Backscatter silt density gauge [Paper No. NT-7]

This paper describes a development of a portable digital electronic instrument, based on the principle of gamma ray backscatter measurement, designed specifically for the insitu measurement of subsqueous silt density for use in hydrographic survey aimed at defining sea bed for navigation purposes. The system consists of a nuclear backscatter probe in which use of small source to detector distance of 30 mm and NaI(Tl) scintillator has enabled operation with low activity of 150 μCi of cobalt-60 radiation source. The digital display provides direct readout of silt density. The paper also describes initial trials carried out at Mangalore Port upto a depth of 20 meters. (author)