The Atomic Age, also known as the Atomic Era, is a phrase typically used to delineate the period of history following the detonation of the first atomic bomb, Trinity, on July 16, 1945. Although nuclear chain reactions had been hypothesised in 1933 and the first artificial self-sustaining nuclear chain reaction (Chicago Pile-1) took place in December 1942, the Trinity test and the ensuing bombing of Hiroshima, Japan represented the first large scale use of nuclear technology and ushered in profound changes in socio-political thinking and the course of technology development. Atomic power was seen to be the epitome of progress and modernity.

Most of the smoke detectors work either by optical detection (photoelectric) or by physical process (ionisation), while others use both detection methods to increase the sensitivity to smoke. An ionisation smoke detector uses a radioisotope such as Americium-241 to produce ionisation in air. When a difference due to smoke is detected, an alarm is generated.

Presently the nuclear fission of elements in the actinide series of the periodic table produces the vast majority of nuclear energy in the direct service of humankind. More than 60 years after the first attempts, commercial fusion power production remains unlikely before 2050. United States of America has the highest number of functional nuclear reactors in the world, with the number currently standing at 104.

Magnetic Resonance Imaging (MRI), Nuclear Magnetic Resonance Imaging (NMRI), or Magnetic Resonance Tomography (MRT) is a medical imaging technique used in radiology to visualise internal structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body. MRI can create more detailed images of the human body than are possible with X-rays. An MRI scanner is a device in which the patient lies within a large, powerful magnet where the magnetic field is used to align the magnetisation of some atomic nuclei in the body, and radio frequency magnetic fields are applied to systematically alter the alignment of this magnetisation.

On June 27, 1954, the USSR's Obninsk Nuclear Power Plant became the world's first nuclear power plant to generate electricity for a power grid, and produced around 5 megawatts of electric power.

According to last estimates released by IAEA in 2011, around 10% of world’s electricity generation comes from nuclear power plants. Annual generation of nuclear power has been on a slight downward trend since 2007, decreasing 1.8% in 2009 to 2558 TWh with nuclear power meeting 13–14% of the world's electricity demand. One factor in the nuclear power percentage decrease since 2007 has been the prolonged shutdown of large reactors at the Kashiwazaki-Kariwa Nuclear Power Plant in Japan following the Niigata-Chuetsu-Oki earthquake.

Radiocarbon dating (or simply carbon dating) is a radiometric dating technique that uses the decay of carbon-14 to estimate the age of organic materials, such as wood and leather, up to about 58,000 to 62,000 years. Carbon dating was presented to the world by Willard Libby in 1949, for which he was awarded the Nobel Prize in Chemistry.

In 1963, all nuclear and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater or in outer space. 

In 1896, Henri Becquerel was investigating phosphorescence in uranium salts when he discovered a new phenomenon which came to be called radioactivity. He, Pierre Curie and Marie Curie began investigating the phenomenon. In the process, they isolated the element radium, which is highly radioactive. They discovered that radioactive materials produce intense, penetrating rays of three distinct sorts, which they labeled alpha, beta and gamma after the Greek letters. Some of these kinds of radiations could pass through ordinary matter, and all of them could be harmful in large amounts.

The three forms of radiation that Becquerel and the Curies discovered are also more fully understood. Alpha decay is when a nucleus releases an alpha particle, which is two protons and two neutrons, equivalent to a helium nucleus. Beta decay is the release of a beta particle, a high energy electron. Gamma decay releases gamma rays, which unlike alpha and beta radiation are not matter but electromagnetic radiations of very high frequency, and therefore energy.

In nuclear physics, nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at a very high speed and join to form a new type of atomic nucleus. For example, the energy that the sun emits into space is produced by nuclear reactions that happen in its core due to the collision of hydrogen nuclei and the formation of helium nucleus.

One isotope of Uranium, namely Uranium-235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope Uranium-238. The latter accounts for more than 99% of the weight of natural Uranium. Alternatively, the element Plutonium possesses an isotope that is sufficiently unstable for this process to be usable. Plutonium does not occur naturally, so it must be manufactured in a nuclear reactor.

A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature, and its surroundings. The concept is important in nuclear weapon design.

Nuclear power is the use of exothermic nuclear processes to generate useful heat and electricity. The term includes the following heat producing processes: nuclear fission, nuclear decay and nuclear fusion.

A radionuclide or a radioactive nuclide is an atom with an unstable nucleus characterised by excess energy available to be imparted either to a newly created radiation particle within the nucleus or via internal conversion. Radionuclides are often referred to by chemists and physicists as radioactive isotopes or radioisotopes.