Radioactivity 



Continuous monitoring of sea 

 water for gamma rays is carried out 

 with a scintillation meter system to 

 establish a background level and to relate 

 any changes to biological or other causes. 

 The background is normally very low, 

 running 0. 007 to 0. 017 mR/hr. This 

 level is maintained for long periods of 

 time. However, occasional increases 

 in radioactivity over normal background 

 have been observed, especially in sum- 

 mer. 



Further investigation correlated 

 this significant intensification in radiation 

 with occasional blooming of the phyto- 

 plankton Gonyaulax polyedra. Thus, 

 increased radioactivity can usually be 

 correlated with high water turbidity. 



76 



Heart of the radiation detection system is this gamma 

 ray sensor, mounted 10 feet below mean tide level. 

 Amplified signals of radiation intensity are trans- 

 mitted through electric cables to a recorder in the 

 instrument house. Instrumentation sensitivity ranges 

 are to 0.05, to 0.5, to 5.0, and to 500 mR/hr. 

 Because of the normally low background count, the 

 recorder is usually set on the 0- to 0.5- mR/hr scale. 



