Analogous negative parity spectra of125Xe and127Xe

Abstract

Abstract. The low spin states of the nucleus 127Xe have been investigated with the (c~,2n) reaction by means of in-beam-7-spectroscopy, using the osiRis-cube-spectrometer at the FN TANDEM accelerator facility of the University of Cologne. In the negative parity system, four excited states for each of the spins 11/2-..15/2-and two 5/2-..9/2--states could be established at excitation energies up to ~ 1MeV above the Yrast line. With this new data, we are able to compare the non-Yrast states and their decay properties to the corresponding states of 125Xe, which had been studied with similar methods in Cologne. The almost one-to-one correspondence between the states of these neighboring neutron-odd nuclei is a clear indication that their excitations at low spin remain collective well above the Yrast line. PACS 21.10. Re, 27.60+j It has been shown from extensive experimental studies, that the nuclei of the Xenon-Barium-region have triaxial deformation [1]. For the even-even nuclei some observables, such as the decay properties of the quasir indicate a 7-soft shape rather than a fixed value of 7 [2]. The available data on the odd-even nuclei, with observables such as the Yrast staggering, can also be explained with the Rigid Triaxial Rotor Particle Model (RTRP) assuming a smoothly varying triaxial deformation in the whole region [4]. These model calculations predict many negative parity states with low spin, which were found to match an experiment for 125Xe [3]. To establish the corresponding states in the neighboring odd-even nucleus 127Xe, will enable us to test not only the predictions of various collective models, such as the RTRP or the Interacting Boson Fermion Model (IBFM), but also to investigate systematically the properties of states, which go beyond the scope of the model calculations.The excited levels of l~Xe were populated with the 125Te(a, 2n) 127Xe reaction at beam energies of 23, 25 and 27 MeV at the Cologne FN TANDEM accelerator facility. The targot for the coincidence experiment consisted of enricheci 125Te (94%), which was rolled to a self supporting 5mg/cm 2 foil. The 77-coincidences were measured with the osiRis-cube-spectrometer, which was equipped with six high-purity-germanium detectors with asymmetrical anti-Compton-shields. In seven days of beam time, over 200 Mio. 77 coincidence events were registered and sorted into 4k x 4k matrices. In the analysis of the coincidence spectra, more than 300 transitions were placed into a level scheme, connecting 180 states, expanding the data of a previous experiment [5] by over 100 levels. The spin and parity of the excited states and the multipolarity of the 7-radiation was investigated with the angular correlation intensities of the coincidence measurement and with a separate angular distribution experiment. Furthermore, the sidefeedingerossection was analyzed from the 77 coincidence spectra at the three beam energies and used for assignment of spins as well.The resulting spectrum of negative parity levels of 127Xe and their branched 7-decay are compar...