Re: Calculation Radioactive Isotope decay rate Message #4 Posted by Osvaldo Rodriguez on 12 Aug 2007, 12:34 p.m., in response to message #1 by Vincze
Vincze
One of the beauties of RPN and keystroke programming is that you program just as you would work out the problem. For Radioactive Decay, I prefer to use the integral form of first order reactions. All radioactive decay follows first order kinetics, which means that the following equations apply...
rate = k*[A]
upon integration you obtain
[A]t = [A]o Exp(k*t)
where [A]o is the initial concentration
k is the rate constant which can be found by Ln (2)/half life
t is the time of reaction and
[A]t is the amount left after time t has passed by.
For the HP 28c and the 48gx the programming is the same. Using local variables "a" for [A]o, "b" for half life and "c" for time you can enter the program as follows.
<< > a b c << 'a * EXP (  ( LN(2) / b ) * c ) ' >> >>
save it as 'decay' then enter the values into the stack and press 'decay' from the user menu.
for this program the values have to be [A]o , half life and time in that order into the stack.
if you do not want to use local variables a shorter program would be
<< 2 LN SWAP / * NEG EXP * >>
save it as 'dacay' or any name you want to give it then enter [A]o, time and half life into the stack in that order. The program will return the amount left over. This last program should also work for the 35s, even though I do not have one, I believe you just need to change SWAP for x<>y and NEG for +/.
Good luck
Sorry I had to edit to fix the formatting
Edited: 12 Aug 2007, 9:37 p.m.
