this is a half-life ?

Question

A patient receives iodine-131 as a medical treatment on Monday, Sept. 11 at 11:00 am. On what date will only 1/4 of the original sample still be radioactive?
and can someone explain too...thanx =D

oh and half-life of iodine 131 is 8.07 days

Answer 1

half life of iodine 131 is 8 days

to get 1/4 of original, you need 16 days

T1/2 = 8k Amount = 0.5 of original

T1/4 = 2*8 = 16
Amount = 0.5 * (amount 8 days ago)
AMount = 0.5 * 0.5 (original amount)
Amount = 0.25 of original amount

sept 11 + 16 = sept 27 at 11 am.

Answer 2

For some mass of a radioactive element, the half-life is the time it takes for its (gamma) radiation output rate (I think that's usually measured in Roentgens per hour) to diminish by half. The number of atoms decaying into a non-radioactive form with each half-life is an approximation and it is not strictly stepwise, but it is continuous. The number of atoms that become non-radioactive is not so significant as the fact that the entire sample is putting out radiation at half the rate with the passage of each half-life, and the reason is that half the atoms are radiating at that time as were at the beginning of the time-measurement.

You could say the total amount of radiation being emitted is half as much with each passage of a half-life, measured from any starting point. That radiation, of course, is coming from ONLY those atoms that are still radioactive.

Not being familiar with the source of radioactive iodine-131, I don't know what "fully radioactive" means, but I'll assume a radiologist needs to know when his supply becomes useless (too weak to use). My guess is that the radiologist merely needs to know the amount of radiation coming off his sample to know how much to put into the radiation-limiting machine.

From any starting point, the radiologist knows that the radiation output will be halved about 8 hours and 4 minutes after he measured out his element dose. So, for your example, the radiation output is about half the starting rate at 7:04 pm on Sept. 11, and 1/4 the starting rate at 3:08 am on Tuesday Sept. 12. There's no way that I know of, for the intensity (rate of radiation) to be altered, except by starting over with a different quantity of the element, to give a different initial radiation exposure rate. An alternative but easier method of controlling the dosage is to time the exposure instead of measuring the element quantity. For a given number of Roentgens, the time for exposure (whatever it should be), needs to be doubled after the Iodine-131 sample is another 8 hours and 4 minutes older. This way the element does not have to be handled. You can see that careful, accurate, record-keeping about the element is necessary to give the patient the proper (adequate and safe) treatment.

Answer 3

Without being given the starting activity I can't be as accurate, if I had the activity I could get down to the minute it was a quarter of the activity. But hypothetically, it would be a quarter of its physical activity on Sept. 28th. But also take in consideration that not all of that I131 you were administered just stays in your body once you've ingested it. There is also biological half-life to consider, which is the time it takes the body to excrete half of the radioactivity it has taken in. I don't have my books right in front of me so I don't know the exact biological half-life of I131 off the top of my head. But consider that your salivary glands excrete some of the I131 and some (small percentage) is excreted through the kidneys, thus the urine. So perhaps a quarter of the original activity administered to you on Sept. 11th would remain actually in you on late Sept. 25th or early Sept. 26th.

Answer 4

The half-life of I-131 is 8.06 days. In 8.06 days, the radioactivity will be 1/2. In 8.06 days more, the radioactivity will be 1/4. The total is 16.12 days. The date will be Sept. 27. 0.12 days will be 0.12day x 24hr/1day = 0.005hr. So the time will not be much after 11 a.m.

Answer 5

on the 27th.

the halflife of iodine 131 is about eight days. the number 1 has to be halved twice to get 1/4, so you multiply eight by 2, and that tells you how many days.