The development of a particulate radioactive soil for detergency studies

A sample of kaolinite clay has been tagged by neutron irradiation. After an extended cooling period (18 months) to allow the short lived nuclides to decay, the clay is still sufficiently radioactive to use it in detergency studies. Extraction tests show that about 25% of the radioactivity is labile, i.e., removed by sodium tripolyphosphate but that the remainder is strongly fixed in the clay matrix, resisting extraction by built detergents. The clay has a number of nuclides emitting both beta and gamma radiation. Analytical methods for both types of radiation have been developed for use with fabrics and wash waters. The clay has been combined with the doubly labeled fatty soil ( 3 H and 14 C) to make a triply labeled particulate soil. Tergotometer runs with three test fabrics show good precision for all three labeled components of the soil. Redeposition measurements were also made and showed that a considerable fraction of the residual clay on a washed swatch may in fact be due to redeposition rather than retention. Some problems remain in the application of this synthetic soil: the padding step must be modified so that the clay is more tenaciously bound to the fabric; a more automatic method of padding is required to handle large numbers of samples; the specific activity of the clay should be increased so that liquid scintillation analysis for all three tagged components can be made on a single sample of wash water.