[xavier]

I have a problem I can't answer and I need help with it:

How much time is required before 10mCi of Technetium 99m and 25 mCi of Indium 113m decay, assuming equal activities?

I would appreciate anyone who can solve it and send me the answer.

thanks

[Mitch]

You do your HW not us. You can look up the half-lives here http://www.isotope-table.com/

[Grejak]

Like Mitch, I am opposed to doing someone else’s homework and then sending it off to them.  Especially because you chose to take that course, not me.  However, I am willing to give hints.

I have a problem I can't answer and I need help with it:

How much time is required before 10mCi of Technetium 99m and 25 mCi of Indium 113m decay, assuming equal activities?

I think that is because the problem is very poorly worded.  mCi is a unit of activity, 3.7 x 10¹⁰ decays per second, while the question implies that it is a mass or moles etc.  It also reads as though you can assume an arbitrary initial activity and then calculate different times for both ^99mTc and ^113mIn.  Tell your professor that I said it was not a valid question, I am sure that he/she/it will listen to me…

Just in case that does not work though, I suspect that the question is actually supposed to read something like:

Assuming that you begin with equal activities of ^99mTc and ^113mIn, how long would it take for the activity of ^99mTc to decrease by 10 mCi.  During this time, the activity of ^113mIn must also decrease by 25 mCi.

You can use the website provided by Mitch to look up the decay information for ^99mTc and ^113mIn.  Then you can use the formula A = A₀e^(-lambda*t) for each isotope.  Since you know the decrease in activity during the time interval, you should be able to give a value of A in terms of A₀.

Then you have two variables and two equations, so simple algebra will give you an answer.

I would appreciate anyone who can solve it and send me the answer.

Yeah, I dont quite define "help" as "do it for me".