Picosecond lifetime measurements in 109Cd and 110Cd

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176 S. Harissopulos et al. / Nuclear Physics A 683 (2001) 157–181 Fig. 12. Experimental decay curve of the 21/2 (+) excited state of level sequence “7” in 109 Cd. The data points are the intensity of the Doppler unshifted component of the 1045 keV γ -transition which deexcites the level considered. The solid curve is obtained by fitting a single exponential function to the data points which yields a mean lifetime of 1.82(28) ns. feature of the decay curves measured for the members of this level sequence is that they all have the same effective lifetime, i.e. τ e ≈ 9(1) ps. This may suggest that the mean lifetimes of the levels considered are rather short, i.e. τ
S. Harissopulos et al. / Nuclear Physics A 683 (2001) 157–181 177 5. Discussion The B(E2) values determined in the present work for the lowest E2 yrast band γ -transitions of 110 Cd are given in Table 2. The B(E2) values determined in the present work for the 2 + 1 → 0+ 1 and 4+ 1 → 2+ 1 γ -transitions are in rather good agreement with those reported in Ref. [29]. The latter B(E2) values have been determined in previous Coulomb excitation measurements. In addition, the B(E2) values derived in our work for the 2 + 1 → 0+ 1 and 4+ 1 → 2+ 1 γ -transitions are in rather good agreement with those reported in Refs. [28] and [30], respectively. According to the transition probabilities obtained in 110 Cd, an increase of the B(E2) values occurs up to the 8 + 2 state at E x = 3275 keV. Above this level one distinguishes between a “fast” and a “slow” pathway (see Fig. 5). The former proceeds via the 802 keV γ -transition, through which the 10 + 2 level is deexcited. For this γ -transition Piiparinen et al. [28] as well as Lobach et al. [30] have reported high B(E2) values of 74(24) W.u. and 60.4(186) W.u., respectively. In the present work only a lower limit of B(E2; 802 keV)>16 W.u could be determined. The “slow” pathway proceeds via the 335 keV γ -ray deexciting the 10 + 1 state. For the 335 keV γ -ray a B(E2; 335 keV) = 6.6(4) W.u. has been obtained in the present work. Above the 10 + 1 state the collectivity “recovers”: a high transition probability of B(E2) = 41(2) W.u has been here determined for the 12 + 1 → 10+ 1 γ -transition (E γ = 561 keV). An interesting feature in the level scheme of 110 Cd, is the existence of three closelying 8 + states. These states are shown in Fig. 5, in which the respective excitation level energies are given in parenthesis. According to [7,8,28] the lowest lying 8 + state at E x = 3187 keV is fed by the 10 + stateviaa424keVγ -ray and is further deexcited to 6 + 1 state through a 707 keV γ -transition. The B(E2) value obtained here for the 424 keV populating γ -transition is rather low: B(E2; 424 keV) = 0.05(2) W.u. This value clearly indicates a significant difference between the configurations of the 8 + 1 at 10+ 1 states. On the other hand the high transition rate (B(E2; 171 keV) = 45(5) W.u) determined here for the 171 keV γ -ray deexciting the 10 + 1 state and feeding into the 8+ 3 level at E x = 3440 keV is a strong argument for assigning the same character in both states. Unfortunately, due to statistics and the fact that the decay curve measured in the present work for the 960 keV γ -ray (8 + 3 → 6+ 1 ) is “obscured” by the strong slow feeding from the 10+ 1 state, it was not possible to extract a mean lifetime for the 8 + 3 level and further obtain the B(E2) value of the 8 + 3 → 6+ 1 γ -transition. However, Lobach et al. [30] have reported for this γ -ray a B(E2) value of 9.8(42) W.u. which suggests different configurations for the 8 + 3 and 6+ 1 states. In Fig. 13(i) the relative B(E2) values measured here for 110 Cd are compared with the respective ratios predicted by the U(5)-limit of IBM-1. Hence, in Fig. 13(i), the ratios [ B(E2; I → I − 2) R = R exp. B(E2; 2 + 1 = → 0+ 1 ]exp. [ ) R U(5) B(E2; I → I − 2) (7) B(E2; 2 + 1 → 0+ 1 ) ]U(5)
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Page 7 and 8: Fig. 3. Experimental decay curves Q
Page 11 and 12: Table 2 Mean lifetimes τ and B(E2)
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Picosecond lifetime measurements in 109Cd and 110Cd

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