Radioactivity - Basics

 Radiation, atomic bomb, Chernobyl, Fukushima, contamination - these are the first terms that will come to mind when we hear the word "radioactivity". This topic evokes many emotions, mainly fear. When we hear that a radioactive cloud is approaching from Ukraine, we do not believe it, but some part of us is cautious and says: "Damn, what if that's true? If I ignore this information, just as did I ignore reports of a pandemic? In fact, I have no way to check if this is not nonsense, so maybe it is better to notify my loved ones for the sake of safety. " In this way, fake news spreads like lightning and the public begins to fear. People begin to ask another question: “If that's true, how do I protect myself? What should I do to be safe? " There is a high probability that you will be looking for the answers on the Internet. That's good. But it's also very bad.

Good, because the Internet is an invaluable source of knowledge that contains answers to all questions about protection against ionizing radiation, or "radioactivity". Very bad, because among the islets of genuine knowledge there is a furious ocean of pseudoscience, fake news, conspiracy theories, deliberate misinformation and popular opinion. So how do you separate truth from falsehood? Where to find reliable knowledge? For starters, I recommend the National Atomic Energy Agency, Central Institute for Labor Protection, Sanepid (for example, the Gorzów WSSE website) and scientific articles from research and academic institutions.

However, a problem arises - this knowledge is often provided in a hermetic and inaccessible manner. Instead of a thorough explanation of what ionizing radiation is and life advice on how to protect yourself against it, we receive a handful of dry facts, models and excerpts from the Atomic Law Act. While the professional website is like a medicine, we have a stream of online experts on everything who say that the best defense against radiation is consuming iodine. Most of us probably believe this myth, but the prophylactic drinking of Lugol's can lead to serious problems with the thyroid gland (iodine can actually protect us from ionizing radiation, but only in one, very specific case, and so the protection is very selective and limited only to area of ​​our thyroid gland - but I will discuss this topic in another article). I want to emphasize very clearly - learning from the internet can kill you. Therefore, you have to be careful where you get the knowledge.

First, start with the theoretical basics. I will present them as condensed as possible, providing only the information that is absolutely necessary from the point of view of health protection. In addition, descriptions of some physical phenomena will be provided in a simplified manner so that they can reach a wide audience, so I am asking all physicists and specialists to correct it.

Let's start with the very term "radiation" which is quite unfortunate because we have many types of radiation. The sun emits light, heat and ultraviolet radiation. The radiator emits thermal radiation. Light bulb - heat and light. The radiation that this article is about is called ionizing because it causes ionization of the medium, i.e. it knocks electrons out of atoms. Substances that are sources of ionizing radiation are called radioactive or radioactive.

There are several types of ionizing radiation, but the truth is that the average person only deals with two: X-rays and gamma rays (whose characteristics are almost identical, as is the protection against them). However, each type should be mentioned.

Alpha radiation is a stream of alpha particles, or helium nuclei, composed of two neutrons and two protons.

The range of this radiation in the air is about 10 cm, and in human tissue, 0.1 mm (for the energy of 10 MeV). This is a very small range. A simple piece of paper can stop them, but that doesn't mean alpha is harmless. Problems begin when a radioactive substance is swallowed or enters the lungs - then it becomes deadly (possibly this is how the former FSB agent Alexander Litvinenko was poisoned). However, the risk that you will ever come across a life-threatening alpha source is minimal (unless you swallow an americium-241 smoke detector. For safety, I advise you not to swallow smoke detectors 🙂

Beta radiation is a stream of electrons or positrons from the nuclei of atoms.

As with alpha radiation, the likelihood of a beta encounter is just as low. Beta radiation is more permeable than alpha. The 10 MeV beam penetrates the air to a distance of 4 meters, so you would have to be really close to the source to hurt yourself. Beta radiation shields are made of aluminum or organic glass. It is worth mentioning that the lead shield is not the best solution here because it generates secondary radiation, the so-called brake radiation.

Neutron radiation is a stream of free neutrons.

This radiation comes almost entirely from deliberate human activity. The likelihood of you encountering a source of neutron radiation in your life is practically zero. The best cover is a substance containing a lot of hydrogen, for example water, as well as polyethylene and paraffin.

In one sentence - the above types of radiation are so exotic that we will not deal with them. It is true that alpha and beta radiation hits your body at any moment, but these are negligible values. Virtually all of the radiation you come into contact with on a daily basis is:

Gamma radiation - electromagnetic radiation of extremely high frequency (above 10 exahertz) and quantum energy greater than 10 keV (this definition is not strict and is presented differently in the literature).

Gamma radiation can carry very high energies, it is extremely penetrating and ubiquitous. Every second that you read this text, you are bombarded with about half a million gamma quanta from rocks, soil, or even the walls of your apartment. To this should be added 150 quanta that come directly from outer space, as well as radiation that comes from ourselves, mainly from the decay of the potassium-40 isotope (about 4,000 decays per second). I do not include radioactive isotopes, mainly radon, which are inhaled with the air ... Gamma rays are so common that it is a miracle to find a place where there is none. I professionally measure the natural radiation of rock deposits in boreholes and only a few times in my life I managed to find pure limestone, which showed zero activity (which does not mean that the radiation was not there - the gamma detector was simply too weak to detect it) ).

If gamma rays are unfamiliar to you, then you know X rays, or X rays, which are of the same nature as gamma rays. The main difference between them lies in the place of their origin - X-rays are generated outside the nucleus of the atom, for example during a collision of an accelerated electron with matter, and gamma is generated by the nucleus itself, for example during radioactive decay. Since we are able to carry out controlled collisions of electrons with matter, we are also able to create an X-ray generator, i.e. an X-ray machine (the construction of an X-ray tube is actually very simple).

Since ionizing radiation is everywhere and bombards us every day, then how much radiation is that? What level is normal and what level is dangerous? How much radiation does a statistical Pole receive during a year? To answer this question, we first need to know:

How to measure ionizing radiation?

There are so many units related to radiation that you can write a thick book only on this subject - becquerel, kiur, gray, sievert, rad, rem or x-ray. It is similar with the types of radiation doses. At this point, there is no need to translate all the terms and we will focus only on the most important ones, i.e. on the effective (effective) dose expressed in sieverts [Sv] and on the effective (effective) dose, expressed in sieverts in a specific time unit. Since ionizing radiation occurs naturally and is ubiquitous, it has been referred to as background radiation and has different values ​​for different parts of the globe. For Poland, the background radiation is 2.4 mSv / year (milisiwert per year). According to the Atomic Law Act of September 11, 2019:

For the general population, the dose limit expressed as an effective (effective) dose is 1 mSv during a calendar year.

So an ordinary citizen may receive an additional 1 mSv / year. Is that a lot? No, that's very little, this standard is very strict. We can now answer the next question:

How much is that much radiation?

In many countries, background radiation is much higher than in Poland, even taking into account the additional dose prescribed by law. For example, for some regions of Finland, Brazil and China it is 7 mSv / year. An extreme case is the Iranian city of Ramsar, located on the Caspian Sea, where background radiation reaches even 131 mSv / year, which is over seventy times greater than the Polish norm. According to the Atomic Law Act, standards for workers exposed to ionizing radiation:

The dose limit for workers, expressed as an effective dose, is 20 mSv during a calendar year

Emergency situations and rescue operations are exceptional situations, where:

In an emergency exposure situation (…), every effort should be made to prevent a person participating in such activities from receiving an effective dose exceeding 100 mSv. A person participating in saving human life may receive an effective dose exceeding 100 mSv, however, every effort should be made not to receive an effective dose exceeding 500 mSv.

It is worth remembering these two values ​​- 100 mSv and 500 mSv and they should be treated as the limits of your own safety. What effective dose can kill us? It is assumed that a dose between 3 and 5 Sv will kill half of the population exposed to such radiation (death would occur within a month). 8 Sv is considered the lethal dose for 100% of the population.