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 <math><msup><mrow/><mrow><mn>236</mn><mo>,</mo><mn>237</mn><mo>,</mo><mn>239</mn></mrow></msup><mi>Np</mi></math> and the 413.4-nm ground state transition in <math><msup><mrow/><mrow><mn>236</mn><mo>,</mo><mn>239</mn><mo>,</mo><mn>240</mn></mrow></msup><mi>Pu</mi></math>. Rates of <math><msup><mrow/><mrow><mn>235</mn><mo>–</mo><mn>241</mn></mrow></msup><mi>Np</mi></math> and <math><msup><mrow/><mrow><mn>234</mn><mo>–</mo><mn>241</mn></mrow></msup><mi>Pu</mi></math> 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. <math><msup><mrow/><mn>241</mn></msup><mi>Pu</mi></math> 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.