1. The problem statement, all variables and given/known data 1 Curie corresponds to the number of decay in 1 gram radium-226 in 1 second. How many Bequerel is 1 Curie? 2. Relevant equations 3. The attempt at a solution Half life: 1600 years 1 gram = 0,001 kg = (0,001/1,660539*10^-27) u one Radium atom = 226,0260974 u Number of decays: (0,001/1,660539*10^-27)/226,0260974 Then I thought that since the half-life is so high that the activity won't change much in only 1 second so I though I could pretend that the activity is constant. So I just divided the number of decays with one second but my answer is wrong. In the key that I got from my teacher I am supposed to use this formula: A = lambda * N. Is it wrong to assume that the activity doesn't change so much in 1 second?