If a human is exposed to radioactive materials but later they are removed from their body, does the human remain capable of contaminating others? Is there a decay curve for the risk of contagion, possibly correlated with the half life of the radioactive substances?
This is an excellent question.
Let us give an example of a procedure that some humans really need to be exposed to - and that is Radiation Therapy.
Radiation therapy is usually given to cancer patients to destroy a tumor. Technically, there are two methods of giving radiation to a patient for therapeutic purposes - External and Internal radiation therapy.
When we talk about External Radiation therapy, we are talking about radiation administered through a beam to a specific region of the body. Basically, it is non-invasive because it uses only a machine with a beam that directs radiation to the specific body part containing the tumor.
Since the radiation is given in relatively small doses, patients who receive external radiation therapy are not considered radioactive and do not need to take any special precautions during the time they are being treated. It is safe for friends, family, and children to be around them - OncoLink.
On the other hand, patients undergoing internal radiation therapy (brachytherapy) get radioactive implants to destroy the tumor. This procedure is considered invasive because doctors need to put the radioactive implants inside the body where the tumor is located. Commonly used radioactive substance in implants are cesium, gold, iodine, iridium, and palladium.
Different radioactive materials have different half-lives. This information helps the radiation therapy team to choose the type of material to use and plan the treatment regimen. It also determines how long radiation safety precautions must be taken following treatment - Canadian Cancer Society.
Furthermore, if high dosage is being used in the therapy, expect that a small amount of radiation will be left in the patient's body after the implants removal. As the American Cancer Society states that,
With internal radiation therapy, your body may give off a small amount of radiation for a short time.
If the radiation is contained in a temporary implant, you will be asked to stay in the hospital and may have to limit visitors during treatment. You also may be asked to stay a certain distance away from them. Pregnant women and children may not be allowed to visit you. Your body fluids are not radioactive. Once the implant is removed, your body will no longer give off radiation.
Permanent implants give off small doses of radiation over a few weeks to months as they slowly stop giving off radiation. The radiation usually doesn’t travel much farther than the area being treated, so the chances that others could be exposed to radiation is very small. Still, your health care team may ask you to take certain precautions such as staying away from small children and pregnant women, especially right after you get the implants. Again, body fluids and the things you use will not be radioactive.