1. A method of wellbore operations comprising: providing a downhole tool having a pulsed neutron source and detectors; disposing the downhole tool in production tubing that is inserted in the wellbore; causing gamma rays to scatter into the wellbore by emitting neutrons from the tool into an annulus that circumscribes the tubular; detecting the gamma rays in the wellbore with the detectors to obtain a count rate of gamma rays detected by each of the detectors; obtaining a ratio of each of the count rates; comparing each of the ratios of count rates with a reference count rate ratio, the count rate ratios comprising ratios of count rates selected from the group consisting of inelastic gamma rays, capture gamma rays, and a combination of inelastic and capture gamma rays detected by detectors; and identifying the presence of weighting material in the annulus based on the step of comparing the ratios of the count rates.