Join in on our 'Guess the Rep' Competition! >>

Physics radioactivity

Tritium has a half life of about 12 years. If you put 3.0μg of tritium into a luminous sign, how much will still be there 50 years later.

Anyone have idea in this question? I found lambda here but not sure what to do next.

Many Thanksss.

Reply 1

Joinedup

About 12 years is about 1/4 of 50 years.

So theres a sumple method that might be accurate enough for multi choice

Reply 2

nighting.gale21

Original post by Ka.L

Tritium has a half life of about 12 years. If you put 3.0μg of tritium into a luminous sign, how much will still be there 50 years later.
Anyone have idea in this question? I found lambda here but not sure what to do next.
Many Thanksss.

Hey, I think you can treat it just like an algebra question. I did:

12->24->36->48 so 3 half lives experienced, therefore 3x10^-9 kg / 2^3 = 3.75x10^10 kg

and then you have the last 2 years and if it decays by 1/2 in 12 years, a sixth of that would be how much it decays in 2 years so 1/12 so times the answers above by 11/12 as you would've lost 1/12.

so final answer is 11/12(3.75x10^10 kg) = 3.44x10^-10 kg ???

Hope that helps

Reply 3

Joinedup

Original post by nighting.gale21

Hey, I think you can treat it just like an algebra question. I did:
12->24->36->48 so 3 half lives experienced, therefore 3x10^-9 kg / 2^3 = 3.75x10^10 kg
and then you have the last 2 years and if it decays by 1/2 in 12 years, a sixth of that would be how much it decays in 2 years so 1/12 so times the answers above by 11/12 as you would've lost 1/12.
so final answer is 11/12(3.75x10^10 kg) = 3.44x10^-10 kg ???
Hope that helps

Should be 4 half lives.

Now to year 12... 1 x half life
Year 12 to year 24... 2 x half life
Year 24 to year 36... 3 x half life
Year 36 to year 48... 4 x half life

Id say that's enough as the question says the half life is about 12 years.... And 12.5 is about 12
And 12.5 is exactly 50/4