LIFETIME MEASUREMENTS IN SD-SHELL NUCLEI .I. MEAN LIVES OF 38AR LEVELS

The 41K(p,αγ) and 35CI(α, pγ) reactions were used to populate levels in 38Ar. The mean lives of the lowest six excited states in 38Ar were measured with the Doppler shift attenuation method. Gamma rays were detected at 90°, in coincidence with particles observed at angles θ = 100° and -100° or 110° and -110°. The 38Ar* ions slowed down in thick carbon backings, the stopping power of which is known experimentally. Mean lives of τm = 540 ± 65, 7000 ± 4000, 75 ± 30, 46 ± 18, ≦ 1500 ± 330 and 25 ± 25 fs were found for the levels at Ex = 2.17, 3.38, 3.81, 3.94, 4.48 and 4.57, respectively. The relatively fast decay of the second excited state indicates that positive parity states in 38Ar are only well described if (ds)-4(fp)2 shell-model configurations are taken into account. © 1969.