A strip-chart recording of the normal background radiation count shows small 

 oscillations (0.01 mR/hr), and wave periods of about 2 minutes. Normal 

 background count fluctuates between 0.0007 and 0.017 mR/hr. No appreciable 

 diurnal nor tidal cycle variation in radioactivity has been detected. 





Gonyaulax polyedra 



1145 



As the patches of Gonyaulax polyedra pass the sensor unit during a "red 

 tide," readings of 2.0, 3.5, 5.0, and in some instances greater than 5.0 mR/hr 

 have been observed. They last from 1 to 10 minutes. The high count is 

 attributed to the apparent ability of certain phy toplankton to concentrate 

 radioactive phosphorus from sea water. The highest rises in radioactivity 

 occur in the summer. 



77 



