Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
Nuclear Physics. Help Me Solve This Question.?
Solution of (^131 I) is used for thyroid scanning. Only 0.5ml is needed to inject. The half-life of (^131 I) is 8 days.
a) If the solution has been stored for 11 days, how many ml will be used for the same scanning?
b) If the quantity of injection each time is not over 8ml. What is the effective life of solution?
2 Answers
- KarlLv 61 decade agoFavorite Answer
Radioactive decay follows the equation
A(t) / A(0) = 2^(-t / T)
where A(t) is the activity of the nuclide at time t, and T is the half-life.
The activity at time t divided by the initial activity is equal to two raised to the power of the number of half-lives elapsed, times negative one.
a) If the iodine-131 solution has been sitting around for 11 days, t = 11 and T = 8.
A(t) / A(0) = 2^(-11/8) = 2^(-1.375) = 0.386
After 11 days of decay, the amount of solution needed to give the same quantity of I-131 increases by 1 / 0.386 = 2.59. You need to inject 2.59 * 0.5 = 1.295 ml.
b) If the I-131 is allowed to decay down to the point where you need to inject 8 ml to give the same dose half a ml would give at time zero, you need to find the time it takes for I-131 to decay down by a factor of 8 / 0.5 = 16.
16 is a nice number. It is 2 * 2 * 2 * 2. Each factor of two represents one half-life, so after four half-lives, the amount of I-131 has decayed down to 1/16 of the original activity.
Each half-life is eight days, so four half-lives is 32 days.
The effective life of the solution is 32 days.
