Studies on the long-lived activities of europium

Abstract

Long-lived activities of europium, Eu¹⁵² (13y) and Eu¹⁵⁴ (16y), were studied by a coincidence scintillation spectrometer. The measured gamma ray energies (keV) and their relative intensities are 80±4 (0.52), 124±4 (1.85), 244±7 (1.00), 340±10 (2.16), 410±20 (0.15), 710±25 (0.34), 770±22 (1.27), 870±30 (0.57). 970±20 (1.93), 1090±21 (1.88), 1260±40 (0.5), 1410±25 (1.99). X-gamma and gamma-gamma coincidence experiments were carried out by employing pulse-height selection; beta-gamma coincidence were recorded by using an anthracene crystal spectrometer. Decay schemes for the two isotopes are proposed on the basis of our experimental results. The first two excited states of Sm¹⁵² reached by the capture decay of Eu¹⁵² at 121 and 365 keV are identified as rotational levels belonging to the ground state configuration; higher excited states in Sm¹⁵² (N = 90) were also reached by capture decay of Eu¹⁵². On the other hand the first two excited states of Gd¹⁵² (N = 88) reached by β^--decay of Eu¹⁵² at 340 and 750 keV are probably vibrational in origin. The ground state spin of Eu¹⁵² is assigned as 4. The newly found gamma ray of energy 80 keV is identified as the one arising from deexcitation of the first rotational level of Sm¹⁵⁴, a state which has also been observed in Coulomb excitation experiments. Decay schemes are discussed in the light of the unified nuclear model.