Question

A certain radioactive isotope placed near a Geiger counter registers 160 counts per second. 32 hours later, the counter registers 10 counts per second. What is the half-life of the isotope?

A. 8 hours

B. 16 hours

C. 24 hours

D. 32 hours

E. none of the above

I thought it was E but I am wrong.

Answer 1

@ybarrap

Answer 2

it is D. i am almost positive.

Answer 3

It's going to be 8 hours. You'll have to use the half life equation to solve for t1/2:
\[\Large N(t)=N_0(\frac{1}{2})^{\frac{t}{\frac{1}{2}}}\]N(t) = the quantity that still remains and has not yet decayed after a time t
N0 = the initial quantity of the substance that will decay
t1/2 = the half-life of the decaying quantity

Answer 4

C and D don't even make sense knowing that this is an exponential decay problem :)

Answer 5

oh okay, thank you so much. my mistake.

Answer 6

Here's what a typical exponential decay graph would look like.