Find the half life of a radioactive substance that decays by 10% in 10 years.?

Question

I need some help with starting off this question. Please help me figure out this problem! :]

10 points

Answer 1

well u need to calculate in how many years the half of radioactive substance decays....

0.9^x = 0.5

x = log 0.5 / log 0.9

x = 6.58

6.58 * 10y = 65.8y

Answer 2

cessium??

Answer 3

I like to make up a number for the amount of atoms we start with say 1000 atoms.

y = 1000 atoms [e^(t)(k)]   k is just a constant that determines how fast it will decay

we also know

900 = 1000 [e^ 10(k)]   because it loses 100 atoms when t = 10

to solve for k apply a rule of natural log aka (ln).  Just bring down the exponents.

0.9 = e^ (10k)

ln(0.9) = 10k

k = -.010536

now that you have k, find the time that we have 500 atoms left