Background: The D-T controllable neutron source is used to replace the chemical gamma source to measure the formation density in oil exploration. Purpose: The paper aims to study the effect of pair production on density measurement accuracy using the D-T neutron induced gamma ray. Methods: Firstly

the theory of traditional chemical source density logging method is analyzed

and the difference of the mass attenuation coefficient between Compton scattering and pair production is compared. In addition

the measurement accuracies of both traditional density log and neutron induced gamma density log are studied using Monte Carlo simulation method. And then the source of error and its correction are analyzed. Results & Conclusion: The measurement accuracy of neutron induced gamma density is worse than the traditional density log

the reason is that the contribution of gamma comes from not only the Campton scattering

which is employed in traditional density log

but also pair production. Moreover

the pair production of gamma ray is sensitive to the formation lithology

and the measurement accuracy could be increased if the lithology correction was added. Abstract