# Pls help me with my nuclear physics homework

1. Jul 24, 2007

### dansics

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

2. Relevant equations

3. The attempt at a solution

hello..im new to nuclear physics and i have problems attempting helf life questions.. hope you can help me with this question..

The half-life of a given radioactive isotope is 10 years. What is the mass of this isotope remaining undecayed after 20 years if the original mass was 12g? thank you..

2. Jul 24, 2007

### cristo

Staff Emeritus
Welcome to PF, dansics. Please note that for homework questions, you need to show some work before we can help you, as per forum rules.

What is the definition of half life?

3. Jul 24, 2007

### dansics

the defination of half-life is the time-taken for half the original unstable radioactive nuclei to decay.

4. Jul 24, 2007

### cristo

Staff Emeritus
Ok, so the question asks what mass is remaining after 20 years. How many half lives is this? What mass of the original isotope remains after one half life? From this can you say what mass remains after the number of half lives equivalent to 20 years?

5. Jul 24, 2007

### dansics

emm..so in 10 years, the mass is reduced to 6 g and in 20 years the mass is then reduced to 3g?
Am i right?

6. Jul 24, 2007

### cristo

Staff Emeritus
Yup, you are correct.