If Zera finds a rock in the forbidden zane that is tainted with pluton...
Answer:Given:
- Activity (A) of plutonium-239 in the rock = 100 Bq
- Half-life (t1/2) of plutonium-239 = 24,900 years
- Time elapsed (t) between explosion and discovery = 500 years
To Find:
- Number of plutonium-239 atoms in the rock when discovered
- Number of plutonium-239 atoms in the rock originally
Solution:
Number of Plutonium-239 Atoms in the Rock When Discovered:
The activity of a radioactive sample is defined as the number of decays per second. It is related to the number of radioactive atoms in the sample by the following equation:
A = λN
where A is the activity, λ is the decay constant, and N is the number of radioactive atoms.
We can rearrange this equation to solve for the number of radioactive atoms:
N = A/λ
The decay constant is related to the half-life by the following equation:
λ = ln(2)/t
1/2Substituting the given values, we get:
λ = ln(2)/24,900 = 2.784 x 10
-5 yr
-1N = A/λ = 100 Bq / 2.784 x 10
-5 yr
-1 = 3.59 x 10
6 radioactive atoms
Therefore, the rock contains 3.59 x 10
6 plutonium-239 atoms when discovered.
Number of Plutonium-239 Atoms in the Rock Originally:
The number of radioactive atoms in a sample decreases exponentially with time according to the following equation:
N(t) = N
0 e
-λtwhere N(t) is the number of radioactive atoms at time t, N
0 is the initial number of radioactive atoms, and e is the base of the natural logarithm.
Substituting the given values, we get:
N(t) = N
0 e
-λt = 3.59 x 10
6 e
-2.784 x 10-5 x 500 = 3.63 x 10
6 radioactive atoms
Therefore, the rock originally contained 3.63 x 10
6 plutonium-239 atoms.
Conclusion:
- The rock contains 3.59 x 106 plutonium-239 atoms when discovered.
- The rock originally contained 3.63 x 106 plutonium-239 atoms.