Levels and transitions in136Ba

Abstract

Excited states of 136Ba are studied in the beta decay of 136Cs. The gamma spectrum is measured with high-resolution and coincidence techniques. Several new transitions are suggested to be connected with two recently reported levels. Gamma-gamma directional correlations are performed in an attempt to determine the characteristics of these levels, and in order to determine mixing ratios. The lifetime of the 2207.5 keV state is remeasured, and the lifetime of the 2140.5 keV state is measured for the first time.The level scheme of larBa has been investigated in the beta decay of 136Cs [1][2][3][4][5][6][7][8] and electron capture of la6La [10,11], and in neutron capture [12][13][14][15] and inelastic scattering [16]. The nucleus la6Ba may be regarded as transitional in the sense that the low-lying excitations have been described in terms of a quasi-rotational band [17], and as phonon states [11]. The first excited states, with I~=2 +, 2 +, 0 +, and 4 +, occur at 818.6, 1551.1, 1579.0, and 1866.5 keV, respectively. In an energy region just above the 4 + level many states appear. These states are partly deexcited by highly retarded E1 transitions. In the shell-model picture they are interpreted as two-particle (hole) configurations. A further clarification of the level scheme of this transitional nucleus should be important for elucidating the interaction between the quasi-particles, and the nature of the collective excitations.The decay of ~36Cs has been studied in this work. Due to the spin of the parent, I~= 5 +, preferentially states of fairly high spins are populated in this decay.The 136Cs activity was produced in a (d, e) reaction by irradiating enriched (99.8~) laSBa, as nitrate, with 25 MeV deutrons at IKO, Amsterdam. A 36 cm 3 Ge (Li) detector was employed in the measurements of the gamma spectrum. Several measurements were performed during 5 half-lives of the source, in order to show that all transitions are charactensed by the decay constant of ~ 3 6Cs. The result of the intensity measurements is presented in Table 1, together with the data by Fr~ina et al. [8].The Ge (Li) detector was used in coincidence with a NaI (T1) detector in order to testify that the new transitions belong to ~a6Ba, and in order to place them in the level scheme. The six weak transitions found in this 1 Z. Physik, Bd. 260

Spectroscopy of states in $^{136}\rm{Ba}$ using the $^{138}\rm{Ba}(p,t)$ reaction

“…E x = 2356.3 keV: This is a well-known 4 + state [31] observed in (n, γ), (n, n γ) and 136 Cs β-decay studies [47,49,51]. The spin and parity of the state was ascertained from both γ-ray angular distribution [47] and directional correlation [51] measurements, which showed strong E2 components in the 4 + → 2 + → 0 + transitions. However our analysis shows that the L = 5 transfer is more consistent with the measured distribution.…”

“…This is not surprising as the state is fed via a Gamow-Teller transition in 136 Cs β − decay, with a measured log f t value of around 5.9 [16]. This indicates a (d 3/2 ) n → (d 5/2 ) p transformation [51], with a dominant (g 7/2 , d 5/2 ) proton configuration for the state. Therefore, the 6 + 1 state is not expected to be strongly populated in 138 Ba(p, t).…”