On spontaneous fission of neutron-deficient isotopes of elements 103, 105 and 107

Experiments are described on the determination of the spontaneous fission probability for the isotopes of elements 103, 105 and 107 produced by bombarding Tl, Pb and Bi targets with 50Ti, 51V, 54Cr, 55Mn and 58Fe ions. The upper limit of the spontaneous fission probability is established to be 2% for the isotopes 252253 103. A new isotope of element 105 with mass number 257(Tsub(1/2)=5s) has been produced. In bombardment of 209Bi with 54Cr ions a new spontaneous fission activity with Tsub(1/2) approximately 1-2 ms has been observed. The experimental data permit identification of this activity as the isotope of the new element 107 with mass number 261, which mainly undergoes α-decay (approximately 80%) resulting in the formation of the isotope 257105. The values of the partial α-decay and spontaneous fission half-lives of the isotopes 257105 and 261107 are compared with the systematics of the properties of transfermium nuclei. (Auth.)