Physics & Astronomy Faculty Work


Coexisting single ­particle and collective excitations in 70As

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​Physical Review C

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High-spin states in 70As were studied using the 55Mn(18O,3n) fusion-evaporation reaction at a beam energy of 50 MeV. Prompt γ−γ coincidences were measured using the Florida State University Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. A reinvestigation of the known level scheme resulted in the addition of 32 new transitions and the rearrangement of 10 others. The high-spin decay pattern of yrast negative-parity states was modified and enhanced extensively. Spins were assigned based on directional correlation of oriented nuclei ratios. Lifetimes of seven excited states were measured using the Doppler-shift attenuation method. The B(E2) rates inferred from the lifetimes of states in the yrast positive-parity band imply substantial collectivity, in agreement with the results of previous studies. Substantial signature splitting and large alternations in the B(M1) strengths were observed in this band as well, supporting the interpretation of an aligned πg9/2⊗νg9/2 intrinsic configuration for this structure beginning at the lowest 9+ state. Large-scale shell-model calculations performed for 70As reproduce the relative energy differences between adjacent levels and the B(M1) rates in the yrast positive-parity band rather well, but underestimate the B(E2) strengths. The g9/2 orbital occupancies for the lowest 9+ state predicted by the shell-model calculations provide additional evidence of a stretched πg9/2⊗νg9/2 configuration for this state.



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