In vivo neutron activation analysis measurements of calcium using the 40Ca(n, α)37Ar reaction

An in vivo neutron activation analysis (IVNAA) technique is used to measure calcium. When the subject is irradiated with fast neutrons one of the reactions induced is 40Ca(n, α)37Ar. The argon produced is eventually collected as part of the mixture of exhaled gases, which is processed to remove the unwanted O2, N2, CO2 and H2O. The activity of the 37Ar is monitored in a gas proportional counter. The system has a reproducibility of about 2% when applied to animal studies.