Short answers, pulled from the story.
Soviet authorities detonated the first Soviet nuclear weapon on the 29th of August 1949 at 7:00 a.m. Kazakhstan Time. The explosion occurred at the Semipalatinsk Test Site within the Kazakh Soviet Socialist Republic.
United States Air Force WB-29 weather reconnaissance aircraft carried special filters to collect radioactive debris from the atmosphere. On the 3rd of September 1949, one such plane flew from Misawa Air Base in Japan to Eielson Air Force Base in Alaska to collect samples containing fission products.
The Kurchatov Institute received extensive intelligence on the American design during World War II through espionage cases involving Julius and Ethel Rosenberg. Venona project intercepts also provided critical details about the plutonium core construction methods used by Soviet engineers.
President Harry S. Truman publicly announced evidence of an atomic explosion on the 23rd of September 1949 stating that an atomic explosion had occurred within the U.S.S.R. within recent weeks. This announcement marked a turning point in the early Cold War period and signaled the beginning of a sustained nuclear arms race between the two superpowers.
Serial production of the RDS-1 weapon began officially in December 1951 after five weapons were completed as a pilot series by March 1950. The RDS-1 device remained in production from 1949 until 1951 while the Soviet Union stockpiled 29 bombs of this model by 1951.