The use of radioisotopes in research on snow and runoff

Three radioactive snow gages were installed in the experimental area at the Central Sierra Snow Laboratory, during December 1949. A geiger tube was held by a 20-ft. Truss arm attached to a 50-ft. Pole. A lead shielded collimator imbedded in concrete beneath the truss arm held 2 units of radioactive Cobalt 60. Impulses of the geiger tube were amplified and transmitted over a 150-foot Cable to the recorder in the main laboratory. Largest sources of error were in variation of background impulses caused by cosmic rays. Four of 7 -- 5 minute counting periods each day gave accuracy within 2 to 5%. Water films of less than 0.01 inch to 55 inches can be measured by means of beta emissions from Strontium 90, and gamma rays from Cobalt 60.