Extra：How much 14C is radiatively decaying in your room? You yourself are also radiatively decayed.

　By the way, in the previous example, we set the initial number of 14C atoms to 2.61 x 10¹¹. With this number, one 14C atom will β-decay in exactly one second. We know that only 1.2 x 10^-12 (about one trillionth) of the carbon in the atmosphere is 14C. This means that if there are 2.61 x 10¹¹/(1.2 x 10^-12) (= 2.175 x 10²³) carbon atoms in the atmosphere (total of 12C, 13C, and 14C), one 14C atom will β-decay in one second. This total number of carbon (2.175 x 10²³) is 0.36 moles of carbon atoms. This is equivalent to the amount of carbon dioxide (400 ppm) in 20 m³ of air. If the classroom is 10 m x 10 m x 3 m, then 15 β-decays are occurring per second in the air of that classroom. In the human body, which is a mass of carbon, each person (weighing about 75 kg) has approximately 4,000 β-decays per second. This is a surprisingly familiar phenomenon.