Nuclear Physics Al59(1970) 249-256; @ North-HoNand Publishing Co., Amsterdam Not to be reproduced by photoprint or microfilm without written permission from the publisher zyxwvutsrqpo ODD PARITY STATES IN 23sPu B. BENGTSON, J. JENSEN, M. MOSZYt&KI? and H. L. NIELSEN Institute of Physics, University of Aarhas, Denmark Received 24 June 1970 Abstract: The decay of 2.1 d 238Np was investigated by means of singles and coincidence spectromelry with Ge(Li) counters and a six-gap orange beta-spectrometer. Fast lifetime techniques with Ge(Li) detectors were used. New 23sPu levels were established at 1082.6 keV (K, I” = 4.4-i t+ = 8.5*0.5 ns) and 1202.4(3, 3-), they are interpreted as the 2 = 0 and z = 1 doublet of the [7433$-, [631]$+ two-neutron configuration. Other odd parity levels were established at 661.4(0, 3-), 962.7(1, I-), 985.5(1, 2-) and 968(2, 2-). E RADIOACTlVITY 238Np(from ‘s’Np(n,y)]; measured E,,, 1y yy-, w-coin., y//-, &delay; deduced log zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML ft. ‘s8Pu deduced levels, J, n, T+. zyxwvutsrqponmlkjihgfe 1. Introduction In the even nucleus 238Pu one expects a two-quasiparticle state with K” = 4- and configuration (in terms of Nilsson quantum numbers) n [743]$- + n[63 1It_’ to occur as a particularly low excitation since the neutron states involved are ground states in the odd-A neighbours 237Pu and 239Pu, respectively. The calculations of Soloviev and Siklos ‘) predict this 4- state to occur at 0.9 MeV, lower in energy than any other two-quasiparticle state in 238Pu. Previous experiments, for which we refer to ref. ‘) have established many levels in 238Pu around 1 MeV but there is no evidence in the literature of a 4- state. The present work was undertaken to search for such state in the decay of 2.1 d 238Np. Since a 4- state is expected to possess a measurable half-life, the experimental investigation was based on delayed-coincidence techniques combined with high-resolution Ge(Li) y-ray detectors. 2. Experimental technique Sources of 2.1 d 238Np were prepared by irradiation of 10 pg samples of 237Np in the DR3 reactor at Riser. Neptunium was isolated chemically by means of anion- exchange in HCl solutions. Singles y-ray spectra were taken with a 35 cm3 true coaxial Ortec Ge(Li) detector, and with a 0.25 cm3 Ortec Ge(Li) X-ray spectrometer. Electron-gamma coincidences were performed by means of the combination of a six-gap orange beta-spectrom- + On leave from Institute of Nuclear Research, Swierk near Warsaw, Poland. 249