Question

Part A You are using a Geiger counter to measure the activity of a radioactive substance over the course of several minutes. If the reading of 400. counts has diminished to 100. counts after 89.3 minutes , what is the half-life of this substance? Express your answer with the appropriate units. View Available Hint(s) t1/2 = Value Units Submit

Answer 1

Simple here initial amount of radiation has been decreased by a factor of 4 ( i.e 400/100 ) over this time period.

Since 4 = 2*2 by this what it means for initial one already 2 half lives have already passed.

Now these 89.3 minutes accounts for 2 half lives

So that half life of this substance is 89.3/2. = 44.65 minutes.

And for these 44.65 minutes the counter would register 200 counts.