LIGHT-SCATTERING AND ABSORPTION CAUSED BY BACTERIAL-ACTIVITY IN WATER

There is a growing class of elementary particle detectors, large-water Cerenkov detectors, that have a body of water (thousands of tons) as a sensitive medium. Particles are detected when they interact with the water and produce Cerenkov light, so detection efficiency relies on t he transparency of the water. These detectors are active typically for many years, so biological activity (primarily bacterial growth) is on e of the means by which the transparency of the water may be reduced. We present the results of a measurement of light scattering and absorp tion from a population of Escherichia coli in water, which is used as a model for bacteria in general. One can separate the scattering and a bsorption by varying the refractive index of the medium by using a sol ute of high molecular weight. We show that the results can be understo od simply in terms of light scattering from small spheres (radius appr oximate to wavelength) with an effective refractive index, n(b), plus a small amount of absorption in the ultraviolet. We compare this scatt ering with Rayleigh scattering in pure water.