1. Oct 4, 2011

There are 2 radioactive balls, which have the same radius and the same weight. They are covered with absorbing layer. They are made of diffrent materials, with other half-life. What is the easiest way to recognise which is which?
I had searched for the answer for a longer time and could not find out. Please for help.

2. Oct 4, 2011

daveb

What do you mean by an absorbing layer? Do you mean the layer absorbs all of the radiated particles and energy from the radioactivity?

3. Oct 4, 2011

sophiecentaur

You could, in principle, measure a change in densities somehow? ( Hint.)

4. Oct 4, 2011

256bits

If you had the 2 balls with different levels of radiactivity immersed ( frak - I had to look up how to spell that word ) in seperate baths of water in inslolated containers each with thermal instrumentation, could you devise a way to tell them apart?

5. Oct 5, 2011

thank you very much. that's a great idea to measure their densities or temperatures. i think, that one with density is the easiest one. you put them in water and the ball which has longer half-life would move down faster.

Last edited: Oct 5, 2011
6. Oct 5, 2011

yes.

7. Oct 5, 2011

sophiecentaur

But remember, the problem, I think, demands that all products of the reaction stay within the ball. So how would you measures density change and 'which' densities would change?

8. Oct 5, 2011

Matterwave

I vote for spinning the ball. If there is a layer (like skin) absorbing the radiated particles, then the moment of inertia of the balls should change at different rates.

9. Oct 5, 2011

sophiecentaur

Go for it my son.

10. Oct 5, 2011

csmcmillion

My g/f says I have two radioactive balls. ;-)

Last edited: Oct 5, 2011
11. Oct 5, 2011

sophiecentaur

How fast are they decaying?

12. Oct 5, 2011

csmcmillion

> How fast are they decaying?

Pretty fast these days. The interesting thing is that the decay rate is highly non-linear lately. I observed no decay in the first 20 years, a linear decay in the next ten years, somewhat of a geometric rate in years 30- 40, but since year 40 the rate appears to be exponential.

I have no rational explanation for my observations.

13. Oct 5, 2011

sophiecentaur

Use it or lose it my friend. No reason for things to fizzle out before the age of ninety!