Spin States of Neutron Resonances in Gadolinium and Europium

The spin states associated with several neutron resonances in gadolinium and europium have been assigned by observing the transmission of polarized neutrons through polarized targets. For the levels in Gd¹⁵⁵ at 0.0268, 2.01, 2.57, and 6.30 eV, the spin states were found to be J=2, 1, 2, and 2, respectively, and for the 0.0314-eV level in Gd¹⁵⁷, $J=2$. For the resonances in Eu¹⁵¹ at 0.32, 0.46, 1.06, and 3.37 eV, the spin states were found to be J=3, 3, 3, and 2, respectively, and for the negative level, $J=3$. For the 2.46-eV resonance in Eu¹⁵³, $J=3$. There appears to be no correlation between these measured spin states and other resonance parameters. The magnitude and direction of the observed effects are discussed in terms of the effective magnetic field at the nucleus and the magnetic properties of the metals at low temperature.