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DEC 2 1965, DEC 5 1965 Three scientists seat themselves in a chamber at the end of the Schwartzwalder Mine north of Golden to test the effect of radon gas. From front to rear are Al Hazle and Dr. John Emerson, radiological health specialists, and Bob Siek, senior industrial hygienist, all with the Colorado health Department. They take off the face masks after the chamber is cleared. At right are air sampling instruments to determine size of dust particles and concentration of radioactive materials. Credit: Denver Post (Denver Post via Getty Images)