Study of the excited levels of 233Pa by the 237Np alpha decay

The excited levels in 233Pa following the 237Np alpha decay have been studied by performing different experiences to complete available data and supply new information. Thus, two direct alpha spectrum measurements, one alpfa-gamma bidimensional coincidence experiment, three gamma-gamma and gamma-X ray coincidences and some other measurements of the gamma spectrum, direct and coincident with alpha particles have been made. These last experiences have allowed to obviate usual radiochemical separation methods, the 233Pa radioactive descendent interferences being eliminated by means of the coincidence technics. As a result, a primary decay scheme has been elaborated, including 15 new gamma transitions and two new levels, not observed in the most recent works. Using precedent data on 233Th beta decay and nuclear reactions, the 233Pa excited states have been classified into 11 rotation and vibration bands, employing the collective model. (author)