Fission resonances observed in the $$^{237}$$Np(d,pf) reaction and the fission barrier topology of $$^{238}$$Np

Abstract

AbstractThe fission probability of $$^{238}$$ 238 Np was measured as a function of the excitation energy in the energy range of E$$^* = 5.4 - 6.2$$ ∗ = 5.4 - 6.2 MeV in order to search for transmission fission resonances. A radioactive $$^{237}$$ 237 Np target was bombarded with deuterons of E$$_d$$ d = 12 MeV, whereas the energy of the protons was analyzed with a superior resolution of $$\varDelta $$ Δ E = 8 keV. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory in Garching employing the $$^{237}$$ 237 Np(d,pf) reaction. A group of fission resonances has been observed at excitation energies between E$$^* = 5.5 - 5.8$$ ∗ = 5.5 - 5.8 MeV, which could be ordered into three (superdeformed) rotational bands with a rotational parameter of $$\hbar ^2/2\varTheta = 3.507$$ ħ 2 / 2 Θ = 3.507 keV, and identified as the first direct observation of transition states composing rotational bands in an odd-odd nucleus as they appear above the top of the outer fission barrier. Nuclear reaction code (talys1.95) calculations were also performed to extract the multi-humped fission barrier parameters of $$^{238}$$ 238 Np by fitting them to the experimental data of the present (d,pf) and previous (n,f) experiments. The extracted barrier parameters also support the above interpretation of the observed resonances.