Is this equation
is the initial amount of uranium at
You are told that at then
So you have
at
Dividing from each side leaving
Can you now solve for ?
A sample of uranium-239 (U-239) decays into neptunium-239 (Np-239) according to the standard decay function:
After 10 minutes, the sample has decayed to 64% of its initial amount.
a) The value of the disintegration constant, pi, is approximately 0.045/min
b) The half-life of U-239 is 15.5 minutes approximately.
(working on this at the moment)
c) Write the equation that gives the amount of U-239 remaining as a function of time, in terms of its half-life.
d) Suppose the initial sample had a mass of 25mg. How fast is the sample decaying after 15 minutes?
Hmm, this is how I tried solving for t:
As you said: No/2 = Noe^-pi(t)
I rewrote it as (0.5)( No) = Noe^-pi(t)
Divided No out..
0.5 = e^-pi(t)
ln(0.5) = ln(e^-pi(t))
ln(0.5) = -pi(t)
ln(0.5)/-pi = t
t = approximately 0.22
Where did I go wrong? The answer is 15.5 minutes
Just subbed in 0.043 for pi and the answer I got was -7..
Ooooh, worked it out and got the right answer
The next part asks for an equation that gives the amount of U-239 remaining as a function of time, in terms of its half-life.
The answer is N( t) = N0(1/2)^(t/15.4)
What are the steps one must take to get to this answer? And i'm looking at the exponent part.. t/15.4, and i'm wondering why is it not 15.5? Or is it something completely different?