Excited States In The Highly Deformed Proton Emitter 131Eu

Abstract

The newly commissioned JUROGAM 3 γ-ray spectrometer was used in conjunction with the MARA recoil separator to establish excited states in the proton emitting nucleus ¹³¹Eu, which is predicted to possess one of the highest quadrupole deformations in the 130 ≤ A ≤ 140 region. By identifying the rotational band structures in this nucleus, deformation parameters can be established that provide crucial constraints on theoretical models of deformed proton emitters. Fine structure has previously been observed in the proton emission from ¹³¹Eu. The sensitivity of the fine structure to the wavefunctions of states in the parent and daughter nuclides generated significant theoretical interest in this nuclide allowing a 3/2+ spin parity assignment to be made for the ground state. The composition of the wavefunctions are highly sensitive to dynamic effects, therefore it would be particularly informative to study the excited states built upon the 3/2+ state and other low-lying Nilsson bandheads. Proton radioactivity from ¹³¹Eu has been remeasured with a proton energy of 952(5) keV for the ground-state decay to the ground state in the ¹³⁰Sm daughter and a proton energy of 828(6) keV for the fine structure transition from the ground state in ¹³¹Eu to the 2+ excited state in the ¹³⁰Sm daughter. The 2+ to 0+ transition in ¹³⁰Sm was also measured directly for the first time with an energy of 125(1) keV. The ¹³¹Eu nucleus was produced with a cross section of 140(30) nb with a 23(5) % fine structure branching ratio. The half-life was measured to be 17.6(5) ms. In-beam data from this study was highly fruitful and through gamma-ray correlations it was possible to build rotational band(s). The obtained band(s) in this study cannot firmly be assigned, however comparison to the ¹⁴¹Ho structure suggests that the band is based on 7/2[523] Nilsson state. No clear evidence for existence of any sort of isomeric decay feeding the ground state could be identified. Keywords: Nuclear structure, decay spectroscopy, proton emission, in-beam spectroscopy, neutron-deficient nuclei