In-beam study of 70As

Abstract

Nuclear states of 70As were studied through the 69Ga(α, 3n), 60Ni(12C, np) and 63Cu(10B, 2np) reactions at various bombarding energies between 30 and 55 MeV. Excitation functions, γ-ray angular distributions, γ-γ coincidences, and γ-time distributions with respect to the beam bursts, were determined. Levels at 32.0, 167.0, 390.4, 485.4, 566.7, 869.1, 887.9, 898.7, 933.4, 1045.7, 1675.9, 1752.0, 1809.2, and tentatively at 2030 keV, were observed. All levels below 900 keV can be identified with levels seen with the (p, nγ) reaction. Tentative spin assignments extend up to J = 9. Two previously reported isomers are confirmed. The present measurements yield 3.3±0.7 and 4.4±0.1 ns for the 485.4 and 887.9 keV states, respectively. No collective features, as in the lighter isotone 68Ga, were found. The levels below 1 MeV are likely to be described by simple shell-model configurations. The spacing of the proposed J = (4), (5), and (6) levels is analogous to that in 72As and 74As