and resized (Sato, 1962; Taney, 1963). Radioactive material has been 

 plated on the surface as in the ORNL-developed gold technique utilized 

 in the RIST program. Radioactive gas (Krypton 85 and Xenon 133) has 

 been absorbed into quartz sand (Chleck, et al., 1963; Acree, et al., 

 1969) . 



While particular experiments employ specific sampling methods and 

 operational characteristics, there are basic elements in all tracing 

 studies. These are: (1) selection of a suitable tracer, (2) tagging 

 the particle, (3) placing the particle in the environment, and (4) 

 detection of the particle, either in situ or in a laboratory after 

 removal from the field location. For stable tracers, except in clear 

 water or on a beach at low tide, samples of the sediment must be removed 

 from the environment before the particle can be accurately detected. 

 Collection of the data requires physically counting or weighing the 

 sediment grains. In either nuclide or nonnuclide tracing, the particular 

 particle must be detected. With fluorescent pigments, the detection 

 is normally accomplished by an ultraviolet lamp. Sensitivity of this 

 technique is usually reported to be about 1 part in 10 million of the 

 sample examined. However, results are very dependent on the extent to 

 which the field area being studied can be sampled. Since dilution of 

 the tracer with natural sediment occurs rapidly, sampling is difficult. 

 As a result, most studies using a fluorescent material are restricted to 

 short periods of several hours. Also the number of samples that can be 

 collected and processed is limited because manual sampling and laboratory 

 analysis are time consuming. An automated device for counting fluorescent 

 particles, described by Teleki (1967) apparently has not had widespread 



When a radionuclide is used as the tracer, it is possible to detect 

 it at the field site. The xenon- 133 isotope- tagging technique was de- 

 veloped specifically for the RIST program, and is totally new to the 

 field of sediment tracing. Gold- 198 has been used numerous times in the 

 past, especially in studies to determine the dispersal pattern of silts 

 and clays, however, the gold-tagging technique developed for RIST 

 (Stephens, et al., 1969) is greatly improved since the tag is firmly 

 fixed to the grain so that detection of the isotope definitely shows 

 that a tagged sediment particle has been detected. The same statement 

 cannot be made with assurance for the previous gold-tagging techniques. 

 In all studies reported, a sled device was used to carry the radiation 

 detector over the bottom of the water body. Detectors are Geiger-Miiller 

 tubes or scintillation crystals. The collected data are on a continuous 

 strip chart, although in some cases digital printout has been used 

 (Hart, 1969; Courtois and Monaco, 1969). The field technique for locat- 

 ing the position of the detector sled, or more specifically, the vessel 

 towing the sled, has been by the usual surveying technique, when on a 

 given signal, two men operating surveying instruments read an angle of 

 sight to the vessel. This information is recorded and later drafted 

 by hand. 



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