The Nucleus - Laws

Law of radioactive decay

N = N₀e^{- λ t}

where
N = number of active nuclei at time t

N₀ = number of active nuclei at t = 0.

λ = decay constant


-dN/dt = λN

-dN/dt give the number of decays per unit time and is called the activity (A) of the sample

A = λN

A = A₀e^{- λ t}

Lawson criterion for fusion reactor

In order to get an energy output greater than the energy input, a fusion reactor should achive

n τ >10^14 s/cm³

where
n = the density of the interacting particles

τ = confinement time

the quantity n τ in s/cm³ is called Lawson number