London, Feb 12: Many people are frightened of radiation, thinking of it as an invisible, man-made and deadly force, and this fear often underpins opposition to nuclear power. In fact, most radiation is natural and life on Earth wouldn’t be possible without it.
In nuclear power and nuclear medicine we’ve simply harnessed radiation for our own use, just as we harness fire or the medical properties of plants, both of which also have the power to harm. Unlike some toxins found in nature, humans have evolved to live with exposure to low doses of radiation and only relatively high doses are harmful. A good analogy for this is paracetamol – one tablet can cure your headache, but if you take a whole box in one go it can kill you.
The Big Bang, nearly 14 billion years ago, generated radiation in the form of atoms known as primordial radionuclides (primordial meaning from the beginning of time). These now are part of everything in the universe. Some have very long physical half-lives, a measure of how long it takes for half of their radioactivity to decay away: for one radioactive form of thorium it is 14 billion years, for one of uranium 4.5 billion and one of potassium 1.3 billion.
Primordial radionuclides are still present in rocks, minerals and soils today. Their decay is a source of heat in the Earth’s interior, turning its molten iron core into a convecting dynamo that maintains a magnetic field strong enough to shield us from cosmic radiation which would otherwise eliminate life on Earth. Without this radioactivity, the Earth would have gradually cooled to become a dead, rocky globe with a cold, iron ball at the core and life would not exist.
Radiation from space interacts with elements in the Earth’s upper atmosphere and some surface minerals to produce new “cosmogenic” radionuclides including forms of hydrogen, carbon, aluminium and other well-known elements. Most decay quickly, except for one radioactive form of carbon whose 5,700-year half-life enables archaeologists to use it for radiocarbon dating.
Primordial and cosmogenic radionuclides are the source of most of the radiation that surrounds us. Radiation is taken up from the soil by plants and occurs in food such as bananas, beans, carrots, potatoes, peanuts and brazil nuts. Beer for instance contains a radioactive form of potassium, but only about a tenth of that found in carrot juice.
Radionuclides from food largely pass through our bodies but some remain for periods of time (their biological half-life is the time for our bodies to remove them). That same radioactive form of potassium emits high energy gamma rays as it decays which escape the human body, ensuring that we are all slightly radioactive.
Living with radioactivity
Historically, we have been oblivious to the presence of radioactivity in our environment but our bodies naturally evolved to live with it. Our cells have developed protective mechanisms that stimulate DNA repair in response to damage by radiation.
Natural radioactivity was first discovered by French scientist Henri Becquerel in 1896. The first artificial radioactive materials were produced by Marie and Pierre Curie in the 1930s, and have since been used in science, industry, agriculture and medicine.
For instance, radiation therapy is still one of the most important methods for treatment of cancer. To increase the potency of therapeutic radiation, researchers are currently trying to modify cancer cells to make them less able to repair themselves.
We use radioactive material for both diagnosis and treatment in “nuclear medicine”. Patients are injected with specific radionuclides depending on where in the body the treatment or diagnosis is needed. Radioiodine, for example, collects in the thyroid gland, whereas radium accumulates chiefly in the bones. The emitted radiation is used to diagnose cancerous tumours. Radionuclides are also used to treat cancers by targeting their emitted radiation on a tumour.
The most common medical radioisotope is 99mTc (technetium), which is used in 30 million procedures each year worldwide. Like many other medical isotopes, it is manmade, derived from a parent radionuclide that itself is created from fission of uranium in a nuclear reactor.
Radiation fear could boost fossil fuels
Despite the benefits that nuclear reactors offer us, people fear the radiation they create either due to nuclear waste, or accidents such as Chernobyl or Fukushima. But very few people have died due to nuclear power generation or accidents in comparison to other primary energy sources.
We worry that fear of radiation is harming climate mitigation strategies. For instance, Germany currently generates about a quarter of its electricity from coal, but considers nuclear dangerous and is closing down its remaining nuclear power stations.
But modern reactors create minimal waste. This waste, along with legacy wastes from old reactors, can be immobilised in cement and glass and disposed of deep underground. Radioactive waste also generates no carbon dioxide, unlike coal, gas or oil.
We now have the understanding to harness radiation safely and use it to our and our planet’s benefit. By fearing it too much and rejecting nuclear power as a primary energy source, we risk relying on fossil fuels for longer. This – not radiation – is what puts us and the planet in the greatest danger. (The Conversation)
(AGENCIES)
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