17 The circled points in Figure 18 represent the activity in d/m/l of the surface water (Table 1). The levels of radioac- tivity in the surface water samples in most instances exhibit approximately the same pattern as do the corrected values from l= the probe record, although in some cases differences do occur. The greatest variation between the two sets of data is found in the latter part of the trip after high levels of radioactiv- tty had been encountered in the area of stations 9B, © and D, oF The scintillation monitoring unit exhibited good stability of the electronic components. There were, however, three prob- lems encountered in the operation of the instrument: tention of contamination in the sea water system, (1) re- (2) failure of the photomultiplier tube as a result of vibration, and (3) build-up of static charges in the sea water from pumping through plastic pipe. This was partially corrected by scraping away a small portion of the rubber lining of the tank. Before the unit is used in subsequent operations it is suggested that the following changes be made: 1. Install a self-priming heavy duty pump with a capacity of 30-40 gallons per minute immediately ahead of the tank. 2. Use only metal pipe, not lined with-plastic or rubber. 3. Install grounding bars inside the tank for discharge of static charges in the water. 4, Direct the incoming stream of water downward inside the tank from a pipe parallel to and within three inches of the bottom of the tank. 5. | Install a three-inch valve on the bottom of the tank aN