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This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

Chernobyl nuclear power plant accident and Fukushima Daiichi nuclear power plant accident, so that many people have a strong fear and concern about radiation. So, how much radiation do we usually have at home? Do we need to worry about this? In fact, radiation is everywhere, but only ionizing radiation needs to be paid attention to.

By Louis Biarsson (Luis Villazon)

Translation | Li Shijie

Editor | Chen Qiang

The original article is published in Science focus 2023.10.

Simply put, radiation is energy that travels in the form of waves or particles. Visible light is radiation, infrared light produced by radiators is radiation, and so are radio waves emitted by wireless routers and mobile phones. This means that our room is always full of radiation.

Therefore, many people are worried that their homes are full of radiation, which will endanger their health. But the only thing you need to pay attention to is ionizing radiation-radiation that is powerful enough to knock electrons out of atoms. When a certain dose of radiation is reached (more than 100 millisieverts), ionizing radiation can lead to an increased risk of cancer. At very high doses (more than 1000 millisieverts), it can also cause radiation poisoning and burns.

What things in the home are radioactive? Cathode ray tube displays are display devices used in old televisions and computers, which produce low doses of ionized X-rays, but with the development of science and technology, almost all of them have been replaced by flat panel displays, which do not produce X-rays. Therefore, the only source of ionizing radiation left in our home is mainly things that contain a small amount of radioactive elements.

For example, bananas contain natural radioactive potassium-40. If you eat a banana, you will be exposed to 0.0001 millisieverts of radiation, which is roughly equivalent to the radiation dose you receive within 80 kilometers of a nuclear power plant. This dose is too small to have any effect on your health and can be ignored.

If a food is to be awarded the "maximum radiation award", it must be Brazil nuts. Brazil nuts are about five times more radioactive than bananas because Brazil nut trees have very deep roots and enrich the radioactive element radium from the soil. But eating two or three Brazil nuts a day is not harmful to your health.

When it comes to radioactive things, we have to mention cigarettes. We already know that smoking is harmful to health, but to make matters worse, the fertilizers used in tobacco cultivation also contain radioactive radium, lead and polonium, which makes a cigarette as radioactive as seven bananas.

If you have a smoke detector in your home, it will also produce ionizing radiation. The smoke detector contains traces of americium-241. This americium isotope produces radiation through alpha decay. However, this radiation can be completely blocked by a piece of paper, so it will never escape from the shell of the smoke detector. Unless you eat the smoke detector, it will not pose a threat to your health.

When it comes to eating, tableware is more closely related to eating. You may not know that some ceramic plates and cups made in the 1930s and 1970s used a special glaze mixed with radioactive uranium oxide. When you use these cutlery to eat or drink, you receive the equivalent of eating a banana every hour.

Location and altitude will affect the amount of radiation in the home. You may think that, from this point of view, there is no radiation in the home. However, it mainly depends on where you live to determine how radioactive your home is. If you live in the southwest of England, the biggest source of radiation in your home is the granite under the house. There is a certain amount of uranium in granite. Radium is produced when uranium decays, and radon is produced when radium decays. Radon can slowly escape into the air and release alpha rays. If the concentration of radon is too high, it may increase the risk of lung cancer.

There is a lot of granite in some parts of the UK, such as Cornwall. Residents in these areas receive a background radiation dose of about 7.8mSv per year, equivalent to eating 78000 bananas. Improving the ventilation system of the house, especially the ventilation condition of the basement, can prevent the radon concentration in the house from being too high, thus effectively reducing the harm of radon to the human body.

With the increase of altitude, the radiation dose will also increase. This is because at higher elevations, the thinner the air is, the easier it is for cosmic rays from space to penetrate the earth. For example, a day living in Denver (about 1600 meters above sea level) in the United States is equivalent to eating 12 bananas, while a transatlantic flight will give you about 0.04 millisieverts of radiation, which is equivalent to eating 400 bananas.

If you are lucky enough to be an astronaut living on the International Space Station, staying there for six months will expose you to an extra 80 millisieverts of radiation, the equivalent of eating 800000 bananas. This dose is not low, but it is not as harmful as eating so many bananas.

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