Production of Carrier-free ⁵⁴Mn by the α-Particle Bombardment of Natural Chromium

Abstract

For the production of ⁵⁴Mn by the α- and ³He-particle reactions on natural chromium, their excitation curves and thick-target yields were measured. Also various conditions in the production procedure, especially the chemical separation of manganese in a hydrochloric acid solution of the bombarded target after the removal of ⁵²Fe were examined. A stack of thin chromium plates was bombarded by α- or ³He-particles beam of 44 MeV maximum energy, and the manganese activities were measured nondestructively or after the chemical separation. The excitation curve of the α-reaction shows a maximum of 490 mb near 30 MeV energy, and that of the ³He-reaction, a maximum of 80 mb near 18 MeV. The thick-target yields for 40 MeV incident energy are 6 μCi/μAhr and 1.1, μCi/μAhr for the α-reaction and the ³Hereaction, respectively. The α-reaction thus proved to give a higher yield of ⁵⁴Mn than the other possible reactions. The bombarded chromium target was dissolved in a hydrochloric acid solution (8 N) from which the ⁵⁴Fe was removed by an extraction method. The remaining solution was saturated with a pure HC1 gas in such a way to bubbling it through the solution, from which almost all the non-radioactive chromium and other byproduced active contaminants were removed by an anion exchange method. The manganese solution thus obtained was evaporated to dryness, and the Cl^--free residue was dissolved in 50 ml of 10 mol/l H₂SO₄ together with 2 g of KIO₃. And then from the resulting solution the Mn was distilled out as Mn₂O₇ into a trap containing a small amounts of dilute HCl solution plus H₂O₂. To maintain the solution at 10 mol/l of sulfuric acid concentration and 166°C which is the optimum conditions for distillation, azeotropic nitric acid vapour (120.5°C) was added gradually into the boilling solution. The ⁵⁴Mn was obtained in carrier-free state. The chemical yields over all the chemical procedure proved to be >90% with a sufficient radiochemical purity. The production method of ⁵⁴Mn via the α-reactions on natural chromium proved to be superior in higher yields and some other reasons to other possible reactions.