How many decay events will be produced? Please explain to me what a "decay event" is... (more details below)

Question

Radioactive copper-64 decays with a half-life of 12.8 days.
(a) What is the value of k in s-1?
(b)A sample contains 28.0 mg Cu-64. How many decay events will be produced in the first second? Assume the atomic mass of Cu-64 is 64.0.

For part (a) I calculated K as .000000627 1/sec
I don't know what a decay event is and I can't figure it out in my textbook or online. If someone could please explain to me what a decay event is (is it the amount of times the balaned reaction goes to completion? is it the number of Cu atoms that decay?)

Also if you could show me how to solve part (b) or at least give me the equation you used and answer. It must be in units of decays/s. I'm assuming you use the equation ln(N/No)=-kt

Any information at all that you can give me will be extremely helpful! Thank you so much!

Answer 1

A decay event is simply an atom that decides to break down. K is the fraction of your material which decomposes per second. Work out how many atoms of Cu there are - 0.028/64 - and multiply by Avogadro's number and by k. This is how many atoms decay per second.
Multiply this by 1 sec to get the total number of decay events during the first second.