Nuclear fission studies with the IGISOL method and JYFLTRAP

Abstract

there is no unique model or theory which describes all aspects of this phenomenon. Experimental measurements of nuclear fission product distributions still remains quite a challenging task for modern technologies. In the present work nuclear fission is studied from the radioactive ion beam production point of view. Some models suggest that the neutron-induced fission can be more favorable for production of neutron-rich nuclides than the proton-induced fission. The general idea of this thesis is to compare all aspects of both approaches in connection with the IGISOL method. A new technique to determine independent fission product yields was suggested for the comparison. This technique has been tested with the proton-induced fission of actinide targets at different energies. The independent yields of the fission of 232Th induced by 25 MeV protons have been measured in this work. Although only relative independent yields can be obtained by this technique. An extraction of absolute values requires additional information such as the mass distribution. Despite this fact the technique is suitable to compare independent fission product distributions for isotopes of a specific chemical element. To perform measurements with neutron-induced fission a neutron source and a gas cell have been made and experimentally tested. The neutron source has been designed for a proton beam with energy of 30 MeV and intensity of 100 μA. A thick Be target has been chosen to produce an intensive neutron beam. The neutron intensity has been measured by the activation method and at the 0 angle is equal to 3·1010 neutrons/(s·sr·μA), which coincides with the simulated value and is in good agreement with other similar measurements. The design of the gas cell has been chosen to be very similar to that for the proton-induced fission. It has quite a simple construction without any electric and radio-frequency electrodes. The gas volume of approximately 150 cm3 provides an evacuation time of about tens of milliseconds. Due to the low fission rate and high radiation background several collecting foils have been installed to estimate main parameters of the gas cell. Radioactive ions produced in the neutron-induced fission were implanted into these foils. Later foils have been placed at a low background station and -spectra have been measured by the HPGe detector. Finally the independent fission yields for the neutron-induced fission could not be measured due to the very low radioactivity extracted from the gas cell. Main results of the work and probable further developments are discussed in the Summary.