Spontaneous fission of neutron-deficient fermium isotopes and the new nucleus 241Fm

Spontaneous fission of neutron-deficient fermium isotopes (N <= 144) was investigated. The nuclei were produced in fusion-evaporation reactions of Ar-40 beams with Pb-204,Pb-206-208 targets. Excitation functions of the two-and three-neutron evaporation channels were measured. The new isotope Fm-241 was identified, and its decay properties were determined. A previously made assignment of a 0.8 ms spontaneous-fission activity to the isotope Fm-242 could not be confirmed. Isomeric states were not observed in any of the investigated isotopes. The experiments were performed at the velocity filter SHIP of GSI in Darmstadt.