A community for students.

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing


  • 4 years ago

Strontium-90 has a half-life of 29 years. In how many years will a 1 kg sample of strontium-90 decay and reduce to 0.25 kg of strontium-90? Answer 58 years 116 years 87 years 29 years

  • This Question is Closed
  1. anonymous
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    58 years. Use this expression: \[\ aA=Ae^{-kt} \] Where: A - is the initial amount (1 kg) a - percentage of A left after time t ( 0<a<1 ) k - constant (that you can find from knowing the half-life) t - time passed So you know that after t=29 years there is 0.5A left. From that you can calculate k and use it to calculate how much time it takes to drop to 0.25 percent of initial amount. It is even easier to do this if you notice that 0.25 is half of half life. So it drops by a half in 29 years and by another half in another 29 years. In each 29 years the amount halves itself. so it goes: 0 years - 1kg 29 years- 1/2*1kg 2*29years - 1/2*1/2 *1kg (this is what you are asked for) 3*29years- 1/2*1/2*1/2*1kg 4*29years -1/2*1/2*1/2*1/2*1kg

  2. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...


  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.