Nuclear physics

Nuclear Physics, From the Atomic Nucleus to Energy, Medicine, and Abundance

Nuclear physics is the study of the atomic nucleus: what it is made of, what holds it together, and what happens when it changes. For anyone interested in futurism and abundance, it is one of the most consequential fields in science. The same physics that powers the Sun also runs low-carbon power plants, keeps spacecraft alive beyond the reach of sunlight, lets doctors see disease inside the body, and dates the human past. Understanding the nucleus helps separate realistic paths toward plentiful energy from experimental ones.

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The nucleus, protons, and neutrons

Every atom has a tiny, dense core called the nucleus, made of protons and neutrons, surrounded by electrons. Protons carry a positive electric charge, electrons a negative charge, and neutrons no charge at all. The number of protons fixes the element; atoms with different neutron counts are isotopes, such as carbon-12 and carbon-14.

The energy stored in the nucleus is far larger, per kilogram, than the chemical energy that fuels, foods, and batteries rely on, which is the starting point for everything else on this page.

The strong force and binding energy

Protons repel one another electrically, so something stronger must hold the nucleus together. That something is the strong nuclear force, which attracts protons and neutrons to each other at very short range. It is the strongest of the fundamental forces but acts only across distances about the size of a nucleus.

When protons and neutrons bind into a nucleus, the finished nucleus weighs slightly less than its separate parts. The missing mass has been released as energy, following Einstein's relation between mass and energy. This is binding energy; divided by the number of particles, it measures how tightly a nucleus is held together.

Plotted against mass number, binding energy per nucleon rises through the light elements, peaks near iron and nickel, and declines toward uranium. Iron-56 is often described as the most tightly bound nucleus. A 1995 analysis in the American Journal of Physics showed that this common belief is slightly off: both iron-58 and nickel-62 are more strongly bound than iron-56, and nickel-62 has the highest mean binding energy of all. The emphasis on iron-56 may originate from studies of how stars make elements.

The shape of this curve explains two technologies at once. Joining very light nuclei moves them up the curve and releases energy (fusion). Splitting very heavy nuclei also moves the pieces up the curve and releases energy (fission). Nuclei near the iron and nickel peak have no further energy to give by either route.

Radioactive decay and half-life

Many nuclei are unstable. They change on their own into more stable forms by emitting radiation, a process called radioactive decay. The main types are:

• Alpha decay: the nucleus emits an alpha particle made of two protons and two neutrons. Alpha particles cannot penetrate skin but can harm tissue if inhaled or swallowed.
• Beta decay: the nucleus emits a fast, small, charged particle. Tritium and carbon-14 are beta emitters.
• Gamma emission: the nucleus releases a high-energy photon, often along with alpha or beta decay. Gamma rays can pass through the whole body.

The time it takes for half of a radioactive sample to decay is its half-life. Each half-life is a fixed property of its isotope, which makes decay useful as a clock, a medical tool, and a long-lived power source.

Fission and fusion

In fission, a neutron strikes a heavy nucleus such as uranium-235 and splits it, releasing heat, radiation, and more neutrons. Those neutrons can split further nuclei, producing a chain reaction. Reactors control this chain reaction to make heat for steam turbines.

In fusion, light nuclei combine into a heavier one. Fusion is the energy source of the Sun and other stars. The U.S. Energy Information Administration describes its commercial viability as not yet clear because fusion reactions are difficult to control.

Why nuclear physics matters for abundance

Energy density: one pellet against a tonne of coal

A single uranium fuel pellet, about the size of a fingertip, contains as much energy as a tonne of coal. A 1,000 megawatt pressurized water reactor needs about 27 tonnes of uranium per year, roughly 18 million pellets, while a coal station of the same size needs more than two and a half million tonnes of coal. For a post-scarcity future, less fuel means less mining, less freight, and reliable power where hauling bulk fuel is impractical, from remote towns to off-world settlements.

Fission reactors and small modular reactors

Nuclear power plants have supplied about 20 percent of annual U.S. electricity generation since 1990. A newer direction is the small modular reactor (SMR). The U.S. Department of Energy describes advanced SMRs ranging from tens of megawatts up to hundreds of megawatts, usable for electricity, industrial process heat, or desalination. Intended advantages include smaller footprints, reduced capital investment, and incremental capacity additions. The Department expected light water SMRs under Nuclear Regulatory Commission review to be deployed in the late 2020s to early 2030s.

Fusion ignition at the National Ignition Facility

On December 5, 2022, the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory became the first controlled fusion experiment to reach ignition, also called scientific energy breakeven. Its 192 lasers delivered 2.05 megajoules of energy to a small fuel target, which produced 3.15 megajoules of fusion energy. The comparison is with laser energy delivered to the target, not with the total energy needed to run the facility. Livermore itself stated that many advances in science and technology are still needed before inertial fusion can affordably power homes and businesses.

Medical isotopes and PET imaging

Technetium-99m is used in roughly 85 percent of medical imaging procedures worldwide. Its half-life of about six hours means the isotope cannot be stockpiled. Hospitals draw it from generators containing its parent, molybdenum-99, which has a half-life of about 66 hours. In the United States, about 40,000 imaging procedures per day use technetium-99m, about half of world demand. A vital product that decays on the shelf must be made continuously.

Positron emission tomography (PET) uses a different kind of decay. A tracer emits positrons, which meet electrons in the body and annihilate, producing two gamma ray photons that travel in opposite directions. A radiolabeled form of glucose called FDG lights up rapidly dividing cancer cells, and combined PET/CT scanners have become the primary imaging tool for staging most cancers worldwide.

Radiocarbon dating

Cosmic rays create carbon-14 in the atmosphere, and living things absorb it while they are alive. After death, the carbon-14 decays with a half-life of about 5,730 years. Willard Libby proposed dating organic material this way in 1946 and received the 1960 Nobel Prize in Chemistry for it. The method now reliably dates materials as old as 50,000 years. It showed that the last North American ice sheet receded 10,000 to 12,000 years ago, not 25,000 as geologists had estimated.

Nuclear power in spacecraft

Radioisotope power systems, which include radioisotope thermoelectric generators (RTGs), turn the heat from the natural decay of plutonium-238 into electricity. NASA has flown 24 missions with these systems since the Apollo era, and they power both Voyager probes, New Horizons, and the Curiosity and Perseverance rovers on Mars. It is the clearest existing example of nuclear decay as a dependable utility beyond Earth.

Nucleosynthesis: the elements as a nuclear inheritance

Stars are fusion reactors. Main sequence stars fuse hydrogen into helium, and massive stars go on to build carbon, oxygen, neon, magnesium, and finally iron. Fusing iron into heavier elements would consume energy rather than release it, so the core collapses and the star can explode as a supernova, spreading its elements into space for future stars and planets. The iron in human blood and the metals that future asteroid miners hope to extract are products of nuclear physics inside stars.

Limits and risks

Waste. Spent reactor fuel is highly radioactive and can remain dangerous for thousands of years. It is cooled in water pools and often moved later to dry casks. The United States does not have a permanent disposal facility for high-level nuclear waste. The World Nuclear Association estimates that about 97 percent of used fuel could be recycled into fresh fuel.

Proliferation. The materials and skills used for civilian nuclear work overlap with those used for weapons. Medical isotope production, for example, historically relied on highly enriched uranium. The U.S. National Nuclear Security Administration has funded efforts to convert production to low enriched uranium and other methods specifically to reduce proliferation risk.

Accidents. The World Nuclear Association, an industry body, counts three significant accidents at commercial power plants. At Three Mile Island in 1979 the reactor was severely damaged but radiation was contained. At Chernobyl in 1986 a steam explosion and fire destroyed the reactor, killing two people initially and 28 more from radiation poisoning within three months, with significant health and environmental consequences. At Fukushima Daiichi in 2011 a tsunami caused a loss of cooling that wrecked three reactors and released some radioactivity.

Cost overruns. A study of five decades of U.S. data found that nuclear plant costs repeatedly exceeded projections and that later plants were more expensive than earlier ones. Soft factors such as labor supervision contributed over half of the cost rise from 1976 to 1987, and labor productivity in recent plants was up to 13 times lower than industry expectations. Nuclear abundance depends on solving construction, not only physics.

Learning projects and resources

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• Nuclear physics
• Nuclear engineering basics

Readings

• Wikipedia:Nuclear physics

Discussion questions, essay ideas, and learning related AI prompt ideas

• Explain why both fission of uranium and fusion of hydrogen release energy, using the binding energy curve and the position of nickel-62 near its peak.
• Compare the fuel, mining, and transport needs of a 1,000 megawatt nuclear plant with a coal plant of the same size, and discuss what that difference implies for remote communities.
• Write an essay on whether small modular reactors could change the economics of nuclear power, drawing on the evidence about past cost overruns.
• Describe what the National Ignition Facility achieved in December 2022 and list the engineering steps still needed before fusion could supply electricity to a grid.
• Explain why a six hour half-life makes technetium-99m both medically useful and difficult to supply, and propose ways to make that supply chain more resilient.
• Discuss why radioisotope power systems are used on missions to the outer planets and what role they could play in long-term human settlement beyond Earth.
• Weigh the risks of nuclear waste, proliferation, and accidents against the benefits of low-carbon energy and medical isotopes, and argue for a policy you consider balanced.

See also

• Physics
• Quantum physics
• Chemistry
• Nuclear engineering
• Energy
• Electricity
• Energy costs and abundance
• Geothermal drilling and energy abundance
• Medicine
• Astronomy
• Solar astronomy
• Space travel