Production of neptunium and plutonium nuclides from uranium carbide using 1.4-GeV protons

Accelerator-based techniques are one of the leading ways to produce radioactive nuclei. In this work, the isotope separation on-line method was employed at the CERN-ISOLDE facility to produce neptunium and plutonium from a uranium carbide target material using 1.4-GeV protons. Neptunium and plutonium were laser-ionized and extracted as 30-keV ion beams. A multireflection time-of-flight mass spectrometer was used for ion identification by means of time-of-flight measurements as well as for isobaric separation. Isotope shifts were investigated for the 395.6-nm ground state transition in 236,237,239Np and the 413.4-nm ground state transition in 236,239,240Pu. Rates of 235-241Np and 234-241Pu ions were measured and compared with predictions of in-target production mechanisms simulated with geant4 and fluka to elucidate the processes by which these nuclei, which contain more protons than the target nucleus, are formed. 241Pu is the heaviest nuclide produced and identified at a proton-accelerator-driven facility to date. We report the availability of neptunium and plutonium as two additional elements at CERN-ISOLDE and discuss the limit of accelerator-based isotope production at high-energy proton accelerator facilities for nuclides in the actinide region.