Detection of trace amounts of manganese isotopes by surface ionization method.

Mass spectrometric determinations for trace amounts of radioactive 54 Mn and 53Mn in the presence of 55Mn have been studied. Both 54Mn and 53Mn are readily produced by nuclear reactions. Absolute amounts of each isotope could be obtained from the disintegration rate of 54Mn and the isotope ratios of 54Mn to the others. In order to find suitable experimental conditions in the isotope ratio, measure ments, a commercially available“ carrier-free 54Mn” was used as the sample.The manganese fraction was extracted from the sample containing 107 dpm of 54Mn and was puri fied for our mass spectrometric measurements by a wet chemical method. A silica gel method was applied for the solid source surface ionization and a pulse-counting method was improved to measure the extremely weak ion beam current. In one run about 1011 atoms of 54Mn could be determined with a high reproducibility in the presence of about 1014 atoms of 55Mn. Furthermore, coexisting 53Mn at the level of 10 10 atoms could also be detected with about±10%error.This method has been applied to determine the production cross-sections of 54Mn and 53Mn induced in a cyclotron-irradiated iron target.