Radioactivity - Protection

 Is radiation dangerous? How to protect yourself from ionizing radiation? How to convert your cell into a dosimeter?

It's time to answer the next question:

Is radiation really that dangerous?

Yes, ionizing radiation is dangerous. However, the topic is much more complex than a simple yes or no answer. We remember from the previous article that gamma radiation is ubiquitous and can be as high as 131 mSv / year (without harm to human health). If so, does that mean that I can expose myself to 131 mSv unscathed because people in Iran live this way and are doing well? Not. The key factor here is time - the longer the dose is spread out over time, the better. This is best described with an example that will appeal to all of us - imagine you have ten liters of vodka. If someone told you to drink it in one day, you would be fatal. If you had a week for it, the case could end, if not with death, then at least with severe poisoning (although there are probably some players who will come out unscathed from such a challenge ...). However, if the dose of ten liters is distributed evenly throughout the year, it turns out that it will not make a big impression on our health (a small glass a day is produced). It is very similar to ionizing radiation. This is due to the fact that in the course of evolution the human body has created adaptive mechanisms thanks to which we can safely live in a radioactive environment, such as the Earth. Of course, within certain ranges. As a reminder, the lethal dose that will kill half the population (LD-50) is between 3 and 5 Sv. A dose of 8 Sv will kill 100% of the population, although the death will be postponed and take several weeks.

How does ionizing radiation damage the human body? Two main mechanisms can be distinguished - a gamma quantum can directly hit a DNA fragment, causing various types of damage - single or double strand breakage, damage to nitrogenous bases, etc. This may lead to cell mutation and, consequently, to neoplastic changes. The second mechanism is water radiolysis, i.e. the impact of a gamma quantum into a water molecule and the formation of a free radical, i.e. a chemically aggressive molecule containing an unpaired electron. It should be emphasized that both the breaking of DNA strands and the formation of free radicals also take place without radiation and the body has its own mechanisms to deal with these damages. Thanks to these mechanisms, we are able, to some extent, to cope with the effects of ionizing radiation.

There is a lot of evidence that exposure to low doses of radiation can be beneficial to health (a very good article on this topic is available on the website of the National Center for Nuclear Research (see here). On the other hand, we cannot forget about the existence of stochastic effects for which There is no threshold dose. In other words - any dose can be dangerous, which is due to regular statistics. It's a bit like playing the lottery - hitting a six is ​​extremely rare and by playing often you increase your chances, which does not mean that you will miss sixes if you only play once in your life.

Can a person feel the radiation?

Let me start provocatively - yes, you can feel the radiation as a skin burns. However, the moment you feel the radiation, you can be almost sure that you will die, but not right away (the effective dose for skin erythema is about 3 Sv). Except in the case of extremely high doses, the human body is unable to detect radiation. Ionizing radiation is invisible, inaudible, and odorless. It can kill you for hours without you even realizing it. This is one of the main reasons why it is so dangerous.

Since radiation is invisible and potentially dangerous, the next question will be:

How to safely handle radiation?

The answer is: reduce your exposure to a reasonable minimum. This is a universal principle that can be applied to any risk factor.

As Low As Reasonably Achievable

So in short ALARA. This principle is also known as ALARP - As Low As Reasonably Practicable, which is as little as possible. The key word is sensible (or practical).

Will the X-ray technician reduce the effective dose received by wearing a lead suit? Will decrease. Is it practical? Not.

This principle can be applied to any risk factor. In the era of a pandemic, will wearing a full gas mask with a carbon absorber reduce the risk of getting sick while shopping? Will decrease. Is it practical? Not.

Defining what that means reasonable or practical may be problematic. Among the radiation professionals, many procedures and instructions are defined as practical and sane. There are no such procedures for the general public, so you need to rely on your own common sense. To be on the safe side, stay away from radiation as far as possible, and when that is not possible when you are directly exposed to ionizing radiation, there are three factors that determine the dose you receive:

Time-Distance-Cover

Limit the exposure time, increase the distance from the radiation source, and increase the radiation-absorbing shield. This principle can be applied to any risk factor - radiation, biological and chemical agents, poisonous snakes, or angry wives/husbands - reduce time, increase distance, and protect yourself.

Time

There is no big philosophy here - the shorter the exposure time, the better for you. The dose obtained depends linearly on the exposure time. However, it is worth remembering that the biological effects are not linear - it is better to take 100 mSv in ten separate doses than in one cumulative one. The best analogy here is with sunbathing, or exposure to ultraviolet radiation. There is a difference when you spend one hour in the sun for ten days and ten hours in one day. As already mentioned, the body has its own defense mechanisms and is able to cope with small doses of radiation.

Distance

The radiation dose obtained is inversely proportional to the square of the distance. This means that if one meter from the source you get a dose of 1 Sv, then two meters from the source you will get 1/4 Sv, and at a distance of four meters, you will get 1/16 Sv. Each additional centimeter can literally save your life. Stay away from potential contamination. Not only radioactive.

Cover

The principle of building covers is simple - the denser the material, the better (note that this rule does not apply to beta radiation, for which lightweight materials such as aluminum or organic glass should be used). Gamma rays are extremely penetrating, which means they are very difficult to protect against. At home, it is not possible to build an outfit that would allow us to effectively protect against gamma, so we are forced to take shelter in our apartments. Are the materials used in construction a good shield against radiation? Quite good - concrete with a density of 2.3 g / cm3, 30 cm thick, attenuates ten times gamma radiation (with an energy of 1 MeV, for 2 MeV you need 38 cm). The 50 cm layer attenuates the radiation by a factor of 100. This is a decent result. The house provides basic protection in the event of radiological hazards, but it should be remembered that windows do not act as a barrier to gamma radiation. For this reason, the best protection is a basement, preferably with no windows, as deep as possible.

Time, distance, and shield are the basics of protection against ionizing radiation. Now that we know how to protect ourselves, it's time for the next question:

How do I know what the risk is?

Under normal conditions, with an efficiently operating civilization (access to electricity provided), the current radiological situation can be checked on the website of the Polish Atomic Energy Agency or on our website. In the case of a black scenario where Poland is subject to large-scale radioactive contamination and the energy system collapses, you have to rely on yourself. There is a high probability that government services will start informing the public using available means, i.e. in this case radio waves (you should have a battery-powered or crank-powered radio as standard equipment). However, if this channel of communication is not available, then you have to deal on your own. How? In the best variant, you have a device for measuring the level of radioactivity, i.e. a radiometer or a dosimeter (there is a difference between them), i.e. the Geiger counter famous in pop culture (there are much better radiometers).

However, if you do not have such a device, you can use your mobile phone in emergency situations. This method is not certified in any way, and the measurement itself is flawed, but thanks to this method you can approximately tell if the radiation is normal or if a nuclear disaster has just occurred, and you need to hide in a basement. The measurement mechanism is as follows - the camera matrix (CMOS) is sensitive to shocks of free electrons. Since a gamma quantum impact on matter creates free electrons, these can be detected by the matrix. If the matrix is ​​obscured from visible light, the number of electrons detected can be correlated with the dose rate.

There are several applications on the market that enable such measurement. Among the free applications for Android, GammaPix Lite should be mentioned, with the paid ones - Radioactivity Counter (cost $ 4.5).

Radioactivity Counter gives the dose value in greys per hour - for gamma radiation, one gray equal one sievert, so we can treat the indications of the application as if it were giving the value in millisieverts per hour.

Below you can see the extremely high radiation (10 sieverts per hour) recorded with a mobile phone when testing the Radioactivity Counter application:

These applications should not be treated as amateur dosimeters, but rather as an emergency method of measuring whether a nuclear disaster has just started. Then the question arises:

Is it worth buying a dosimeter (radiometer)?

If you were to ask this question to any radiological protection inspector, chances are he would kill you with a laugh and then tap his forehead. I understand this behavior a bit, but on the other hand, wouldn't the virologist's reaction be the same if you asked him a few months ago if it was worth stocking up on FFP2 masks? Nobody expected a global epidemic to break out, and few were prepared for it, including state services. Why stock up on food or disinfectants, since the likelihood of a pandemic is minimal ... Isn't it the same with radioactive contamination?

Returning to the question - the dosimeter is not a basic necessity, it is relatively expensive, and for a fraction of this price, you can buy a phone application that will be accurate enough to warn us of the danger. However, if you have excess cash, it is worth getting a radiometer/dosimeter. What's the difference between them? A radiometer is a device used to measure the dose of radiation (the spatial equivalent of a dose), and a dosimeter is used to measure the dose rate, i.e. a dose expressed in time. Traditional dosimeters (sometimes called passive) do not display any information and the data is read by a specialized worker. However, modern, electronic personal dosimeters perform the function of a radiometer and dosimeter, and also provide the cumulative value of the dose received or warn about exceeding a given radiation level.