Search for a shape isomer in ²³³Th

A search for a shape isomer in ²³³ 233 Th via delayed γ γ decay was performed using the Heidelberg–Darmstadt Crystal Ball spectrometer together with a E Δ E – E telescope for light charged particle identification. Excited states in ²³³ 233 Th were populated through the ²³² 232 Th( d , p ) reaction. The search for isomeric γ γ decay was based on a total-energy reconstruction method: prompt energy deficits EMiss E Miss indicated possible long-lived isomeric states. Corresponding delayed summed energies ESumdel E del Sum were recorded with the Crystal Ball. A two-dimensional analysis of EMiss E Miss versus ESumdel E del Sum was carried out for various prompt and delayed multiplicities and for delayed time intervals up to 200 ns within the excitation-energy range Eˣ = 3 E x = 3 –7 MeV. No evidence of isomeric γ γ decay was observed. The branching ratio for the population of a potential shape isomer in the second minimum of ²³³ 233 Th relative to the first minimum is constrained to < 10⁻⁶ < 10 - 6 , for isomeric states with energies Eˣ = 2 E x = 2 <