00:04
Gallium 67 has a half -life of 78 .25 hours.
00:10
If we start with an initial mass of 0 .015 micrograms of gallium 67, and we allow it to decay for 13 days, we can figure out the mass remaining at the end of that time.
00:26
The first thing that we have to do is we notice that the total time is in days and the half -time, half -life is in hours.
00:34
So we have to convert days to hours.
00:37
So we have 13 days times 24 hours per day.
00:49
It's going to give us 312 hours.
00:53
And the second thing that we have to do is figure out how many half -lives have passed in that 312 hours.
01:00
So we take our total time, our 312 hours.
01:06
And we divide it by our half -life, which is 78 .25 hours.
01:18
And we find that in 312 hours, four half -lives have passed by.
01:27
312 divided by 78 .25 gives us four half -lives.
01:32
So at the end of every half -life, half of the mass remains.
01:40
So starting at time zero, no half -lives have passed by...