Recoilless γ emission in ¹⁵⁶Gd and ¹⁵⁸Gd following neutron capture reactions

All the known nuclear-structure information on the A = 156 nuclides from ¹⁵⁶Nd through ¹⁵⁶Ta has been reviewed. These data are summarized and presented, together with adopted level schemes and properties based on an evaluation of them.

All the known nuclear-structure information on the A=156 nuclides from ¹⁵⁶Nd through ¹⁵⁶Ta has been reviewed. These data are summarized and presented, together with adopted level schemes and properties based on an evaluation of them.

The experimental results from the various reaction and decay studies leading to nuclides in the A=156 mass chain, and α decays from it, have been reviewed. These data are summarized and presented, together with adopted levels schemes and properties.

The 1964 version of Nuclear Data Sheets for A = 156 has been revised on the basis of experimental data received by August 15, 1974. Pertinent data received between August 15, 1974, and August 15, 1975, have been added in proof.

The A = 156 chain consists of ten nuclei (Sm through Lu). Three of these nuclei (Er through Yb) have been assigned since 1965. Level or decay schemes have been constructed for seven nuclei (Sm through Ho). Most data presented in the 1964 revision have not been retained; the references to some of these data may be found under Other Measurements.

The compilers have attempted to compare data with various models as an indication of where these models may be employed. Discrepancies in the data and other problems associated with the construction of the level schemes are pointed out in the Comments.

Experimental nuclear data for nuclides with mass 158 are presented.

All nuclei with Z between 62 and 72 with the exception of Lu (Z=71) have been reported for this mass number. Although gammas in ¹⁵⁸Eu ground-state decay have recently been studied with better accuracy, there is uncertainty regarding β-feeding of ¹⁵⁸Gd levels. The study of ¹⁵⁷Gd(n,γ) reaction with a crystal diffraction spectrometer has enabled the determination of ¹⁵⁸Gd levels with greater precision. However, there remain a large number of unassigned gamma transitions seen in (n,γ) reaction; also the conversion electron data from n-capture studies could not easily be correlated with other available data on ¹⁵⁸Gd. There is ambiguity regarding the Q⁺-value in (ε/β⁺)-decay of ¹⁵⁸Ho. It is also not clear which of the gammas seen in ¹⁵⁸Ho decay are due to the direct feeding of ¹⁵⁸Dy levels by the 27-m ^158mHo state.

Unless indicated otherwise, all energies given in the following pages are in MeV. Every effort has been made to include all data available prior to July 1, 1973. Some of the older data have been omitted or referenced under “other measurements.”