Video: Stating the Definition of Background Radiation

Which of the following statements is the correct definition of background radiation? [A] Background radiation is any electrically neutral radiation. [B] Background radiation is low-level radiation from the surrounding environment which is not due to the deliberate introduction of radiation sources. [C] Background radiation is any low-energy electromagnetic radiation. [D] Background radiation is any radiation from sources that have a half-life of less than 1 minute.

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Video Transcript

Which of the following statements is the correct definition of background radiation? A) Background radiation is any electrically neutral radiation. B) Background radiation is low-level radiation from the surrounding environment, which is not due to the deliberate introduction of radiation sources. C) Background radiation is any low-energy electromagnetic radiation. D) Background radiation is any radiation from sources that have a half-life of less than one minute.

Okay, so to answer this question, let’s start by recalling that background radiation is low-level radiation that’s present everywhere on Earth. The amount of background radiation does vary from place to place. But in general, it’s very low level, and for that reason it’s not really harmful to humans. It occurs mainly due to naturally occurring radioactive substances found in the rocks beneath the earth and in the air around us. But there are some man-made causes to it as well.

For example, if we look at this pie chart, which shows us the percentages of background radiation produced by different sources, then we can see that the majority of it, 41.6% of all background radiation, is due to radon gas found in the air. And this radon gas is naturally occurring, but the next largest source is medical sources at 19.8%, for example, when radioactive isotopes are used to treat cancer. But the point is that all of these sources are not deliberate introductions of radioactive substances to the local environment. They’re either naturally occurring or a by-product of something man-made. And as well as this, as we mentioned earlier, background radiation is very low-level. And that there isn’t a lot of it and certainly not enough to cause any serious damage to humans.

So based on this description, let’s go through the options one by one and see which option fits best. Starting with option A, which says that background radiation is any electrically neutral radiation. Well, we know that this is not true because background radiation can be any kind of ionizing radiation, which includes 𝛼, 𝛽, and 𝛾 radiation. Now, 𝛾 radiation is electrically neutral because it’s an electromagnetic wave. But 𝛼 radiation and 𝛽 radiation are not electrically neutral, and they do form some parts of background radiation. Therefore, option A is not the answer that we’re looking for.

Moving on to option B then. This one says that background radiation is low-level radiation from the surrounding environment, which is not due to the deliberate introduction of radiation sources. And this description does match what we said earlier about background radiation. Therefore, it looks like option B is the answer that we’re looking for.

Quickly looking at option C and D, starting with option C. This one says that background radiation is any low-energy electromagnetic radiation. But this is not true either, because like we said earlier background radiation can include 𝛼, 𝛽, and 𝛾 radiation. And 𝛼 and 𝛽 radiation is not electromagnetic radiation. In fact, an 𝛼 particle is the same thing as the nucleus of a helium atom. And a 𝛽 particle, or at least a 𝛽 minus particle, is an electron. And both of these are not low-energy electromagnetic radiation. And finally, even though 𝛾-rays are electromagnetic radiation, they most certainly are not low-energy electromagnetic radiation. In fact, they’re very high energy electromagnetic radiation. And hence option C is not what we’re looking for, either.

Finally, looking at option D, this one says that background radiation is any radiation from sources that have a half-life of less than one minute. Now, let’s recall that half-life is the amount of time taken for the activity, the radioactivity, of a particular sample of radioactive material to fall to half its initial value. In other words, if a substance has a half-life of less than one minute, then it takes less than one minute for half of that radioactive substance to have decayed away.

But then, if this were the case, then all of the radioactive isotopes causing background radiation would decay away very quickly and we’d have background radiation for a few minutes. But then it would disappear in a very short time scale. And this certainly does not happen. Background radiation is present constantly. Therefore, the answer to our question is that background radiation is a low-level radiation from the surrounding environment, which is not due to the deliberate introduction of radiation sources.

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