1. A

    Find time required for remaining amount of radioactive substance

    I have a question in my online math course asking, A radioactive substance has a half-life of 20 days. i) How much time is required so that only 1/32 of the original amount remains? ii) Find the rate of decay at this time. So you have to love when there are questions after a lesson that ask...
  2. S

    The half life of a radioactive substance.

    I understand part a) as the equation is worked so that it is in terms of k. The solution for part b) is losing me at: \lambda=-\frac{ln(2)}{k}*y_0e^k^(^t^1^+ ^\lambda) I see that where t was before there is now the symbol lambda but the part after the * symbol is lost on me right now. Why is...
  3. S

    Logarithmic Functions, Radioactive Decay.

    The half-life of radium is 1,690 years. how long will it take for a 50-gram sample of radium to be reduced to 5 grams? The answer should be 5,614 years. The formula I'm using is Q(t)=Q0e-kt and I believe I am to use h= ln2/k. Here's what I've done: 5=50e(-k)(1,690) .1=e(-k)(1,690) ln...
  4. K

    Radioactive decay problem. Please help me !

    I've just been really thrown off by what this problem is asking me. Given: The decay of a radioactive material may be modeled by assuming that the amount A(t) of material present (in grams) at time t (minutes) decays at a rate proportional to the amount present, that is dA/dt= -kA for some...
  5. F

    Radioactive Logarithim

    Hey guys, just found this forum after searching for days about this problem I've got. No where seems to have any relevant answers so I thought I might ask a forum for some help. Basically I've got a Methods Assignment and I can't seem to work out if what I am doing is correct, any help would be...
  6. T

    A synthetic radioactive element decays at a rate proportional to its mass ....

    A synthetic radioactive element decays at a rate proportional to its mass. (a) write down a differential equation to represent this situation. (b) If 30% of the element has decayed after 24 hours, what percentage is left after 48 hours? c) How long does it take for 90% of the element to decay...
  7. F

    Radioactive Decay Problem

    An unknown radioactive element decays into non-radioactive substances. In days the radioactivity of a sample decreases by percent. What is the half life of the element in days? AND How long will it take for a sample of 100 mg to decay down to 60 mg? How many days?
  8. N

    finding the half life of a radioactive element

    Hi, Find the half-life of a radioactive element that decays according to the rule: dA dt = −0.012 A where A is the amount in kg present after t years. I know the equation is A=A0e^(-0.012t), but how do you find the half life? please help, thanks.
  9. D

    Radioactive decay

    Radium-226 has a half life of 1620 years. Find the time period during which a given mass of this material is reduced by one-quarter. Q= Ce^-rt should be the right equation? Stumped on how to set this up.
  10. A

    Radioactive decay

    Quantity of radioactive material after 20 years decayed to 50 grams, after 40 years it decayed to 20 grams.What was the amount of radioactive material to start with. In problems like this usually we were finding half life or time but never initial amount. Radioactive decay is given by...
  11. euclid2

    radioactive substance problem

    a radioactive substance has a half life of 20 days. i) how much time is required so that only 1/32 of the original amount remains? i can figure out it would take 5 half lives but i don't know how to show it mathematically ii) find the rate of decay at this time.
  12. B

    Radioactive Decay Problem?

    The problem I am having with this is that I learned how to solve this type of problem a long time ago and when I was taught it they used another type of formula with different letters so I am kind of lost: (Can you tell me what I got write and what I did wrong if the answer is incorrect-Thanks)...
  13. A


    Carbon-14 is a radioactive substance produced in the Earth's atmosphere and then absorbed by plants and animals on the surface of the earth. It has a half-life (the time it takes for half the amount of a sample to decay) of approximately 5730 years. Using this known piece of information...
  14. P

    Radioactive Decay

    A radioactive material is known to decay at a yearly rate proportional to the amount at each moment. There were 2000 grams of the material 10 years ago. There are 1990 grams right now. What is the half-life of the material? The equation to solve is P = P0e^kt. Where P = population, P0...
  15. Y

    radioactive decay word problem

    After t years, 50e^{-0.015t} pounds of a deposit of a radioactive substance remain. The average amount per year not lost by radioactive decay during the second hundred years is (A) 2.9 lb (B) 5.8 lb (C) 7.4 lb (D) 11.1 lb (E) none of these if it helps the answer is B but i need help how to get...
  16. B

    Radioactive Decay Problem

    I've been working with this problem for almost two weeks trying to find a good equation for the decay of Bismuth to no avail. Can someone give me insightful comments: Here's the problem: 1. The problem statement, all variables and given/known data In the radioactive decay series of Uranium...
  17. T

    Radio-active decay problem.

    I have the following equation. N/6= N*exp(-.0001216t) Then I want to solve to t, and the solution is ln(6)/.00001216 I must be missing something....why is ln(6) and not ln(1/6)?
  18. R

    Radioactive Decay

    If Forty percent of a radioactive substance decays in five years. By what percent does the substance decay each year?
  19. L

    Radioactive Decay

    The strength of a radioactive substance decreases 50% in a 30-day period. How long will it take for the radioactivity to decrease to 1% of its initial value?
  20. C

    Explanation for a series of numbers (radioactive Decay)

    Hello Again! Thank you to all who helped with my last problem! i sincerely appreciate it! I have done all the maths to calculate the radioactive decay of the three substances (a,b & c), but i have been asked by my tutor to describe the results over time (paying particular attention to limits)...