Question: Recently I've conducted an experiment measuring the dose rate (in μR/h) from various samples (Ba-133, Cs-137, Co-60), at varying distances. In determining the efficiency of paper as a shield, it is required to convert the activity of the source to units of dinsintegrations/second (dps). On each of the sources was a label that stated the half-life. Additionally, each source said "1 μCi". So therefore, since 1 μCi = 3.7 x 10^4 dps, that would be the activity in dps. Correct? However, I don't understand how all of the sources could have the same activity in dps, but have different half-lives. Note: the half-lives given on the sources for Ba-133, Cs-137, and Co-60 are 10.5, 30.2, and 5.27 years, respectively.