[maleamalik]

I have a few problems that I am stuck on:
1.gallium-68 has a half-life of 68.3 minutes. Are you likely to "run into" gallium-68 in nature? Explain.

2. uranium0238 has a half-life of 4,49 x 10 ^9^ years. Are you likely to "run into" uranium-238 in nature? Where would be the most likely place in the united states to find uranium-238? Explain.

3. a 40.5 g sample of throium-234 has a half-life of 25 days. How much will remain after 240 hours? What percentage of the original amount remains?

4. the half-life of polonium-218 is 3.0 minutes. If you start with 20.0 grams,how long will it take for only 1.0 grams to remain?

[Unknown008]

1. No, because in 68.3 min, approx one hour, half of it is 'gone'. And since nature was 'here' long ago, I don't think that the answer is yes.

2. Yes, contrary to gallium, uranium takes much more time to decompose to half its mass. For the location, I don't know since I'm not from the US, nor reside there.

For the others, I prefer not to reply for I would suggest you to do a graph. I don't really know the calculations for radioactivity. Perhapd others here will help you.

[ebaines]

The formula for doing the math is like this:



So for problem 3:



Note that the units of time must be consistent - here I converted 240 hours to 10 days. So you end up with 75.7% of what you started with.

For the last problem you need to solve for t:



It's easiest to do this using logarithms.