The decay of 1.4 min¹⁷³Er

Abstract

A 1.4 ± 0.1 min activity which is assigned to β⁻-decay of ¹⁷³₆₈ Er has been produced with 14–15 MeV neutrons through the reaction¹⁷⁶Yb(n, α)¹⁷³Er. Its decay has been studied with Ge(Li) detectors and several (γ)(γ) as well as (γ)(β) coincidence arrangements. Eight gamma rays with energies 94.2, 116.14, 118.6, 122.40, 192.8, 199.2, 800.8 and 895.2 keV were assigned to the decay of¹⁷³Er. The proposed level scheme of the daughter nuclide ¹⁷³₆₉ Tm contains levels at 0, 2.5, 118.6, 124.9, 317.7, 411.9 and 1212.8 keV. The 317.7 keV level is an isomeric state with a measured half-life of 10±3 μs. This 10 μs isomer and the 411.9 keV level are thought to be the band head and 9/2⁻ rotational member of 7/2⁻ [523] Nilsson state, respectively. The levels at 0, 2.5, 118.6 and 124.9 keV are interpreted as 1/2⁺, 3/2⁺, 5/2⁺ and 7/2⁺ members of the 1/2⁺ [411] band and the level at 1212.8 keV as the 9/2⁻ [514] Nilsson state. Some systematic considerations and theoretical transition probability calculations are also included.