Question Video: Definition of Radioactive Contamination Physics

Video Transcript

Which of the following is the correct definition of contamination? A) The exposure of an object or material to radiation. B) The exposure of water or food to radiation. C) The deposition of radioactive substances on the surface of or inside an object. D) The death of living cells from exposure to high levels of radiation. E) The chemical reaction of radioactive substances with other substances.

Okay, so in this question, we’re discussing contamination, otherwise known as radioactive contamination. So let’s start by imagining that we’ve got a radioactive source. Let’s say that we’ve got a block of radioactive substance. And this block emits ionizing radiation such as alpha particles or beta particles or gamma rays. Now, in certain circumstances, we want things such as food and water to be exposed to the radiation that this block is emitting.

For example, if we take these pieces of fruit and veg and expose them to the ionizing radiation. Then the radiation can be used to kill any harmful microorganisms that are living in the fruit and veg. And so, we’ve willingly exposed our fruit and veg, or other foods, to ionizing radiation. Because it yields a positive outcome for us. It means we can eat food that isn’t going to give us food poisoning or even potentially kill us.

Therefore, simply exposing foods to ionizing radiation is not the same thing as contamination. And hence, if we look at option B, which says that the exposure of water or food to radiation is the correct definition of contamination. We could say that that option is totally incorrect. And actually, this principle applies generally as well.

If we look at option A, this one says that the exposure of an object or material to radiation is the correct definition of contamination. But this is not true either. Any object simply exposed to radiation is not considered contaminated. And hence, option A is not the answer to our question. In order to understand what contamination actually is, let’s continue thinking about our fruits and veg and the process that we would actually go through in order to irradiate our fruits and veg. Which essentially consists of somebody taking the radioactive source and moving it closer to the fruits and veg or vice versa. Actually, bringing the fruits and veg close to the source of radiation.

Either way, in exposing our fruits and veg to ionizing radiation, the person handling this needs to be very, very careful to ensure that they don’t first touch the source and then the fruits and veg. The reason for this is that even if the person uses gloves when handling the radioactive substance, small bits of radioactive substance may come off on their gloves. And then, when they go to handle the fruits and veg with the same pair of gloves. They might end up transferring some of the radioactive substance onto the fruits and veg.

And this is not a good thing at all. Because if the person had done things correctly, the fruits and veg would only be exposed to the radiation coming from the source. Which is fine, because that radiation passes through the fruits and veg and kills any harmful microorganisms on the way. But if they accidentally transfer some small chunks of the source itself onto the fruits and veg. Then the fruits and veg is now said to be contaminated with the radioactive source. And this is a very bad thing. Because even once we complete the entire process and take the fruits and veg away to the supermarket, for example, ready to be eaten. There is still some radioactive substance left over on the fruits and veg, either on the surface or even inside.

And that small amount of radioactive substance will also emit ionizing radiation. Which means that if a person eats the fruits and veg, then they have now ingested a radioactive source. This is highly dangerous. Because once ionizing radiation gets inside the body, it can wreak havoc. But the point is that contamination occurs when a radioactive substance is unwillingly or accidently placed on the surface of or inside an object where we do not want it to be. In other words, simply exposing an object to radiation is not enough to say that it’s contaminated. Because this is not always a bad thing. But transferring radioactive substances onto or inside the object is contamination.

So looking at option C then, we see that this option says, the deposition of radioactive substances on the surface of or inside an object is the correct definition of contamination. And going by what we’ve discussed so far, that is the correct definition of contamination.

Very quickly looking at option D, this one says that the death of living cells from exposure to high levels of radiation is contamination. And this is not true. Remember, we said earlier that we expose fruits and veg to ionizing radiation to kill microorganisms. And microorganisms are living, and many of them are cellular organisms. So killing these microorganisms is the death of living cells. But that’s not the same thing as contamination. And hence, option D is not what we’re looking for.

And finally, option E says that the chemical reaction of radioactive substances with other substances is the correct definition of contamination. However, we don’t need the radioactive substances, in this case placed on our fruits and veg, to react chemically with the fruits and veg itself. All we need is for the radioactive substance to be placed on or inside the object. It doesn’t need to react. It just needs to be there. And hence, option E is not what we’re looking for. Therefore, our final answer is that the correct definition of contamination is the deposition of radioactive substances on the surface of or inside an object.