line control of the experiment and an IBM computer to analyse off line the whole E. AE map. All ions from Li to 0 are well separated and can be simultaneously stored for a wide range of excitation energy in the

final nucleus (10 to 25 MeV). A carbon identification is shown on figure 1.

Results and discussion. - I. ONE PROTON STRIPPING : 54Fe(160, 1 5 N ) 5 5 C ~ . - The 55Co spectrum is shown on figure 2. This stripping has been extensively

FIG. 2. - A 54Fe(160, 15N)55Co energy spectrum.

studied by (3He, d) [I], [2] but, due to the same momentum matching conditions (li - If

-

our spectrum is rather similar to the one obtained in (a, t) [3]. However in the heavy ion reactions the selection rules of Buttle and Goldfard [4] introduce a sort of ⁽⁽ j >) effect : for a same 1 value in (a, t) the two j ⁼ 1

+

17

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971656

C6-250 F. POUGHEON, P. COLOMBANI, H. DOUBRE, J.-C. JACMART, P. ROUSSEL AND J.-C. ROYNETTE 11. TWO-NUCLEON STRIPPING :54Fe(160, 1 4 N ) 5 6 C ~ ;

5 4 ~ ~ ( 1 6 0 , 1 4) 5 6 ~N i . - a) The (160, 1 4 ~ ) reaction is rather similar to the (a, d) one [5] in the selectivity for populating high spin states. The angular momentum transferred increases from 4 A to 10 A between 0 and 10 MeV of excitation energy. The 56Co spectrum is shown on figure 3. The highly populated levels lie

\ ,"" - .-

E = 80 MeV

CHANNEL NUMBER

FIG. 3. - (160, 14N),(160, 1%) energy spectra obtained by bombarding a 54Fe target with a 80 MeV 160 beam.

at 5.4, 6.5, 8.9, 11.8 and 13.7 MeV. The lowest lying states of 56Co are expected to be lp-lh [6] and they are not very excited by the two-nucleon trans- fer. Above, the 2p-2h states are preferentially excited and particularly the high spin ones ; in this way the 8.9 MeV level was assigned to the configuration [(nf7/2)-2 (vg912) (ng9/2)],+,1 by Lu et al. [5].

b) The 54Fe(160, 1 4 C ) 5 6 ~ i reaction has never been studied (Q = - 10 MeV) and the (3He, n) reaction has so far not been performed in the range of direct process energy. The 56Ni spectrum is shown on figure 3. The T = 2 56Fe isobaric analogue states a t about 10.0 MeV are slightly excited. Two highly populated levels lie at 12.1 MeV and 15.7 MeV and

are likely to be T = 1 analogue states of the 5.4 MeV

( 5 + ) and 8.9 MeV (9') levels in 56Co as it appears

on figure 4.

56 ~i Co

6 lab = 20'

FIG. 4. - Comparison of the 56C0 energy levels to the 56Ni ones. The 56C0 ground state (4+) is aligned with the analogue

6.4 MeV (4+) in 56Ni [7].

111. THREE-NUCLEON STRIPPING 54Fe(1 6 0 , 3C)5 7Ni.

- 57Ni spectrum is shown on figure 5. Highly popu- lated levels lie above the 5.2 MeV (T = 312). It is difficult at present to interpret these levels due to the lack of other stripping results a t high energy.

FIG. 5. - A 54Fe(160, 13C)57Ni energy spectrum.

N

150

.

: ¹⁰⁰

U P

-

U 5 0 .

IV. FOUR-NUCLEON STRIPPING 54Fe(160, 12C)5 'Ni.

- As well-known, the a transfer is a good tool for testing the four nucleon correlations in the nuclei, and the structure of the final nucleus 5 8 ~ i has been the subject of many theoretical (i. e. stretch model [8])

CHANNEL NUMBER

I _{n.0 l5.4 UJ 12.2 la6 9.0 6.0 5.24 3.2 0.0 0}

T-312

4

Y ~ e ( " ~ " ~ ) " ~ i LAB -15.

- ^{E -80 MeV} -

- -

-

-

w 15

10

5

I

250 300 350 400

TRANSFER REACTIONS ON 54FE WITH A 80 MEV 1 6 0 BEAM C6-251

and experimental investigations. In particular the same reaction has been studied by H. Faraggi et al. [9]

between 48 and 56 MeV incident energy. Our 58Ni

N -

d

c " ~ c ('$0 '*c 1 "NI 2

C -

-

c W

"9 a

0

100 10

so 5

250 300 350 400

CHANNEL NUMBER

FIG. 6. - A 54Fe(160, 12C)58Ni energy spectrum.

spectrum is shown on figure 6. As expected and as it was observed a t a lower incident energy the first levels of 58Ni which have essentially a two neutron configu- ration are not excited. Above and despite a large break-up background strong peaks appear between 8 and 17 MeV although at 48 MeV no strong peak was observed above 10 MeV. Jaffrin's calculation [9]

has shown that the first quasi-rotational bands (up to 10 MeV) are built with the ⁽⁽ quartet >> in the 2p1/2 and 2p 312 shells. The contribution of the If 512 orbit begins at higher energy because of a strong If 512 - If 712 repulsion and the l g 912 contribution would be pushed up t o even higher energies. The high excitation energy levels observed a t 80 MeV might be assigned to these shells.

In conclusion the stripping reactions induced by heavy ions well above the Coulomb barrier are still very selective and are a good tool for testing the level configurations and the nucleon correlations up to very high excitation energy.

References

[l] ARMSTRONG (D. D.) and BLAIR (A. G.), Phys. Rev., [5] Lu (C. C.) et al., Phys. Rev., 1969, 186-4, 1086.

1965, 140, 1226. [6] VERVIER (J.), Nucl. Phys., 1966, 78, 497.

[2] ROSNER (B.) and HOLBROW (C. H.), Phys. Rev., 1967, [7] SHERR (R.), Phys. Letters, 1967, 24B, 321.

154, 1080. ^[8] DANOS (M.) and GILLET (V.), Phys. Rev., 1967, 161, [3] ROUSSEL (P.) et al., Nucl. Phys., 1970, A 155, 306. 1034.

[4] BUTTLE (P. J. A.) and GOLDFARD (L. J. B.), NucZ. [9] FARAGGI (H.) et al., De Shalit memorial book. Annals

Phys., 1966, 7 8 , 409. of Physics.