Number 126 (Story #2), April 28, 1993 by Phillip F. Schewe and Ben Stein THE RATE OF HELIUM BURNING IN MASSIVE STARS , particularly the ratio of two reactions---three helium nuclei fusing to form carbon-12 and helium and carbon fusing to form oxygen-16---determines the sequence by which heavy elements build up in stellar cores and the fateful chronology by which massive stars approach a supernova condition. The rate at which oxygen is produced, the so called S factor, has now been measured in two separate experiments. (The carbon production rate had been previously measured.) Speaking at the April APS meeting, Moshi Gai of Yale and Lothar Buchmann of TRIUMPH (British Columbia) described their respective studies of the decay of oxygen-16 into carbon and helium. It was necessary to measure this reverse reaction because the fusion rate for carbon and helium, at least under lab conditions on Earth, was prohibitively small. The two experimental results were rather similar and largely in agreement with theoretical calculations. (Science, 2 April; Science News, 24 April 1993.)