# B Nuclear Decay with time (half-life,initial activity/ nuclei)

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1. Oct 30, 2016

### Treeps

Hi! I just keep having a hard time looking for the formula stating the relationship between half life, the initial number of unstable nuclei and the initial activity, can someone help me on that ?

To be more specific, here is a problem which can be solved using that formula:
"A substance has a half life of 100s, and starts with 1020 unstable nuclei.Calculate the initial activity, and from this work out the time taken for all of the nuclei to decay if the activity did not decrease with time"

The only formulas I could find were:
A (final activity)= A0*e-decay constant*time
N (final number of nuclei)= N0*e-decay constant*time
But nothing clearing expressing the relationship between A0 and N0

2. Oct 30, 2016

### Staff: Mentor

Activity is the process of nuclei "going away" (decaying) - a derivative should help.

3. Oct 31, 2016

### Treeps

Euh is it A0=N0*decay constant ?

4. Oct 31, 2016

### Staff: Mentor

Right.

5. Oct 31, 2016

### Treeps

Ok, thanks for your help !