Three-phonon States Research Articles

Vibrational levels in the 86-neutron nucleusGd150

The decay of 3.6-h $^{150}\mathrm{Tb}$ to levels in $^{150}\mathrm{Gd}$ has been studied by $\ensuremath{\gamma}$-ray and conversion-electron spectroscopy. A level scheme is proposed which accounts for all but 35 of the 256 $\ensuremath{\gamma}$ rays assigned to this decay. Most of the low-lying levels in $^{150}\mathrm{Gd}$ show a remarkably close correspondence with the predictions of the simple vibrator model. Possible candidates are observed for three-phonon quadrupole states and for the states coupling quadrupole and octupole phonons. The low-lying positive-parity levels can be adequately described by the phenomenological collective model of Gneuss and Greiner. The microscopic boson-expansion model of Kishimoto and Tamura, however, appears to predict $^{150}\mathrm{Gd}$ to be more transitional than the data imply. Systematics of the 86-neutron isotones show increased stability at 64 protons. This can be correlated with the filling of the ${g}_{\frac{7}{2}}$ and ${d}_{\frac{5}{2}}$ spherical proton orbitals.RADIOACTIVITY $^{150}\mathrm{Tb}$ [from $^{151}\mathrm{Eu}(^{3}\mathrm{He},4n)$], measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${E}_{\ensuremath{\beta}+}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\mathrm{ce}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$, and ${\ensuremath{\beta}}^{+}\ensuremath{-}\ensuremath{\gamma}$ coin; deduced $Q$, $log\mathrm{ft}$. $^{150}\mathrm{Gd}$ deduced levels, ICC, $J$, $\ensuremath{\pi}$. Enriched target, Ge(Li), and Si(Li) detectors.

Decay of 106mAg

Gamma rays and internal conversion electrons following the decay of 8.3 d 106m Ag were studied with Ge(Li) spectrometers and an orange type beta-ray spectrometer. Energies and intensities of some low energy gamma rays were measured precisely. Conversion coefficients for weak and high energy transitions were determined to estimate the multipolarities transitions. New gamma rays of 69, 70, 80, 83, 178, 434, 522, 950, 1051, 1077, 1168, 1178, 1349, 1419, 1909 and 2077 keV were observed. New levels are proposed from some of these gamma rays. Two three-phonon states are suggested on the basis of the observed gamma ray branching ratios to the low-lying two-phonon states.

The decay of 194Au to the levels of 194Pt

The γ-rays emitted in the decay of 194Au have been investigated by means of Ge(Li) detec tors. The energies and intensities of 93 γ-rays have been determined from the γ-ray singles spectrum. Two-parameter γ-γ coincidence experiments, with two Ge(Li) detectors, have been performed. The coincidence relations were used by the authors to construct a level scheme for 194Pt, consisting of 36 excited states. The ambiguities previously reported in the locations of several transitions have been removed, and several transitions have been placed in new positions. New levels at 1229.3, 1373.6, 2134.2, 2158.0, 2184.8 and 2287.3 keV have been postulated and five previously reported levels have been removed from the scheme. K-conversion coefficients, calculated from the γ-ray intensities of this work and the K-conversion electron intensities of Bergman and Bäckström, were used to determine the multipolarities of the transitions and the spin and parity assignments of the levels. Four levels are proposed as possible members of the quintet of three-phonon states.

Excitation of three-phonon vibrational states by inelastic α-particle scattering

The differential cross section for direct excitation by α-particle scattering of three-phonon vibrational states in spherical even nuclei has been calculated by means of the plane-wave Born approximation. A selection rule characterizing the scattering of zero spin particles by zero spin nuclei restricts the excitation to states of natural parity. Two corrections are introduced to prevent the nuclear volume change and, in the case of vibrations of odd multipolarity, the centre-of-mass shift of the target nucleus. When the interaction involves only a pure multipolarity λ, the former is found to influence the excitation of the states with I=0 or λ and the latter that of the 1 − state.

The decay of Au194

Abstract The decay of Au 194 was investigated by the use of high resolution spectrometers for the measurements of the conversion spectrum and a double lens spectrometer for coincidence measurements. By careful analysis of the conversion spectrum, which was recorded at a resolution of ≈0.2%, it was possible to identify more than 100 transitions in Pt 194 . The use of strong sources and a double counter operated in coincidence made possible the detection of lines of intensity only 10 −5 times that of the strongest line. Multipolarities could be found from K/L ratios for a few low energy transitions and some information could also be extracted from a comparison with results of previous gamma ray work. Energies of the strongest lines were measured absolutely by means of an iron free double focusing instrument, and further energy determinations were made relatively to these lines. The standard error of the measurements was frequently as low as 2 parts in 10 4 . A complete set of energy sums was computed in order to survey the possibilities of cascade-crossover combinations. The reliability of the numerical relationships was investigated statistically, and it was shown that a reasonably unique level scheme could be constructed on the basis of energies, although the positions of transitions remained to some extent ambiguous. The results of 79 coincidence experiments are reported, and when analyzed these data lead to a level scheme in agreement with the conclusions of the other approach. Furthermore, these experiments helped in deciding the location of transitions. Evidence for at least two 0 + states was found. The discovery of a level at 923 keV, probably of 4 + character, revealed a close analogy with the level scheme of Pt 192 . The interpretation of this level as a three-phonon state is in agreement with theory.