Help,emergency!!! With Nln Review Question 3 Days To Exam/half Life Decay

[MUCHO MACHO MURSE]

:lol2:help!!! i have the nln in three days and am having problems trying to figure out how to solve a problem such as this:

the half life of (131) i is 8.1 days. what fraction of a sample of (131) i will remain unchanged after 32.4 days of decay

a.) 1/2

b.) 1/4

c.) 1/8

d.) 1/16

i know the correct answer is d.) 1/16 but i do not know how to arrive at this answer.

any help would be greatly appreciated. also, if anyone can give any advice on how to handle half life problems in any other forms would also be greatly appreciated, hope to hear from you.

[fizz2Nurse]

I don't know the math equations but I think it's pretty straightforward.

32.4 days divided by half lives = 4

say your sample = 1

take 1 divided by your number of half lifes squared

eg: 1 divided by 4 squared = 1/16th

I could be wrong too! but I think thats the way to figure it.

[Daytonite, BSN, RN]

If you take the number 1 on your calculator and divide it in half (divide it by 2) four times, that would represent 4 half-life periods of 8.1 days or 32.4 days. The resulting figure on your calculator is 0.0625. The decimal equivalent of 1/16 is 0.0625.

[MUCHO MACHO MURSE]

If you take the number 1 on your calculator and divide it in half (divide it by 2) four times, that would represent 4 half-life periods of 8.1 days or 32.4 days. The resulting figure on your calculator is 0.0625. The decimal equivalent of 1/16 is 0.0625.

hi and thanks for your response, this sounds correct but how do I do this without a calculator. The NLN does not permit calculators. how do you divide 1 by 4 4 times, if I am understanding correctly? thanks again.

[MUCHO MACHO MURSE]

I don't know the math equations but I think it's pretty straightforward.

32.4 days divided by half lives = 4

say your sample = 1

take 1 divided by your number of half lifes squared

eg: 1 divided by 4 squared = 1/16th

I could be wrong too! but I think thats the way to figure it.

thank you for your response, I am not sure if I understand correctly. Does this sound correct:

1 divided by 4 squared =16 or 1/16. Why is it squared? Just trying to understand the logic.

[Daytonite, BSN, RN]

The logic of it is that whatever quantity you are given is divided in half (half life) so that only half of it is radioactive after 8.1 days. By using 1. . .the amount of radioactive I-131 after 8.1 days will be 0.5. That is 1 divided by 2, or simply 1/2 in it's decimal form. If you want to know how much I-131 will be left after 16.2 days you simply take the 0.5 and divide it by 2 again to obtain 0.25. After 24.3 days you divide the 0.25 by 2 to get 0.125. And finally, after 32.4 days you divide the 0.125 by 2 to get 0.0625.

If you are told the patient is given 150 millicuries of I-131 and asked how much will be radioactive after 16.2 days if the half life of the I-131 is 8.1 days you would merely divide the 150 by 2 to get 75 and then divide the result, 75, by 2 again to get 37.5 millicuries.

I think this is much easier to do than to put everything in terms of exponents.

[MUCHO MACHO MURSE]

The logic of it is that whatever quantity you are given is divided in half (half life) so that only half of it is radioactive after 8.1 days. By using 1. . .the amount of radioactive I-131 after 8.1 days will be 0.5. That is 1 divided by 2, or simply 1/2 in it's decimal form. If you want to know how much I-131 will be left after 16.2 days you simply take the 0.5 and divide it by 2 again to obtain 0.25. After 24.3 days you divide the 0.25 by 2 to get 0.125. And finally, after 32.4 days you divide the 0.125 by 2 to get 0.0625.

If you are told the patient is given 150 millicuries of I-131 and asked how much will be radioactive after 16.2 days if the half life of the I-131 is 8.1 days you would merely divide the 150 by 2 to get 75 and then divide the result, 75, by 2 again to get 37.5 millicuries.

I think this is much easier to do than to put everything in terms of exponents.

Wow!!!! It is crystal clean now. Thank you so much for explanation that actually got through my thick head. I won't be afraid of this question on the exam in two days. Thanks again. :thankya: