1. The problem statement, all variables and given/known data A radioactive source emits electrons. The number of electrons emitted per second N(t) decreases with time according to the equation: dN/dt = −1.8 × 10−5N(t) , where t is expressed in seconds. If N = 12 electrons/sec at t = 0, after what time t has N fallen to the value 4.0 electrons/sec?  What is the half-life of the radioactive source in seconds?  2. Relevant equations 3. The attempt at a solution I have the first part done, but am confused about the second part. How can you tell the half life of the material from the information given? N is just the amount of electrons given off per second, and the half life is the amount of time taken for the amount of substance to halve right? I don't see how they can be directly related. Any ideas?