HIGH-SPIN HIGHLY-EXCITED STATES IN 20Ne AND THEIR POSSIBLE CLASSIFICATION

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HIGH-SPIN HIGHLY-EXCITED STATES IN 20Ne AND THEIR POSSIBLE CLASSIFICATION

A. Panagiotou, H. Gove, S. Harar

To cite this version:

A. Panagiotou, H. Gove, S. Harar. HIGH-SPIN HIGHLY-EXCITED STATES IN 20Ne AND THEIR POSSIBLE CLASSIFICATION. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-241-C6-243.

�10.1051/jphyscol:1971654�. �jpa-00214872�

JOURNAL DE PHYSIQUE Colloque C6, supplbment au no 11-12, Tome 32, Novembre-Dgcembre 1971, page C6-241

HIGH-SPIN HIGHLY-EXCITED STATES IN ONe AND THEIR PO S SIBLE CLA S SIFICATION

A. D. PANAGIOTOU (*), H. E. GOVE and S. HARAR (**) Nuclear Structure Research Laboratory, University of Rochester, Y., U. S. A.

Rbume. - La reaction 12C

+

12C ^{-+ a1}

+

20Ne* + a2

+

^{1 6 0} a kt6 utiliske pour mesurer les spins de quelques Ctats a haute knergie d'excitation dans 2oNe. Des corrdations angulaires ont ete obtenues en utilisant deux dktecteurs a localisation. Deux des nouveaux niveaux, 5-(15,9 MeV) et 7-(18,15 MeV), peuvent &re des membres de la bande K = 0- de la symetrie SU3 (86), et seraient dus a I'excitation a trois particules du cceur. Les resultats des expbiences

160(16Li, d)20Ne et 160(7Li, t)2oNe sont prksentCs et discutks.

Abstract. - The reaction 12C

+

^{12C + a 1}

+

^{20Ne* + a2}

+

^{1 6 0} was employed in the measu- rements of the spin of highly excited states in 2oNe. Angular correlations were obtained using two position sensitive detectors. Two of the new levels, namely the 5- (15.9 MeV) and the 7- (18.10 MeV), may belong to the K ⁼ 0- band of the (86) SU3 symmetry, arising from three- particle core excitation. Results obtained from the 160(6Li, d)2oNe and 16G(7Li, t)20Ne experi- ments are presented and discussed.

The reaction 12C(12C, al, a2)160 g . ~ . has been used ^foe ANGULAR CORRELATION

in the past by the Chalk River group in numerous spin ^'aN< E,.c = 5 0 MeV ^{18 l ~STATE e ~}

determinations of levels in ,ONe up to about 13 MeV ^{DECAY TO} _{a p =} ^{1 6 ~ Q S}

J - 7

excitation. We extended these measurements to the region between 15 and 18.2 MeV excitation.

The zero degree geometry of Litherland [ l ] was employed in our measurements. Two position sensitive detectors were used, one in the magnetic spectrograph at 00, detecting a,, and the other in the scattering chamber, detecting a,. A grid was placed in front of the 2

detector in the scattering chamber, defining 16 angles ^{b* 3 0 . ,mo-}

at about 2.750 intervals. ^m S

The following spin and parity determinations were made on the basis of the angular correlations :

The states 5- and 7- decay strongly to the ground

state and 1" doublet (Of, 3 3 of ¹⁶⁰ and weakly ^{FIG. 1.} - Angular correlations and fit for the 18.1 MeV level (7-).

to the 2nd doublet (2+, 1 -). Coincidence measurements at O0 determined the decays to go entirely to the

3-(6.131 MeV) member of the doublet. The decays two States together with the tentative (I-) 12.42 MeV to the 2nd doublet appeared to go to the 1- member, and (3-) 13.69 MeV [2] and the 9- a t 21.1 MeV [3]

although direct measurements were not done. These are suggested to belong to the K ⁼ 0- band of the (86) SU, symmetry, arising from three-particle-core 9-(15.18 ^f .04 MeV) 8 + (15.9

+

^{.04 MeV) ,mo}

5-(15.9 f .04 MeV) 7-(18.1 f .04 MeV) The two levels, 5- and 8', at 15.9 MeV were strongly excited at 50 and 51 MeV incident energy respectively.

Figure 1 shows a sample of the angular correlations

excitation.

(*) Present address : University of Oxford, Nuclear Physics In the cc quartet structure >> framework, the [2201 Laboratory Keble Rd., Oxford, England.

(**) On NATO Fellowship from Centre d3Etudes ~ ~ c~nfiguration ~ is expected to have a Of State a t about l ~ ~ i ~ ~ ~

.

de Saclay, BP no 2, 91- if-sur-~vette, France. 5.1 MeV. It was suggested by Ginocchio that the

and the theoretical fits. ^{6,. .*). IW(P}

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971654

C6-242 A. D. PANAGIOTOU, H. E. GOVE AND S. HARAR

levels O'(7.21 MeV), 2+(7.84 MeV) and 4+(10.57 MeV) weakly in the 4-particle transfer to 160. It is sug- may belong to this configuration. The two levels gested that they are the 6 + and 8+.

(0+, 2+) are very weakly seen in the 1 6 0 ( 6 ~ i , d)20Ne spectra, figure 2, and not at all in the 1 6 0 ( 7 ~ i , t)20Ne ^o,,,2,x

**rt9,s 768

640 ' 6 0 ( 6 ~ i . d ) 2 0 ~ e

512 384

=

_Z 2% ¹²⁸ Z I

U, f 7a8

=

0 640 512

384 256 128

320 €40 960 1280 1600 1920

CHANNEL NUMBER

FIG. 4. - a-particle spectra for the reaction 12C(12C, a).

FIG. 2. Deuteron spectra obtained in the reaction 160(6Li, d)zoNe.

I I 6 0 ( ? ~ i , t 1 2 0 ~ e

0: 30 MeV

+N 12"

CHANNEL NUMBER

FIG. 3. - Triton spectrum obtained in the reactlon 16O(7Li, t)zoNe.

one, figure 3, indicating that these levels have other than ( ~ d ) ~ configuration. In the l2C(I2C, a)20Ne reaction, however, the 2' level has a rather monotonic forward-peaking angular distribution, indicating an appreciable contribution from a direct 2 ⁽⁽ quartet ⁾⁾ addition to the [200] configuration. For the 4" member of the [220] configuration we suggest the 4' level at 9.03 MeV instead. This state is much more strongly populated in the 12C

+

12C reaction, figure 4, than in the I60('Li, t)20Ne one, indicating again other than ( ~ d ) ~ structure. The 6' (12.6 MeV) and 8 + (15.9 MeV) levels are similarly strongly popu- lated by transfering 8 particles to 12C and very

' O N C Rotational Bands and Classifications

FIG. 5. - E exc versus J(J

+

1) for the levels in 2oNe.

HIGH-SPIN HIGHLY-EXCITED STATES IN 2ONe C6-243

members of the [220] quartet configuration. In the 160(7Li, t)20Ne spectrum we observe a O + level at 8.6 MeV and a 2' a t 10.28 MeV [4], to be rather strongly excited. Also in the 160(6Li, d)20Ne spectrum the levels 2+(10.28 MeV) and 4'(12.77 MeV) are seen to be relatively strongly populated. Arima et a1 have suggested that the Of level of the [301] << quartet ⁾⁾ configuration is located a t about 8.8 MeV in 'ONe.

In the present experiment the transferring of a quartet

to the [300] 160 could form the [301] configuration in 2 0 ~ e . Therefore the levels O+, 2+ and 4' populated in this manner may be members of such quartet configuration.

Figure 5 is a plot of the energies of most of the known levels of 20Ne versus J(J

+

1). Lines are drawn between states believed to have same intrinsic struc- ture and classified into rotational bands.

References

[I] LITHERLAND (A. E.) and FERGUSON (J. A.), Can. J.

Phys., 1961, 39, 788.

[Z] HUNT (W. E.) et al., Phys. Rev., 1967, 160, 782.

[3] BERGMAN (C.) and HOBBIE (R. K.), Phys. Rev., 1971, 3, 1729.