Identification of new transitions and mass assignments of levels in $^{143-153}$Pr

Abstract

Background : The previously reported levels assigned to 151,152,153 Pr have recently been called into question regarding their mass assignment. Purpose : Clarify the above questioned level assignments by measuring γ-transitions tagged with A and Z in an in-beam experiment in addition to the measurements from 252 Cf spontaneous fission (SF) and establish new spectroscopic information from N = 84 to N = 94 in the Pr isotopic chain. Methods : The isotopic chain 143−153 Pr has been studied from the spontaneous fission of 252 Cf by using Gammasphere and also from the measurement of the prompt γ-rays in coincidence with isotopically-identified fission fragments using VAMOS++ and EXOGAM at GANIL. The latter were produced using 238 U beams on a 9 Be target at energies around the Coulomb barrier. The γ-γ-γ-γ data from 252 Cf (SF) and those from the GANIL in-beam A-and Z-gated spectra were combined to unambiguously assign the various transitions and levels in 151,152,153 Pr and other isotopes. Results : A band of 3 new transitions added to the known level in 145 Pr, 9 new transitions in two new bands in 147 Pr, 6 new transitions in a new level scheme for 148 Pr, two new bands with 17 new transitions in 149 Pr and 2 new bands with 11 new transitions in 150 Pr were identified by using γ-γ-γ and γ-γ-γ-γ coincidences and A and Z gated γ-γ spectra. The transitions and levels previously assigned to 151,153 Pr have been confirmed by the (A,Z) gated spectra. Small changes have been made to their original level schemes. The transitions previously assigned to 152 Pr are now assigned to 151 Pr on the basis of the (A,Z) gated spectra. Two new bands with 20 new transitions in 152 Pr and one new band with 7 new transitions in 153 Pr are identified from the γ-γ-γ-γ coincidence spectra and the (A,Z) gated spectrum. In addition, new γ-rays are also reported in 143−146 Pr. Conclusions : New levels of 145,147−153 Pr have been established, reliable mass assignments of the levels in 151,152,153 Pr have been given in the present work and new transitions have been identified in 143−146 Pr showing the new avenues that are opened by combining the two experimental approaches.