Picosecond lifetime measurements in 109Cd and 110Cd

180 S. Harissopulos et al. / Nuclear Physics A 683 (2001) 157–181
The reduced transition probabilities determined in 109 Cd are rather large. Especially
in level sequence “4” it was found that B(E2; 15/2 − → 11/2 − ) = 47(3) W.u. In
107 Cd, Häusser et al. [13] have obtained B(E2; 15/2 − → 11/2 − ) = 32(2) W.u. This is
indeed a drastic change when considering that the respective γ -transitions differ only by
7 keV. In the weak coupling scheme, it is expected that B(E2; 15/2 − → 11/2 − )109 Cd ≈
B(E2; 2 + → 0 + )110 Cd , whereas in the rotational aligned coupling the B(E2; 15/2− →
11/2 − )109 Cd value is slightly larger. In our case B(E2; 15/2− → 11/2 − )109 Cd ≈ 2 ·
B(E2; 2 + → 0 + )110 Cd . Hence, our result deviates significantly from the values expected.
An interesting feature of level sequences “2” and “3” in 109 Cd, is that the B(E2) values
deduced from the mean lifetimes of the respective depopulating E2 γ -transitions do not
change significantly with increasing spin. According to the B(E2) values obtained for the
21/2 + → 17/2 + ,23/2 + → 19/2 + ,25/2 + → 21/2 + , and 27/2 + → 23/2 + γ -transitions
the collectivity in these level sequences is almost constant (≈ 50 W.u).
6. Conclusions
In the present work the mean lifetimes of 9 excited states in 109 Cd have been determined
for the first time. The corresponding B(E2) values are rather large.
In 110 Cd, the mean lifetimes of the lowest 6 yrast band members have been measured.
Hence, it was possible to follow the evolution of the B(E2) values along the yrast line of
110 Cd. Based on the relative B(E2) values determined here and in [28] one could claim that
the 110 Cd is one of the best examples of nuclei resembling the U(5) symmetry of IBM-1.
This has been also shown by Kern et al. [2] in terms of the energies of the excited states in
110 Cd.
The comparison of all experimental B(E2) values reported so far for the E2 γ -transitions
deexciting the lowest lying collective states in the even even Cd nuclei, are in a remarkably
good agreement with the respective predictions of the U(5) limit of IBM-1. Certainly, it
would be very interesting to determine more B(E2) values along the yrast lines of these
nuclei in order to check further the U(5) character of these isotopes.
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