Neutron activation analysis of aluminum in Mg2SiO4

An investigation of the role of aluminum in the enhancement of the near infrared lasing properties of chromium doped forsterite (Cr:Mg2SiO4) has led to the development of a neutron activation analysis (NAA) procedure for the trace analysis of aluminum in a silicon-containing matrix. After the initial analysis of a set of standards, this method requires only one irradiation per sample and relies upon the inherent nuclear properties of the silicono isotopes 28Si and 29Si. The 28Al signal produced by the activation reaction 27Al(n, γ)28Al, is interfered by the competing fast neutron reaction 28Si(n, p)28Al. Activation of an aluminum-free silicate will produce a constant ratio of 28Al and 29Al signals due to the 28Si(n, p)28Al and 29Si(n, p)29Al fast neutron reactions. Activation of an aluminum-doped sasmple will result in an increase in the 28Al signal due to the 27Al(n, γ)28Al thermal neutron reaction but have no effect on the 29Al signal. Therefore, any increase of the 28Al/29Al ratio in the doped silicate is due to the presence of aluminum. The subtraction of the 28Al/29Al ratio of the undoped sample from the 28Al/29Al ratio of the doped sample gave the portion of the 28Al signal resulting from the 27Al(n, γ)28Al reaction. Three forsterite single crystals with varying ratios of chromium to aluminum were grown for this study by the floating zone method using sol-gel derived feedstocks. Their compositions were determined by NAA using the correction procedure described above.