Volume 26B, number 3 PHYSICS LETTERS 8 January 1968

A DETERMINATION OF THE GYROMAGNETIC RATIOS OF I6IDy FROM BRANCHING-RATIO MEASUREMENTS

G. B. HAGEMANN and A. TVETER * The Niels Bohr Institute, University of Copenhagen, Denmark

Received 4 December 1967

The ground-state band up to spiny of 16IDy has been studied by Coulomb excitation with 46 MeV oxygen ions. Gamma rays from thin 16IDy isotope separated targets (0.1 mgQm2) were observed in coincidence with backscattered ions. From the observed branching ratios go = 0.11 -I- 0.02 and gK = -0.30 i 0.02 were derived for the gyromagnetic ratios.

In an earlier measurement of branching ratios in a series of deformed odd-A nuclei [l], includ- ing 161 Dy (enriched to 900/,), y rays from the ro- tational states populated by Coulomb excitation with l6 0 ions were observed in a Ge(Li) detec- tor .

In the present experiment a highly enriched (99.9%) 16IDy target was used. The y rays in co-

K,P 5 11+ 2 . 2

5 11+ r. 2

incidence with 46 MeV 160 ions backscattered into a ring counter were detected in a 3 cm3 Ge(Li) detector. The detector was calibrated in situ by the use of 182Ta and 169yb sources for which the y intensities are known to high accur-

acy PI- The condition of the y rays being in coinci-

* Present address: University of Oslo, Norway.

keV

268.5

183.8

100.5

43.8

0

16’ Dy

Fig. 1.

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Volume 26B, number 3 PHYSICS LETTERS 8 January 1968

Table 1

Spin transition IY

l/62 Itotal cross section mb/sr

exp c, theory

9 I-5 100.0 l 0.5 22.9 -1-1.7 84* I 2 19.7 * 4.2 21.3

9 -++ 2 56.7 + 0.4 21.5 + 3.2 1260 + 210 b)

‘i! y_; 141.0 + 0.6 41.4 l 1.5 74* 3 6.9 i 0.9 5.9 9-Q 83.3 * 0.5 66 f4a) 15.1 * 1.7 340 l 40

ia $3-9 168.0 f 1.0 22.5 + 2.5 32* 4 2 2.0 * 0.2 2.2

v-$i 84.5 * 0.5 14 +4 a) 20.7 zt 3.1 68.0 f 1.3

a) The 84 keV peak has been separated in the two components, with the assumption that (gK-gR)2/$ is constant throughout the band.

b, The intensity is estimated on the basis ofIy(lOO keV) and (gK-gR)2/Qi. C) The measured relative cross sections are normalized to the theoretical values by minimizing the weighted average

deviation.

dence with backscattered ions enhances the mul-

tiple Coulomb excitation process. On the basis

of the observed coincidence y-ray spectrum the Z = y and y states were placed in the level scheme as shown in fig. 1. This level structure is confirmed by the 16ODy(d, p) l6lDy and the 162Dy(d, t)161Dy reactions recently studied [3].

The spectrum is thus complicated by the two y rays at about 84 keV; the compone

% & t in ensities

were found by assuming that (gK-gR) /Q. is a constant for the band.

For the excited state with spin Z, for which the branching ratio has been measured, the quan- tity (gK-gR) has been calculated from the rotatio- nal model as described in ref. 1. With the cross- over-to-cascade intensity ratio “y = 0.63 f 0.07, we get ]gK-gRly = 0.41 f 0.03, and using the ground state magnetic moment of 16l~y of ref. 4 we derive

gR = 0.11 f 0.02 and gK = -0.30 f 0.02 .

The values published previously in ref. 1 are too large due to an overestimation of the 84 keV y -+ f intensity which was complicated further - more by an 81 keV component due to a ‘7.8% ad- mixture of 162~y in the target.

The present values of gK and gR are close to recent theoretical calculations by Prior et al. [5] who have calculated gK = -0.26 and gR = 0.04, and by Hrynkiewicz and Ozaga [6] who have pre- dicted go = 0.09. Although the experimental value is slightly larger than the theoretical value, it still supports the particularly low theoretical go value of lslDy.

From the observed relative in assumption of a constant (gK-& B a

ens’ties and the /QO for the

ground-state band, the total transition intensities

have been evaluated by means of the theoretical conversion coefficients of Hager and Seltzer [‘I]. These values are given in table 1, together with the values of 1/62 used. The experimentally de- termined cross sections are, within errors, in agreement with those calculated by means of the theory of multiple Coulomb excitation [8] (cf. table 1).

The authors are indebted to the group at the Isotope Separator, University of Aarhus, for the preparation of targets, and to Professor F. Boehm for his interest in the experiment. A. T. acknowledges a fellowship from the Royal Nor- wegian Council for Technical and Scientific Re- search.

References 1. F.Boehm et al., Phys. Letters 22 (1966) 627, and

Erratum, Phys. Letters 23 (1966) 491. 2. W. F. Edwards et al., Nucl. Phys. 63 (1965) 97:

P. Alexander and F. Boehm, Nucl. Phys. 46 (1963) 108. 3. T. Grotdal, K. Nybe, T. Thorsteinson and B. Elbek,

to be published. 4. I. Lindgren, in Perturbed angular correlations, eds.

E. Karlsson, E. Matthias and K. Siegbahn, (North- Holland Publ. Co., Amsterdam, 1964).

5. 0. Prior, F. Boehm and S. G. Nilsson, to be pub- lished.

6. A. Z. Hrynkiewicz and S. Ogaza, Institute of Nuclear Physics, Krakov, Poland, Report No. 466/‘PL, 1966.

‘7. R. S. Hager and E. C. Seltzer, Internal conversion tables, CALT-63-60, AEC Research and Develop- ment Report, 1967.

8. K. Alder and A. Winther, Nucl. Phys. 37 (1962) 194, and Computer Programme: A. Winther and J. de Boer, Technical Report, November 18, 1965, available from the California Institute of Technology and Rutgers, The State University.

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