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Submitted on 1 Jan 1971
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THE 54Fe(16O, 12Cγ)58Ni REACTION AT 48 MeV
P. Beuzit, R. Ballini, J. Delaunay, I. Fodor, J. Fouan, J. Gastebois
To cite this version:
P. Beuzit, R. Ballini, J. Delaunay, I. Fodor, J. Fouan, et al.. THE 54Fe(16O, 12Cγ)58Ni REACTION AT 48 MeV. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-139-C6-140.
�10.1051/jphyscol:1971621�. �jpa-00214839�
JOURNAL DE PHYSIQUE Colloque C6, supplkment au no 1 1 - 12, Tome 32, Novembre-De'cembre 1971, page C6-139
THE 54Fe(160, 12CY)58Ni REACTION AT 48 MeV
P. BEUZIT, R. BALLINI, J. DELAUNAY, I. FODOR (*), J. P. FOUAN and J. GASTEBOIS
Departement de Physique Nucleaire, C. E. N. Saclay, France
Rhumb. - Nous avons mesure les spectres gamma en co~ncidence avec les I2C emis dans la reaction 54Fc(160, 12Cy)jsNi. Les niveaux b 3,53 MeV ( 0 ' ) ct 4,47 MeV (3;) ont pu 6tre identifib.
Le pic intense observe vcrs 6,O McV correspond b l'excitation de plusieurs niveaux qui se desexcitcnt directement vers l'ttat fondamental.
Abstract. - The gamma spectra in coincidence with outgoing 12C in thc 54Fe(lW, 12Cy)sxNi were measured. Identification of the 3.53 (0+) and 4.47 MeV (3i.) levels was performed. The strong peak at 6.0 MeV corresponds to the excitation of several states decaying directly to ground state.
Recent experimcntal data [I], [2], [3] on electro- magnetic transitions on 58Ni cannot be accounted for by R. P. A. calculations [4], [S] in the frame of a simple shell model. It can reasonably be expected that higher order configurations involving both neutrons and protons play an important role. Such configurations could lead to high relative cross sections in many particle transfer reactions.
The quartet coupling scheme is asuccessful model for such configurations in light nuclei and its validity can be checked on the medium-A region by four-nucleon- transfer reaction. A large number of (160, 12C) experiments [6, 71 have been performed in the Fe, Ni, Zn region where this process exhibited higher cross sections than other reactions (e. g. (7Li, t)) and the spectra thus obtained exhibit an apparent high selectivity.
We have performed a 54Fe(160, 12Cy)58Ni experi- ment to test the possiblc identification of some excited levels with previously known ones through their gamma decay modes and determine some major characteristics of the observed peaks. The case of 58Ni is more favourable because we had determined the gamma decay scheme of most levels up t o 8 MeV, in the framework of a systematic study of even nickel isotopes [2], [5].
In such low cross section experiment the efficiency versus resolution compromise becomes very critical.
We thus used two different set-ups : a solid state counter telescope ( A E = 7 pm, E = 1 500 pm thick) was used for particle detection and identification : i) in coincidence with a large (5" x 6") NaI(TI) gamma detector the high efficiency of which allowed to select a small particle solid angle leading to 250 keV FWHM energy resolution ; ii) with a much larger solid angle, in order t o take advantage of the high gamma energy
(*) On leave from Institute for Nuclear Physics, Budapest, Hungary.
resolution but lower efficiency performances of an 80 cm3 Ge(Li) detector, the particle energy resolution was then of the order of 800 keV. In both cases the coincidence time resolution was of the order of a few nanoseconds and the recording of each event on magnetic tape allowed to take full advantage of the multidimensional data processing as described ear- lier [ 2 ] , [5]. The experiments were performed with a 300 nA beam of 48 MeV 1 6 0 ions accelerated in the Saclay FN model Tandem Van de Graaff. The 54Fe evaporated targets used were of the order of 200 pglcm2 thick and outgoing l Z C were detected around 45@
laboratory angle. The 1Na detector covered a large solid angle and the germanium diode was placed at 90° above the reaction plane in order to minimize Doppler shift and broadening of gamma lines. The salient features of our experimental data can be seen on figures 1 and 2 :
- the 3.5 MeV peak in the I2C spectrum can be identified with the known 3.53 MeV state which decays to the 1.45 MeV 2: level and is given J" = o+ [3];
- the 4.5 MeV peak corresponds t o the excitation of several 58Ni levels and among them the 4.47 MeV 3; is unambiguously identified through its decay t o the 2: state (3.02 MeV gamma line, Fig. 1).
At higher excitation energies precise identification of levels is not possible in the present experimental stage, nevertheless several facts come out :
Each peak (observed with 250 keV resolution) includes the excitation of several levels.
Some states around 5.5 MeV excitation decay to the 2.46 MeV 4:' state. The groups at 6.9 and 9 MeV exhibit gamma spectra similar to that of the 5.5 MeV and this corresponds to rather complex cascade decay modes.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971621
C6-140 P. BkUZIT, R. BALLINI, J. DELAUNAY, 1. FODOR, J. P. FOUAN ET J. GASTEBOIS
FIG. I . - 1 ZC spectra in coincidence with different gamma energy ranges selected on the INa(TI) spectrum. The comparison of these with the corresponding single spectrum drawn above,
shows theground state decays for the 6.0 MeV peak ( E y > 5 MeV) and the cascade decays for the 5.5, 6.9 and 9.0 McV groups
(enhancement in the 0.5 < E, < 5 MeV spectrum).
In conclusion, our data show that the spectrum obtained on such nucleus does not allow straight- forward interpretation as it is the case for light nuclei.
The rotational type cascade decay, predicted for quar- tet structure likely present, does not emerge from the gamma spectra we have obtained. The only regions where such decay characteristics could be found are the 5.5, 6.9 and 9 MeV. On the contrary, characteristics obtained for some of the most intense peaks exclude their belonging to such bands, e. g. the cross over to ground state indicates that the 6 MeV excited levels are not high spin members (J" = 4, 6 or 8') of such band. This added to the excitation of the collective 3;
state suggests that some core excitation is present.
In the present stage, where single spectra and angular distributions cannot yet lead to definite conclusions on the nature on the states excited, such gamma experi- ments may shed some light and help to understand the reaction mechanism which appears rather complex.
-.-, 5.9 MeV -Z E x < 6.L MeV
I l.W t L 5
5 M e V < E , c 59M+V
TRPINYTIONS .- TO 2 . 6 MeV (4'1
, ..["+:,,%,".l".
.i\ / , , ~*.~~~-,~~,d&.:-"-~ --,\.- tLk,A.. *-,L
On the contrary the intense 6 MeV peak is -. ~ M R Y < E, c L S M ~ Y
assoctated with high energy gamma lines, as can be
, d l + ; , L ,' L L? (3-1 - , 3 0 2
-
1 L5 [T)seen both on figures 1 and 2, they correspond to -. I ' m j A ,W*W.,~+~,'- - -. . - A- -- --, ground state cross over transitions from levels around 32MeV<EX<36MsV
5.9, 6.0 and 6.2 MeV excitation energies (similar - 3 5 3 ( 0 * ) - l L 5 (2'1 2 08
behaviour was found for a 7.4 MeV excited state). - , _ _ ---id-^
- - -
I-This can be tentatively compared with the 58Ni(p, p' y ) - e x -
results [2], [5] where ground state transitions were FIG. 2. - Germanium gamma spectra in coincidence with
found In the same energy region. selected 12C energy ranges.
References
[ I ] BERTIN (M. C.), BENCZER-KOLLER (N.), SEAMAN (G. C . ) [4] FEDERMAN (P.) and ZAMICK (L.), Phys. Rev., 1969, and MAC DONALD (J. R.), Phys. Rev., 1969, 177, 1534.
183, 964. [5] BEUZIT (P.), Thesis, Universite de Paris-Sud, 1971.
P] BEUZIT (P.), DELAUNAY (J.), FOUAN (3. P.) and RON- [6] CONSOLO (A.), LEMAIRE (M.-C.), MERMAZ (M.) and
SIN (H.), Nucl. Phys., 1969, A 137, 97. QUEBERT. This symposium.
[3] START (D. F. H.), ANDERSON (R.), CARLSON (L. E.), [7] MORRISON ( G . ) . this symposium.
ROBERTSON (A. G.) and GRACE (M. A.), NucI.
Phys., 1971, A 162, 49 and references therein.
