First observation of low-lying excited states in 232Pa

Complete text of publication follows. The actinide region is very rich in interesting nuclear phenomena (fission, super- and hyperdeformed shapes, cluster decay, superheavy elements etc.) and contains important isotopes (Th, Pa, U) also for energy production (fission). However, the spectroscopic information for the low-lying excited states are scarce. The well known spectroscopic tools like one particle transfer reactions could not be used because of the lack of suitable targets. With respect to the hyperdeformation, the double-odd 232Pa nucleus is of great interest. The level scheme of this isotope is completely unknown except for the ground-state level (Igsπ = 2-), although it could be important in fixing the proton-neutron residual interaction part of the shell model description in this mass region. The aim of this work was to study the low-lying excited states in 232Pa using (d,p) reaction on the radioactive 231Pa target. The experiment was performed at the Munich Tandem accelerator. The deuteron beam energy was Ed = 12 MeV. A 80 μg/cm2 thick 231Pa target on a 20 μg/cm2 thin carbon backing was used. The kinetic energy of the proton ejectiles was analysed with a Q3D magnetic spectrometer placed at ΘL = 140 deg relative to the incident beam, covering a solid angle of 10 msr. The position of the analyzed particles in the focal plane was measured with a position-sensitive light ion focal plane detector with individual cathode strip readout of 890 mm active length. The spectrum was analyzed with a fitting program GASPAN. The energy and the relative differential cross section were determined for 35 new excited states below 900 keV. A typical part of the fit is shown in Fig. 1. The spin and parity assignment is still the subject of further measurements of the angular distribution. (author)