• Support PF! Buy your school textbooks, materials and every day products Here!

Half life questions

  • Thread starter dev-hud
  • Start date
16
0
i am taking upgrading, and one of the main reasons i failed physics 30 to start with was due to half life. the book cant explain it good enough to me and either could my teacher. so i have a few questions that i would appreciate a starting point for.

How much time elapses before 90% of the radioactivity of a sample of 72/33As dissapears as measured by its activity? the half life is 26h.


A sample of radioactive material contains 10^15 atoms and has an activity of 6.00 x 10^11 Bq. What is the half life?

these are just a couple of the many questions i am struggling with.
 
671
2
[tex]N(t)=N_0 e^{-t/\tau}[/tex]

Is all you need to know, along with the definition that the half life is the time it takes for half a given sample to decay.

After a time [tex]t=t_{1/2}[/tex] it holds that: [tex]N(t)=\tfrac{1}{2}N_0[/tex]

Looking at the general form, we find that:
[tex]\tfrac{1}{2}=e^{-t_{1/2}/\tau}[/tex]

Some algebra provides: [tex]\tau = \frac{t_{1/2}}{\ln{2}}[/tex]

Now try and solve the problems and show us where you have difficulty.
 
156
0
[tex]N(t)=N_0 e^{-t/\tau}[/tex]

Is all you need to know, along with the definition that the half life is the time it takes for half a given sample to decay.

After a time [tex]t=t_{1/2}[/tex] it holds that: [tex]N(t)=\tfrac{1}{2}N_0[/tex]

Looking at the general form, we find that:
[tex]\tfrac{1}{2}=e^{-t_{1/2}/\tau}[/tex]

Some algebra provides: [tex]\tau = \frac{t_{1/2}}{\ln{2}}[/tex]

Now try and solve the problems and show us where you have difficulty.
Don't feel bad if you don't agree that logarithmic manipulations aren't algebraic, I don't either. Doesn't mean they don't work.
 

Related Threads for: Half life questions

  • Last Post
Replies
10
Views
1K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
4
Views
3K
Replies
0
Views
7K
  • Last Post
Replies
2
Views
2K
  • Last Post
2
Replies
30
Views
11K
Top