Nuclear Structure Studies in the Ge-As Region

• Main Author: Dorottya, Sohler
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1997
• Subjects: Analytical chemistry; Atomic physics; Calibration; Charged particles; Crystals; Energy; Experiments; Magnetic tape; Neutrons; Nuclear physics; Nuclear research; Optics; Protons; Radiation; Silicon wafers; Spectrum analysis; X-rays
• ISBN: 9798346312338

In the present dissertation I have reported on the results of investigation of the structure of 65Ge and68;72;73As nuclei. The aim of my work was to study the competition between the collective and single-particle degrees of freedom in these nuclei. For this purpose I have studied the structure of Ge and As nuclei by means of in-beam and e spectroscopic methods. 7.1 Methods The states of 72;73As nuclei were excited via (p n) reaction. Single , coincidence and internal conversion electron spectra were measured. The energies and intensities of the lines were determined by analysing the single spectra. The level schemes were constructed on the basis of the -coincidence relations, as well as energy and intensity balances.The parities of the levels of these nuclei were determined by using the conversion coeficients deduced from the intensity ratios of the corresponding conversion electron and lines. The spin values were determined from comparison of the relative excitation cross sections of the levels measured at several bombarding energies with Hauser-Feshbach nuclear reaction cross section calculations. The multipolarities of the transitions and the reanalysed former angular distribution data provided further information to make the spin assignments unambiguous or more accurate.The 65Ge and 68As nuclei were studied via the 12C+58Ni heavy-ion induced reaction at the NORDBALL multi-detector array equipped with 15 BGO-shielded Ge(HP) detectors and a-ray calorimeter of BaF2 crystals. For reaction channel selection a Si ball consisting of 21E type Si detectors and a neutron wall of 11 liquid scintillators were used.For identification of the rays several particle-gated spectra and matrices were sorted, and than subtracted from each other to eliminate the contaminating lines. The level schemes of 65Ge and 68As were constructed on the basis of coincidence matrices. The spin values of the excited states were deduced using the results of the simplified correlation analysis, which is sensitive for the angular momentum transferred by the rays.7.2 Results1. I have measured the energies and intensities of 112 transitions assigned to 72As, of which 57 were new. I have also determined the internal conversion coefficients for more than 50 (among them 38 new) transitions, and deduced their multipolarities. I proposed a more complete level scheme for 72As up to 850 keV, which contains 6 new states and more accurate spin-parity assignments for more than 30 states.2. I have measured the energies and intensities of the rays assigned to 73As. I have also determined the multipolarities. For 20 transitions belonging to 73As they were unknown earlier. I have deduced more accurate or unambiguous spin and parity values for 22 states the first time.3. I have significantly extended the level scheme of 68As up to the excitation energy of 6 MeV and J=(15+), containing 33 new transitions and 18 new states. I have deduced the multipole character of more than 30 transitions from the angular distribution ratios. I have found a new isomeric state at 1571 keV with a half life of 19-3 ns.4. I have assigned 21 new transitions to the 65Ge and proposed a new, more complete level scheme up to excitation energy 9 MeV with 17 new states from the total 25 ones. I have determined the spin values of the excited states up to (33/2).As a part of the program interacting boson-fermion(-fermion) model (IBF(F)M) calculations were performed for more than twenty nuclei in the Zn-As region by S. Brant, Lj. Simicic and V. Paar (Unversity of Zagreb) and by T. Fenyes (ATOMKI, Debrecen). The results of the IBF(F)M nuclear structure calculations were in reasonable agreement with the experimental level schemes, as well as electromagnetic moments and reduced transition probabilities. The low-lying states of 68;72As have many components, but in several cases the one-quasiparticle component was dominating. Many quasiparticle-plus-phonon states were also identified, especially in 65Ge and 73As.