In an experiment with the radioactive isotope $^{220}_{86}Rn$ of radon gas, Rutherford made the following measurements of the quotient $\frac{y'(t)}{y(0)}$ of the decay rates for the specimen he was studying: in $t = 40s$, $\frac{y'(t)}{y(0)} = 0.60$; in $t = 80 s$, $\frac{y'(t)}{y(0)} = 0.36$; in $t = 120 s$, $\frac{y'(t)}{y(0)} = 0.22$.
a) Draw the graph of the points $(0, 0)$, $(40, ln(0.60))$, $(80, ln(0.36))$, $(120, ln(0.22))$ in $\mathbb{R}^2$. These four points can be approximated to a line $-λ$, what is the value of lambda $λ$? This $λ$ is called the decay or decay constant of the element.
b) Find the function $y(t)$, which is the number of atoms at a time $t$.
c) The half-life of a radioactive element is the time it takes for the specimen to decay to half its initial size. What is the half-life of $^{220}_{86}Rn$?
d) What fraction of the initial number of atoms $y_0$ that remained after 5 minutes?
e) Assuming that $y_0 = y(0) = 10^9$, How many atoms disintegrated in 2 seconds? What was the average rate of disintegration per second over these two seconds? What was the rate of decay per second at $t = 2 s$?