Štúdium oneskoreného štiepenia po $\beta$-rozpade v izotopoch $^{178-182}$Tl

Topic of the thesis is $\beta$-delayed fission. We describe nuclear fission, more specifically $\beta$-delayed fission and its importance in the theoretical part of the thesis. We look briefly to four models of fission barriers (FRLDM, Thomas-Fermi, LSD and ETFSI model) and to $\alpha$- and $\beta$-decay of the nucleus. In the beginning of the experimental part of the thesis we describe ISOLDE facility at CERN and the detection setup of our experiment. In result part of the thesis, we are comparing models of fission barriers and analyzing data from the experiment IS466 –(2), which was undertook at ISOLDE. Four separate measurements were performed with the direct production of isotopes $^{178}$Tl, $^{180}$Tl, $^{182}$Tl and $^{202}$Fr. We evaluated delayed fission probabilities of produced isotopes $P_{βDF}\,$($^{178}$Tl) = (2,8 ± 1,1)$\times$10$^{-3}$, $P_{βDF}\,$($^{180}$Tl) = (3,9 ± 1,1)$\times$10$^{-5}$, $P_{βDF}\,$($^{182}$Tl) < 1,4$\times$10$^{-8}$ and $P_{βDF}\,$($^{202}$Fr) = (2,1 ± 0,4)$\times$10$^{-4}$. The value for $^{180}$Tl is in agreement with previous measurement, remaining three values were determined for the first time. We identified several products of decays in $\alpha$-spectra and derived $\alpha$-branching ratios. $\alpha$-branching ratio of $^{178}$Tl, b$_α$($^{178}$Tl) = 53(4) % was obtained for the first time. We re-measured branching ratios of isotopes $^{202}$Fr, $^{202m}$Fr, $^{180}$Tl, $^{176}$Pt, $^{174}$Au, $^{170}$Os, $^{202}$Po, $^{198}$Po, $^{194}$Bi and we obtained limits of branching ratios for isotopes $^{170}$Ir, $^{172}$Ir, $^{174}$Pt, $^{178}$Au, $^{198}$At and $^{198m}$At. In case of $^{202}$Fr and $^{202m}$Fr we shown, that at least one of these states has significantly higher branching ratio for the $\beta$-decay, than was reported in previous works.