(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A piece of Am-241 has a radioactivity of 10kBq. Determine how much Am-241 it contains.

2. Relevant equations

[tex]N(t)=N_0(\frac{1}{2})^{t/T_{1/2}} [/tex]

3. The attempt at a solution

Let A be the activity

Let N be the number of atoms

We know that [tex]A(t)=A_0(\frac{1}{2})^{t/T_{1/2}}[/tex] We can set our initial time to zero, which gives us [tex]A(t)=10kBq=A_0[/tex].

Furthermore, we know that A(t)=-N(t). We also know that [tex]N(t)=N_0(\frac{1}{2})^{t/T_{1/2}} => N'(t)=-\frac{N_0ln2}{T_{1/2}}(\frac{1}{2})^{t/T_{1/2}}[/tex][tex]=>N'(0)=-\frac{N_0ln2}{T_{1/2}}=10kBq => N_0=\frac{10kBqT_{1/2}}{ln2}[/tex]. Now we use that one atom weights 241,0568229u and that the half-life is 432,2 y (I converted it to seconds). Then we get that the mass of our "piece" is approximately 78,7 micrograms. However, in the key it says 1,83 ng.

What am I doing wrong here?

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Am-241 radioactivity problem

**Physics Forums | Science Articles, Homework Help, Discussion**