Watch The Physics, Not Just The Screen, While Watching Chernobyl

While watching HBO’s five-part Chernobyl miniseries, I realized that there is real physics behind every scene the screen shows us. “3.6 roentgen, not great, not terrible” is not just a line of dialogue; once you understand that moment, the whole weight of the series feels different. I had wanted to gather these ideas in my mind and write about them for a while.

In this article, I will try to explain the radiation terms used in the series together with their scientific background.

Three Different Types Of Radiation, Three Different Dangers

There are three main types of radiation we encounter in nuclear reactions: alpha, beta and gamma. Understanding how differently they behave compared to one another allows you to read many scenes in the series with a completely different eye.

Alpha radiation is a type of radiation that does not contain photons, in other words light. We call the high-energy helium nucleus that appears during a nuclear reaction alpha radiation. Because it has a large mass, it travels only a very short distance in air before stopping; even the clothes you are wearing can stop it. But there is a trap here: although protection from alpha radiation may seem easy, if you come into direct contact with the source or inhale it, you can receive 10 to 20 times more biological damage than you would from the same amount of beta or gamma radiation.

 

Beta radiation, on the other hand, consists of high-energy electrons. Electrons are much smaller particles compared to protons, so they can travel farther in air. A few millimeters of aluminum are enough to stop this radiation; doors and windows also provide partial protection. But I want to especially note this: if you use a heavy metal while stopping beta radiation, for example if you choose iron or lead, this time you face another problem. When a fast-moving electron suddenly stops, it can emit X-rays through braking radiation. In other words, the plate you hold up for protection, if chosen incorrectly, can unknowingly expose you to another type of radiation.

Using heavy metal against beta radiation can create unnecessary X-ray exposure instead of protecting you.

Gamma radiation is what most people know as “radiation.” Because it consists of massless photons, it is genuinely difficult to stop. Thick lead plates, dense concrete or high-density materials such as barium sulfate concrete are needed. You may wonder why it passes through DNA so easily: DNA is made of light elements such as carbon, hydrogen, nitrogen and oxygen. Lead has 82 protons, iron has 26. The proton numbers of the elements that make up DNA are expressed in single digits. Gamma rays can pass through light elements with less interaction; in heavy and dense materials, however, they are attenuated much more strongly.

The thickness needed to halve gamma radiation changes depending on the material used. Concrete is widely used in practice because it is the most common building material, but it takes up a lot of space. Iron can provide more attenuation with a thinner layer, but it is heavy. Lead is one of the most efficient options because of its density; it is soft, cheap and therefore frequently used in radiation shielding.

The Physics Behind The Scenes In The Series

In the second episode, the reason the doctor says “take off the clothes” is exactly this alpha and beta radiation issue. Because the clothes carry radioactive particles, they turn into a threat source themselves. Those people should have been stripped and washed long before they arrived at the hospital. Showering and changing clothes immediately after being contaminated with radioactive particles can significantly reduce the amount of radiation received.

In the fourth episode, the reason the workers on the roof are told “don’t look down” is also beta radiation. The eyes are especially fragile against this kind of radiation. The burns on the face of the man who climbs onto the reactor and looks down at the end of the first episode can also be read in this context. This is called a beta burn, and the mechanism is explained exactly through this kind of superficial but severe tissue damage.

“3.6 Roentgen, Not Great, Not Terrible”

This is the famous moment in the early episodes when the authorities deceive themselves. What is being discussed here should roughly be understood as a radiation level of 3.6 roentgen per hour. The problem is this: in reality, the team on site had devices that could measure higher levels, but one was buried in the building wreckage and the other was malfunctioning. At that moment, no one could truly believe that the reactor had completely exploded; therefore, they could not accept that the radiation could be that high.

Akimov’s team tried to pump water into the reactor until morning without wearing protective equipment, and within a few weeks, many of them, including Akimov, died.

One of the units used to measure radiation dose is the sievert. To give a reference point, 80 millisieverts can be thought of as close to the dose level an astronaut might receive after spending about 6 months on the space station. The average dose received by people evacuated from the Fukushima area remained below even that. NASA’s current astronaut career limit is set at 600 millisieverts. In the range of 1 to 2 sieverts, symptoms such as nausea, headache and fatigue can appear; the death rate is generally low, but it is still a level that must be taken seriously. In the range of 2 to 6 sieverts, symptoms can become severe within hours and the risk of death without treatment rises sharply. Above 6 sieverts, even with treatment, the risk of death rises to a very serious level.

It is estimated that those who died within a few weeks after Chernobyl were exposed to approximately 6 sieverts or more of radiation.

Metallic Taste And Radioactive Iodine

It is no coincidence that characters in the first episodes mention a metallic taste in their mouths. This is one of the details that makes us feel that there is a very high amount of radioactive material in the air. One of the most important of these substances was radioactive iodine-131. Since the thyroid gland actively accumulates iodine, radioactive iodine-131 can also increase the risk of thyroid cancer.

This is where potassium iodide tablets come into play. When taken at the right time under the instruction of authorized health officials, potassium iodide can fill the thyroid gland with normal iodine and reduce the accumulation of radioactive iodine. But this is not something to take randomly; timing, dosage and necessity matter.

In addition to this, a large amount of cesium-137 was released into the air. This radioactive fallout settles into the soil, is absorbed by plants and continues its effect for years through the food chain. This is exactly why crops are collected with excavators in the series. Scraping away and removing the top few centimeters of soil, then applying potassium fertilizer to the remaining soil, can partially limit the contamination.

Strontium-90 can also be absorbed by plants in a similar way. As a precaution against this, lime and calcium-based fertilizer are added to the soil; this way, the element preferred by the plant becomes calcium rather than strontium.

Cesium-137 and strontium-90 have a half-life of about 30 years. So if there are 10 units of these substances in an area, 30 years later, 5 units still remain active. Another 30 years must pass for half of that remaining amount to lose its effect. The nuclear fallout that settled on the forests and fields of the Black Sea region during those years worked through exactly this mechanism.

I watched Chernobyl and many scenes stayed in my mind; but after learning these terms, the series gained a completely different meaning. The attention the screenwriters and production team paid to scientific details is truly impressive. Maybe after reading this article, you may want to watch it again; this time by looking not at the scene, but at the physics behind it.