Suppose, the daughter nucleus in a nuclear decay is itself radioactive. Let `lambda_p and lambda_d` be the decay constants of the parent and the daughter nuclei. Also, let `N_p and N_d` be the number of parent and daughter nuclei at time `t`. Find the condition for which the number of daughter nuclei becomes constant.

Explanation

To find the condition under which the number of daughter nuclei becomes constant in a radioactive decay process where the daughter nucleus is also radioactive, we can follow these steps:

### Step-by-Step Solution:

1. **Define the Variables**:
- Let \( N_p \) be the number of parent nuclei at time \( t \).
- Let \( N_d \) be the number of daughter nuclei at time \( t \).
- Let \( \lambda_p \) be the decay constant of the parent nuclei.
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