An introduction to nuclear radiation and its impacts on human health and Earth’s environment

Ron Gester, retired geologist & physician, 2023.

Earth is a nuclear planet … and nuclear energy is essential for our existence on Earth.

Without Earth's molten core, life as we know it would not exist. Earth is protected from extreme levels of cosmic and solar radiation by a geomagnetic field generated by the rotation of Earth’s molten core. It rotates because of a combination of convection, due to heat, and Earth's rotation. The heat is generated in part from the radioactive decay of uranium, thorium, and potassium isotopes. [Johnston, 2011] This heat also contributes to convection in the mantle which drives plate tectonics and continental drift. Nuclear energy is a natural and essential force on Earth. Nuclear fission reactors have occurred naturally in Earth’s geologic past. Rock formations in Oklo, Gabon, W. Africa reveal that self-sustaining nuclear reactions ran in these formations for hundreds of thousands of years starting about 1.7 billion years ago.

Nuclear radiation is everywhere. What is it?

Nuclear radiation is a form of energy released from the decay of the nuclei of certain kinds of atoms. It is the same whether it is naturally occurring or man-made. It can be described as waves or particles and is part of the electromagnetic spectrum that includes light and radio waves. Ionizing radiation is radiation that has enough energy to remove electrons from their orbits, creating ions. Examples of ionizing radiation are high-level ultraviolet light, X-rays, and gamma rays. Natural uranium emits gamma rays. Uranium is not a scarce resource. As a result of its very wide range of geochemical behavior, it is present in most soil, rocks, and water. [Deffeyes, 1980]

Low-dose ionizing radiation is safe. How do we know this? Research in biology & epidemiology.

Life on Earth evolved in a radioactive environment. This background radiation comes from space and Earth. Life has adapted to it to survive. This is true in different ways for the many threats to life including heat, cold, sunshine, and oxygen.

  • Every cell in our body is struck by radiation and damaged, including breaks in our DNA, multiple times every day. Our bodies have evolved mechanisms for repairing the damage. [Lindahl, 2015]
  • Earth's natural radioactive environment varies with location due to differences in altitude and geology. Cancer rates have not correlated with these differences. [Dobrzynski, 2015]
  • Ionizing radiation has been studied and used in medical care for more than 100 years. Low doses are used for diagnosis (e.g. chest X-rays & CT scans). Higher dose radiation and radioisotopes produced in nuclear reactors are used to treat various types of cancer.
  • Epidemiological studies of people accidentally exposed to ionizing radiation (e.g. Nagasaki & Chornobyl) confirm that while high doses can be fatal, low doses are not. [UNSCEAR, 2008]

“The dose makes the poison” ~Paracelsus, 1538 German-Swiss physician, father of toxicology.

For example, oxygen and sunlight at low doses or levels are essential for our health, but at high doses, they can be lethal. Similarly, taking two adult aspirin will reduce inflammation, pain, and fever. However, taking one hundred can be life-threatening. The effect of ionizing radiation also varies with dose and at low doses, it may be essential to good health. [Dobrzynski, 2015] Why is this uncertain? Research focused on the effects of low-dose radiation is difficult because it is a challenge to build a laboratory where there is zero radiation. (e.g. Therefore, the question of what happens in our cells if there is zero radiation has not yet been definitively answered. Many scientists believe that low-dose ionizing radiation stimulates the “damage control biosystem” (see below) and its absence may be harmful. [Cuttler, 2007] It’s a logical conclusion.

Radiobiology: What happens when we are exposed to ionizing radiation?

We each have ~ 50 trillion cells and each cell suffers “more than 10,000 DNA lesions per day”. [Carusillo, 2020] The damage comes from many sources including ionizing radiation and reactive oxygen species (ROS). The latter are produced by the mitochondria in our cells. Oxidative stress can occur when there is an imbalance of free radicals (including ROS) and antioxidants in the body. It is one of the reasons antioxidant supplements became popular. There is little evidence they are effective. (HSPH 2023)

Our DNA is damaged continuously: How do we survive? The “damage control biosystem”.

Relatively recent research has revealed the role of DNA repair. [Lindahl, 2015: Nobel Prize in Chemistry] Numerous adaptive response mechanisms have been identified. [Chatterjee, 2017] They include:

  • five major DNA repair pathways: base excision repair, nucleotide excision repair, mismatch repair, homologous recombination, and non-homologous end joining
  • enhanced production in the cell’s nucleus of repair enzymes for damaged DNA,
  • slowed mitosis (cell division) that permits these enzymes to accomplish their function,
  • induced apoptosis that destroys cells that escape the repair,
  • enhanced production of antioxidant enzymes that lower the rate of damage to DNA and other molecules from ROS.

Radiation level guidelines & observations: How is radiation measured?

 Ionizing radiation is commonly measured in Sieverts (Sv). One Sv is the dose equivalent to 1 Joule of energy per kilogram of human tissue. One Sv is a large dose, so doses are often expressed as milli-sieverts (mSv). There are 1,000 mSv in one Sievert. The effect of a dose also varies with duration. The following doses are in mSv per year except when noted otherwise such as Acute which means the dose is received all at once. Safe dose? In the past, before biological research revealed that cells have systems to repair the damage, 0 mSv or “no dose” was the logical “safe dose” for critics and regulators. Now? It is a subject of debate.

Radioactive news headlines: Putting them in perspective. What is a safe dose?

mSv / year (except when noted otherwise)

 0         Maximum safe dose according to antinuclear “experts” in the past. [e.g. H Caldicott, J Goffman]

.005     Acute dose from a dental x-ray [Rad. Patient Info, 2023]

.21       Acute dose from a mammogram [Rad. Patient Info, 2023]

.88       Fukushima, Namie Town (close to reactor) 3/2020, ~9 yrs. after accident [Okutsu, 2020]

1          NRC (Nuclear Regulatory Commission) regulation: max dose allowed to the public [HPS, 2016]

3.1       USA average natural background radiation [DOE, 2017]

7.7       Acute dose from CT scan of the abdomen and pelvis [Rad. Patient Info, 2023]

50        NRC regulation: maximum dose allowed for radiation workers in the US [HPS, 2016]

100      Acute dose below which there is no consistent evidence of radiation-caused cancer [DOE, 2017]

175      Guarapari, Brazil, popular monazite sand beach, background radiation [Wiki. Guarapari, 2023]

260      Ramsar, Iran, natural background radiation [DOE, 2017]

300      Dose below which there is no consistent evidence of radiation-caused cancer [DOE, 2017]

306      Fukushima, Namie Town (close to reactor) 6/2011, ~4 mos. after accident [WNA, 2023]

500      Chornobyl 530,000 workers; 20 - 500 mSv from ‘86 -‘90; 0 rad. deaths ’86 -‘23 [UNSCEAR, 2008]

500      Acute dose that causes decreased blood cell counts, not fatal [DOE, 2017]

1,000   Acute dose causes radiation sickness, usually not lethal if treated [DOE, 2017]

5,000   Acute dose that is lethal 50% of the time within 30 days [DOE, 2017]

10,000 Acute dose that is usually fatal [DOE, 2017]

16,000 Chornobyl 134 workers; Acute dose of 800 – 16,000 mSv; 28 rad. deaths [UNSCEAR, 2008]

Radiation protection: How can we limit radiation exposure? What about the waste?

 While natural background radiation is generally low and not dangerous, it is useful to be aware of the easy ways to decrease exposure if you are worried. [EPA, 2023] There are 3 ways: 1) limit exposure time, 2) increase the distance from the source of radiation, and 3) shield either the source or the recipient. The first two, are relatively self-explanatory.

The third, shielding, depends on the type of radiation:

  • Alpha particles (from uranium) can’t penetrate even skin or paper, but they can be inhaled. Shield with a good surgical mask.
  • Beta particles (tritium) can penetrate paper and skin but not travel far. Shield with a disposable gown.
  • Neutrons (from uranium in nuclear power plants) penetrate most substances but can be contained by large quantities of water. The best response is to limit time and proximity.
  • X-rays and gamma rays are electromagnetic radiation. They are stopped by lead aprons or leaded glass.

Current radioactive waste management is to submerge it in water for 10 years before transferring it to a welded steel dry cask containing an inert gas and enclosing the steel cask in a concrete exterior. Other options include recycling used nuclear fuel and storing waste deep underground. Both have been done. All energy sources generate waste. “Nuclear power is the only large-scale energy-producing technology that takes full responsibility for all its waste and fully costs this into the product.” [WNA, 2022]

Nuclear energy: There are other low-carbon sources of energy. Why should we choose nuclear?

Compared to all other common energy sources, nuclear energy has three significant advantages that are not widely appreciated: high capacity factor [DOE, 2020], long service life [Statista, 2023], and high fuel energy density [Layton, 2008]. When nuclear energy is compared per kWh to other low-carbon sources over the same service life (60 – 80 years for nuclear), these three advantages reveal that nuclear has the lowest cost, greatest reliability, and least consumption of natural resources (e.g. land, cement, steel). [Carrara, 2020] “Nuclear energy has been quietly powering America with clean, carbon-free electricity for the last 60 years”. It has generated about 20% of America’s electricity since 1990 and currently provides about half of the carbon-free electricity. [DOE, 2021]

 It is time to appreciate and actively promote nuclear energy on our planet.



Carrara, S. (2020) European Commission, Joint Research Center, Raw materials demand for wind and solar PV technologies in the transition towards a decarbonized energy system

Carusillo, A (2020). & Mussolino, C. Journal Cells, DNA Damage: From Threat to Treatment. Paragraph 2, “Each human cell experiences more than 10,000 DNA lesions per day”

Chatterjee, N (2017) & Walker, Environ Mol. Mutagen. Mechanisms of DNA damage, repair, and mutagenesis,

Cuttler, J (2007) Dose-Response, Health Effects of Low-Level Radiation: When Will We Acknowledge the Reality,

Deffeyes, K (1980), & MacGregor, I., Scientific American, World Uranium Resources. 242.1: 66-76.

Dobrzynski (2015) Dose-Response, Cancer Mortality Among People Living in Areas with Various Levels of Natural Background Radiation.

DOE (2017) Office of Environment, Health, Safety and Security: Information Brief, The DOE Ionizing Radiation Dose Ranges Chart; See page 6 figure 6.

DOE (2020) What is Generation Capacity? See graph titled: US Capacity Factor by Energy Source, 2021,

DOE (2021) 5 fast facts about nuclear energy

EPA (2023) Protecting Yourself from Radiation; Time, Distance and Shielding.

HPS (2016) Health Physics Society website, Regulatory Dose Limits, Annual Radiation Dose Limits

HSPH (2023) Harvard School of Public Health, The Nutrition Source: What are antioxidants?

Johnston (2011) Physics World - Research update, Radioactive decay accounts for half of Earth’s heat

Layton, B. (2008) International Journal of Green Energy. A Comparison of Energy Densities of Prevalent Energy Sources in Units of Joules Per Cubic Meter.

Lindahl (2015) Lindahl, T., Modrich, P., & Sancar, A., Nobel Prize in Chemistry, “For mechanistic studies of DNA repair.”

Meshik (2009) Scientific American, The Workings of an Ancient Nuclear Reactor,

Okutsu (2020) Nikkei Asia News, Former Fukushima ghost town stirs with new business 9 years on. Namie, Fukushima Prefecture (See paragraph 7) 0.1 micro-sieverts/hr equals 0.88 milli-sieverts/yr.

Rad. Patient Info (2023) Radiology Info for Patient website; See tables for Effective radiation dose in adults for various procedures with comparison to background radiation,

Statista (2023) Lifetime of energy sources and power plants worldwide by type (in years) (2020)

UNSCEAR (2008) United Nations: Scientific Committee on the Effects of Atomic Radiation; Assessment of the Radiation Effects from the Chornobyl Nuclear Reactor Accident, Summary: ‘88 –‘08, see Health Effects section

Wikipedia: Guarapari: Radioactivity (2023)

WNA (2022) See: Information Library: Radioactive Waste Management: first sentence;

WNA (2023) See Information Library: Fukushima Daiichi: Radiation exposure and fallout beyond the plant site: first paragraph: “At the end of July (4 mos. after the accident) the highest level measured within 30km radius (of the accident site) was 0.84 mSv/day in Namie” = 306 mSv/yr.

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