The recent development of the sediment concentration gauge consisting of a

238

Pu low-energy X-ray source

a proportional counter and a microcomputer is reported. The measuring method and its software

as well as the error analyses

are given. The minimum measurable sediment concentration is as low as 0.072 kg/m

3

and the standard error is 0.024 kg/m

3

. The effective measuring range of the probe is less than 5 cm

so the gauge is suitable for measuring the concentration of the sediment near the bottom of a river.