# Homework Help: Radioactivity problem - Interpretation

1. Sep 21, 2008

### bachmusico

Hi! I should solve this exercise (quite important for me, because related to an important test I should sit next week) but I'm having some trouble with the right interpretation of the problem statement.

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

In which one of the radioactive series do you think the presence of artificial radioisotopes is possible?

2. Relevant equations

Maybe radioactive elements decay law, activity equation.

3. The attempt at a solution

I haven't been studying physics for a long time, but I've formulated my hypothesis.

The question refers to the so-called neptunium series, which can be observed as a whole only if artificial radioisotopes are producted. In fact the members of the series are concentrated in a sample of the longest-lived member, from which they derive, in concentrations proportional to the activity of each member. So, if the longest-lived member (in this case 237NP) has an half-life considerably inferior to the age of the Earth, we can assume that its concentration on the Earth has become too low to be traceable (almost exhausted). The exhaustion of the longest-lived member leads necessarily to the exhaustion of the whole series, which quite soon becomes transformed in the last, stable, member of te series. So, if we want to observe the series again, we are obliged to obtain the longest-lived member, the "parent" of the other members, following an artificial process, i. e. performing a nuclear reaction.
So we can say: the presence of artificial radiosotopes is possible in the neptunium series.​

But, as you can see, the formulation of the problem statement is rather "strange" for my solution (but that could be quite normal for the teacher who gave me this assignment), although other ideas I've formulated sound even more absurd. Moreover, the book I'm using to study (which is by the same author of the problem we are dealing with) doesn't mention the neptunium series at all, pointing towards other possible solutions, but what?

Could you help me? Do you agree with my solution or have any other idea?

Thank you very much