E. Bodenstedt

A dilution refrigerator for low temperature nuclear orientation experiments on line to an isotope separator

A system for low temperature nuclear orientation studies is presented where the sample can be prepared by in situ implantation of ions from an isotope separator into a host lattice at temperatures <0.5 K. The special construction of the cryostat necessary for this purpose as well as the beam line from the isotope separator to the cryostat are described in detail. A description of the data acquisition arrangement appropriate to the experiments planned is given. The cooling characteristics of the refrigerator under different operating conditions are discussed. A first successful nuclear magnetic resonance experiment on oriented 197mHg implanted in situ at T<0.5 K is reported.

Measurement of the electric quadrupole moment of the 482 keV state of 181Ta by the time differential perturbed angular correlation technique

Abstract The electric quadrupole interaction of the 482 keV state of 181Ta in an environment of metallic rhenium has been investigated by time differential angular correlation measurements. For the field gradient calibration a recent observation1, 2) of the quadrupole splitting of the 6.3 keV line of 181Tain the same environment has been used. Adopting the quadrupole moment of the ground state which was derived from muonic X-ray data 3) we obtain Q 5 2 (482 keV ) = 2.51 ± 0.15 b . A comparison of the intrinsic quadrupole moment Q0 with that of the ground state revealed that the excited state is slightly less deformed: Q 0 ( 5 2 + )/Q 0 ( 7 2 + ) = 0.936 ± 0.014 . A measurement of the temperature dependence between liquid nitrogen and room temperature showed that the electric quadrupole interaction remains essentially constant.

Measurement of lifetimes up to one second of isometric nuclear states populated in the decay of radioactive sources

Abstract We have measured the half-life of the 1.1s isomeric state of 177Hf populated in the decay of 155d 177mLu by the coincidence technique. This measurement revealed some interesting new phenomena of the theory of accidental coincidences. They are described together with the experimental setup which was developed for this investigation.

Observation of dipole-octupole mixture in the gamma-decay of the 1174 keV isomeric state of Yb172 and its magnetic moment

Abstract Measurements of γγ-angular correlations in the decay of Lu172 revealed that the 1095 keV γ-transition has the unusual multipole mixture of 95% dipole radiation with 5% octupole radiation. This transition is strongly retarded by the K selection rule. We redetermined the half life of the 1174 keV state as T 1 2 = 8.4±0.3 ns . The g factor of the state has been measured by applying the spin rotation method. The result g = +0.214±0.014 was compared with the predictions of the Nilsson model. The best fit was obtained for the two-neutron configuration [514↓–521↓]. The g factor measurement as well as additional γγ-angular correlation measurements favour the assignment of a positive parity to the isomeric state. Angular correlation measurements of the 901 keV-1095 keV cascade and the 811 keV-91 keV-1095 keV triple cascade agree with the assignment of the spin I = 4 to the 2075 keV state; only the spin I = 2 cannot be excluded. The angular correlations are slightly attenuated by interactions with the strong fields of the unfilled 4f electronic shell. We derived the spin relaxation time of the 4f shell as τJ = (2.0±0.5) · 10−13s. This result was obtained for liquid sourced of LuCl3 solved in dilute hydrochloric acid.

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

AbstractA 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 valuegR=+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:

The quadrupole moments of the 5− states in 116Sn, 118Sn and 120Sn

\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}

Magnetic properties of the [624]92 rotational band in 177Hf

The ratioλ4/λ2 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: