1. The problem statement, all variables and given/known data A stationary nucleus undergoes radioactive decay. A beta particle and a neutrino are detected leaving the nucleus. What is the recoil velocity of the remaining nucleus? If the recoil velocity measured is significantly different from the calculated velocity, what conclusion might a nuclear physicist reach about the decay? I've solved the first part of the question. As for the second part, it's been a long time since I took chemistry and there are no relevant examples in my textbook. 2. Relevant equations N/A 3. The attempt at a solution My guess is that there was another particle involved in the decay that was not detected. I realize I'm expected to figure stuff out on my own so it'd be great if someone could at least suggest what I should research. My Google searches haven't been very helpful.