Messung des g_R-Faktors des 2+-Rotationsniveaus von Dy¹⁶⁰ nach der Spinrotationsmethode und Bestimmung der Multipolmischungen mehrerer γ-Übergänge im Zerfall des Tb¹⁶⁰

Abstract

A differential measurement of the spin rotation of Dy¹⁶⁰ in the 2+ rotational state was performed by using liquid sources of TbCl₃ solved in 3M HCl and applying an external magnetic field of 33 500 Gauss. No change of the Larmor precession frequency could be detected within the first 10·10⁻⁹ s. It is concluded that the ground state of the electronic shell of Dy⁺⁺⁺ is reached in 6·10⁻¹⁰ s after theβ-decay of Tb¹⁶⁰. The valueg _R=+0.364±0.011 was derived using 〈r⁻³〉_eff=8.92 a. u. for the 4f-shell of Dy⁺⁺⁺. A comparison with the result ofCohen who studied the Mössbauer-effect in Fe₂Dy shows that the value of 〈r⁻³〉_eff must be 10% larger in this compound.

A measurement of the effective magnetic field at the position of the nucleus in a source of terbium metal was performed for different temperatures. It revealed a temperature dependence which is very similar to the paramagnetic susceptibility χ(T). We observed a strong attenuation ofγ γ-angular correlations in the 2+ rotational state. For liquid sources of TbCl₃ solved in 3M HCl the following attenuation parameters were measured:

$$\begin{gathered} \lambda _2 = (0.122 \pm 0.013) \cdot 10^9 {\text{s}}^{ - {\text{1}}} , \hfill \\ \lambda _4 = (0.235 \pm 0.024) \cdot 10^9 {\text{s}}^{ - {\text{1}}} . \hfill \\ \end{gathered}$$

The ratioλ ₄/λ ₂ deviates from the value which is expected for the attenuation by internal fields of the 4f-electronic shell. Possible reasons are discussed.

We derived the following multipole mixtures ofγ-transitions in the decay of Tb¹⁶⁰:

$$\begin{gathered} \delta (879 {\text{keV) = + 17}}{\text{.7}}_{ - {\text{2}}{\text{.8}}}^{{\text{ + 5}}{\text{.2}}} (M1 + E2) \hfill \\ \delta (299 {\text{keV) = }} - 0.029 \pm 0.005 (E1 + M2) \hfill \\ \delta (329 {\text{keV) = }} - 0.023 \pm 0.007 (E1 + M2). \hfill \\ \end{gathered}$$

The half life of the 2+ rotational state was redetermined as

$$T_{\tfrac{1}{2}} = (1.99 \pm 0.04) \cdot 10^{ - 9} {\text{s}}{\text{.}}$$