Determination of arsenic and gallium in standard materials by instrumental epithermal neutron activation analysis

Epithennal neutron activation analysis has been applied to the determination of arsenic and gallium in standard materials at trace concentrations. The reduction of ²⁴Na activity compared to thermal neutron activation is advantageous. Arsenic detection limits (1σ) are 0.04 and 0.015 μg for inorganic and organic materials, respectively. The corresponding gallium detection limits, for the best cases, are 0.13 and 0.29 μg. Gallium determinations with the 834-keV photopeak of ⁷²Ga suffered interferences attributed to the threshold reaction ⁵⁴Fe(n,p) ⁵⁴Mn; the less intense ⁷²Ga peaks at 629 and 2200 keV provided quantitative results for all samples tested. Gallium detection limits with the less intense, but more reliable 629-keV peak were 0.9 and 0.1 μg for inorganic and organic materials, respectively. Arsenic determinations are best performed with the more intense ⁷⁶As 559-keV line, as the 657-keV line has an unknown interference.