NUCLEAR RADIATION - Nuclear radiation refers to the particles and photons emitted during reactions that involve the nucleus of an atom. Nuclear radiation is also known as ionizing radiation or ionising radiation. The particles emitted by nuclear reactions are sufficiently energetic that they can remove electrons from atoms and molecules and ionize them. Nuclear radiation includes gamma rays, x-rays, and the more energetic portion of the electromagnetic spectrum. Ionizing subatomic particles released by nuclear reactions include alpha particles, beta particles, neutrons, muons, mesons, positrons, and cosmic rays. During the fission of U-235 the nuclear radiation that is released contains neutrons and gamma ray photons. Radiation and radioactivity are two easily confused concepts. Just remember, a substance does not need to be radioactive to emit radiation. Radiation is the emission and propagation of energy in the form of waves, rays or particles. Radiation includes emanation of any portion of the electromagnetic spectrum, plus it includes the release of particles. Examples include: A burning candle emits radiation in the form of heat and light. The Sun emits radiation in the form of light, heat, and particles. Uranium-238 decaying into Thorium-234 emits radiation in the form of alpha particles. Electrons dropping from one energy state to a lower state emit radiation in the form of a photon.

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Nuclear Radiation Definition

By Anne Marie Helmenstine, Ph.D.

Nuclear radiation refers to the particles and photons emitted during reactions that involve the nucleus of an atom.

Nuclear radiation is also known as ionizing radiation or ionising radiation (depending on the country).

The particles emitted by nuclear reactions are sufficiently energetic that they can remove electrons from atoms and molecules and ionize them.

Nuclear radiation includes gamma rays, x-rays, and the more energetic portion of the electromagnetic spectrum.

Ionizing subatomic particles released by nuclear reactions include alpha particles, beta particles, neutrons, muons, mesons, positrons, and cosmic rays.

Nuclear Radiation Example

During the fission of U-235 the nuclear radiation that is released contains neutrons and gamma ray photons.

Radiation and radioactivity are two easily confused concepts. Just remember, a substance does not need to be radioactive to emit radiation.

Let's look at the definition of radiation and see how it differs from radioactivity.

Radiation Definition

Radiation is the emission and propagation of energy in the form of waves, rays or particles. There are three main types of radiation:

·       Non-ionizing radiation: This is the release of energy from the lower-energy region of the electromagnetic spectrum. Sources of non-ionizing radiation include light, radio, microwaves, infrared (heat), and ultraviolet light.

·       Ionizing radiation: This is radiation with sufficient energy to remove an electron from an atomic orbital, forming an ion. Ionizing radiation includes x-ray, gamma rays, alpha particles, and beta particles.

·       Neutrons: Neutrons are particles found in the atomic nucleus. When they break away from the nucleus, they have energy and act as radiation.

Examples of Radiation

Radiation includes emanation of any portion of the electromagnetic spectrum, plus it includes the release of particles. Examples include:

·       A burning candle emits radiation in the form of heat and light.

·       The Sun emits radiation in the form of light, heat, and particles.

·       Uranium-238 decaying into Thorium-234 emits radiation in the form of alpha particles.

·       Electrons dropping from one energy state to a lower state emit radiation in the form of a photon.

Difference Between Radiation and Radioactivity

Radiation is the release of energy, whether it takes the form of waves or particles.

Radioactivity refers to the decay or splitting of an atomic nucleus. A radioactive material releases radiation when it decays.

Examples of decay include alpha decay, beta decay, gamma decay, neutron release, and spontaneous fission.

All radioactive isotopes release radiation, but not all radiation comes from radioactivity.

Anne Marie Helmenstine, Ph.D.

Chemistry Expert

Education

Ph.D., Biomedical Sciences, University of Tennessee at Knoxville

B.A., Physics and Mathematics, Hastings College

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/definition-of-nuclear-radiation-605423

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CHERNOBYL - A Timeline of The Worst Nuclear Accident in History - In 1986, Chernobyl had four working reactors, with two new ones under construction. The newest of the four, Reactor No. 4, contained 1,600 radioactive uranium-235 fuel rods. Because U-235 is unstable, its atoms spontaneously release neutrons, which hit other U-235 nuclei, causing them to release neutrons. This is what is called a chain reaction. The byproduct of a chain reaction is the release of enormous quantities of heat and energy, and this heat is what's used to turn water into steam, which drives a turbine, that generates electricity. To keep a chain reaction from running away with itself and becoming a nuclear bomb, control rods containing a neutron absorbing substance are inserted between the fuel rods. Reactor No. 4 had 211 control rods made of the element boron. If you raise the control rods, the chain reaction accelerates, if you lower the control rods, the chain reaction slows.

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Chernobyl

A Timeline of The Worst Nuclear Accident in History

By  Marcia Wendorf

33 years ago, a series of missteps caused the worst nuclear accident in history, and its effects are still being felt to this day.

Located 65 miles north of Kiev, Ukraine, the V.I. Lenin Nuclear Power Station at Chernobyl was a model of Soviet engineering. Its four RBMK nuclear reactors produced enough electricity for 30 million homes and businesses.

The RBMK reactor is a class of graphite-moderated nuclear power reactor that was designed and built by the Soviet Union.

Certain aspects of the design contributed to the Chernobyl disaster, and there were calls for the reactors to be decommissioned.

However, the reactors were redesigned, and as of 2019, ten are still in operation.

1,600 Radioactive U-235 Fuel Rods

In 1986, Chernobyl had four working reactors, with two new ones under construction. The newest of the four, Reactor No. 4, contained 1,600 radioactive uranium-235 fuel rods.

Because U-235 is unstable, its atoms spontaneously release neutrons, which hit other U-235 nuclei, causing them to release neutrons. This is what is called a chain reaction.

The byproduct of a chain reaction is the release of enormous quantities of heat and energy, and this heat is what's used to turn water into steam, which drives a turbine, that generates electricity.

To keep a chain reaction from running away with itself and becoming a nuclear bomb, control rods containing a neutron absorbing substance are inserted between the fuel rods.

Reactor No. 4 had 211 control rods made of the element boron. If you raise the control rods, the chain reaction accelerates, if you lower the control rods, the chain reaction slows.

Friday, April 26, 1986, 11:45 p.m.

176 workers were coming in for their shifts from the neighboring town of Pripyat.

Built in 1970 as a company town for the power station, Pripyat had a population of 50,000, and enjoyed many of the luxuries denied to other Soviet citizens, such as well stocked supermarkets, good schools, and plentiful sports facilities.

This night involved the continuation of a test that was begun twelve hours earlier. It was a test of the plant's ability to keep Reactor No. 4 cool in the event of a power failure.

Whether the plant’s still-spinning turbines could produce enough electricity to keep the coolant pumps running during the brief gap before the emergency generators would kick in.

To perform the test, they would have to shut the reactor down, and by the time the night shift arrived, the reactor was operating at 50% power.

"The odds of a meltdown are one in 10,000 years." -- Vitali Sklyarov, Minister of Power and Electrification of Ukraine

Saturday, April 26, 1986 00:28 a.m.

The night shift foreman, Alexander Akimov, began arguing with Chernobyl’s Deputy Chief Engineer, Anatoly Dyatlov, over how low the amount of electrical power the reactor was generating should be taken.

Akimov cited a manual which stated that it should not be less than 700 megawatts, while Dyatlov insisted that 200 megawatts was be safe. Since Dyatlov outranked him, Akimov had to agree.

1:19 a.m.

The Reactor Control Engineer, Leonid Toptunov, blocked the automatic shutdown of the reactor due to a low water level, and raised the reactor's power up to 7 percent by removing all but six of the control rods. The reactor was now growing unstable.

1:23:40 a.m.

Readings showed the reactor's temperature had climbed to 4,650 C, almost as hot as the surface of the sun.

An engineer who had been on a catwalk above the reactor ran into the control room, shouting that the fuel rod caps were jumping in and out of their sockets. These caps weigh 350kg (772 lb) each.

Alarmed, Akimov pressed a button to reinsert the control rods, but instead of dropping their full seven meters, they stopped at between two and 2.5 meters.

1:23:45 a.m.

The reactor reached 120 times its full power, and its radioactive fuel disintegrated. There was a long, low, almost-human sounding moan, then an explosion lifted the 1,000-ton concrete shield that was above the reactor and wedged it at an angle.

This allowed air to reach the reactor, and the oxygen in the air started a fire in the reactor's graphite. The air also caused the metal in the fuel tubes to react with the water in the reactor to produce hydrogen gas.

Hydrogen gas is highly flammable, and it exploded, blasting debris into the air and onto the roof of the neighboring Reactor No. 3.

In a study commissioned by the U.S. government on the Chernobyl disaster, Richard Wilson of Harvard University described this second explosion as a small nuclear explosion.

01:26:03 a.m.

"Call everybody, everybody" -- Chernobyl Dispatch

The first fire alarm came in to Paramilitary Fire Station Number Two, based on the grounds of the power plant. The firemen scrambled to Reactor No. 4 and climbed up onto its ruined roof.

Afraid to use water because of the exposed electrical cables, the firemen threw sand and used their canvas hoses to beat out the flames.

In Reactor No. 4's control room, two trainees, Aleksandr Kudryavtsev and Viktor Proskuryakov, were sent to assess the damage.

They made it to the reactor hall where they observed the 1,000-ton Upper Biological Shield jammed at an angle in the reactor shaft, and blue and red flames raging in the reactor itself.

Both Kudryavtsev's and Proskuryakov's bodies immediately darkened with what is known as "nuclear tan" as they received a fatal dose of radiation.

2:50 a.m.

Workers inside the plant had accounted for all the staff with the exception of Valery Khodemchuk. At the time of the accident, Khodemchuk had been in the main circulating pump room, which was close to the explosion. Unbeknown to his coworkers, he had been vaporized by the explosion.

Chernobyl's doctor, Valentyn Belokon, who had been treating injured workers realized that the they were suffering from radiation poisoning. He called the hospital in Pripyat and requested potassium iodide tablets. Potassium iodide blocks radioactive iodine from being absorbed by the thyroid gland.

7:30 a.m.

Akimov and Toptunov entered Reactor No. 4 in an attempt to bring water into the ruined reactor. This would cost them their lives. Akimov died on May 11th, having said that his conscience hurt more than his injuries, and Toptunov died three days later.

8:00 p.m.

Inhabitants of Pripyat gathered on a railway bridge that had a view of the nuclear power plant to view the beautiful flames of all colors caused by the burning graphite.

A breeze from the power plant swept over them, carrying a radiation dose of 500 Roentgens. No one standing on the bridge survived, and it is called the "bridge of death".

Sunday, April 27, 1986 10:00 a.m.

The first of what will become almost 1,800 helicopter flights above the reactor began. The heliocopters dropped sand, lead, clay, and neutron absorbing boron onto the burning reactor, but practically none of the neutron absorbing materials reached the core.

Due to the radiation, the helicopter crews were aware that theirs was most likely a suicide mission, but they went anyway.

2:00 p.m.

The authorities began an evacuation of the city of Pripyat. Via loudspeaker, they told people to take enough food and clothing for three days, and to leave their pets behind. In total, almost 350,000 people were evacuated, and they would never return. The pets left behind were shot.

Monday, April 28, 1986

On his way out of the plant after a shift, a worker at the Forsmark Nuclear Power Plant in Sweden went through a radiation detector, and the detector went off.

It was quickly determined that a cloud of radioactive gas had drifted across all of Scandinavia, Germany and Czechoslovakia. Pharmacies in Denmark quickly sold out of potassium iodide tablets.

Tuesday April 29, 1986

A U.S. reconnaissance satellite showed the roof Reactor No. 4 blown off, and the glowing mass inside still smoking.

In an attempt to protect them from thyroid cancer, Polish authorities began distributing potassium iodine tablets to children living in the northeastern part of that country.

Friday May 2, 1986

There were two floors of pools containing water directly beneath Reactor No. 4, plus the basement was flooded with water from ruptured pipes and that used by the firefighters. The smoldering graphite, nuclear fuel and other materials had formed a mass called corium, which is a radioactive version of lava.

The mass was burning at a temperature of more than 1,200 degrees C., and if it melted through the reactor hall floor and into the pools of water, a steam explosion would hurl the mass into the air and would eject even more radiactive material.

Three engineers volunteered to drain the water from the pools - Alexei Ananenko, Valeri Bezpalov and, Boris Baranov. Their mission was a success, but all three died from radiation sickness.

The China Syndrome

The molten mass still posed a threat if it melted down to groundwater below the reactor building. This is the so-called "China Syndrome".

At first, workers tried freezing the ground beneath the reactor by injecting it with liquid nitrogen. Then, they filled the reactor room with concrete.

In the "China Syndrome", the core components of a nuclear reactor melt down, burning through the containment vessel and the building housing the reactor, then they burn through the Earth's crust and body until reaching the opposite side of the planet, which in the U.S. is colloquially referred to as China.

In reality, a core couldn't penetrate the several-kilometer thickness of the Earth's crust, and it certainly couldn't travel back upwards against the pull of gravity. Also, China is not the antipode of any landmass in North America.

May 6, 1986

Authorities closed the schools in the cities of Gomel and Kiev, and they began relocating children. Kiev radio warned people not to eat leafy vegetables, and to stay indoors as much as possible.

December 14, 1986

Work started on a concrete "sarcophagus" that would completely encase Reactor No. 4, and protect the environment from radiation for what was hoped to be at least 30 years. 300,000 tons of concrete and 6,000 tons of metal were used to build the sarcophagus.

September 17, 2007

After realizing that the sarcophagus might not be sufficient, work began on a new confinement structure designed by a French consortium called Novark.

That structure was comprised of a 150 by 257-meter arch that would be slid into place. Construction costs were estimated at €432 million euros, with a project time of five years.

The Aftermath

In the immediate aftermath of Chernobyl, a total of 31 firemen and plant workers died. Some of their bodies were so radioactive, they had to be buried in lead coffins.

A report by the World Health Organization estimated that 600,000 people within the Soviet Union were exposed to high levels of radiation, and of those, 4,000 would die. Those who lived near the Chernobyl site have reported increased instances of thyroid cancer, and they have an increased risk of developing leukemia.

Anatoly Dyatlov and the director of the Chernobyl plant, Viktor Bryukhanov, were sentenced to ten years each in prison for their roles in the disaster.

The "Liquidators"

Scores of people stepped up to contain the disaster, and they came to be called the "Liquidators". They include:

* Yuri Korneev, Boris Stolyarchuk and Alexander Yuvchenko who are the last surviving members of the Reactor No. 4 night shift

* The firefighters who immediately responded to the reactor accident

* The Civil Defense Troops of the Soviet Armed Forces who removed contaminated materials and deactivated the reactor itself

* Internal Troops and the police who provided security, access control and population evacuation

* Military and civil medical and sanitation personnel

* The Soviet Air Force and civil aviation units who performed critical helicopter-assisted operations on the reactor building, air transportation and aerial radiation monitoring

* A team of coal miners who built a protective foundation to prevent radioactivity from entering the aquifer below the reactor

* Construction professionals

* Media and performing artists who risked their lives to document the disaster and to provide on-site entertainment for the liquidators

* The photographers Igor Kostin and Volodymyr Shevchenko who took photos in the immediate aftermath, including photos of Liquidators conducting highly-hazardous manual tasks.

700 Million Years

The Chernobyl accident is one of only two nuclear energy accidents that is classified as a "Level 7 Event," the highest classification. 

The other is 2011's Fukushima disaster in Japan.

At the lowest level of Reactor 4 lies the famous "elephant's foot", a several-meter wide mass of corium that is still giving off lethal amounts of radiation.

The half-life of radioactive elements is defined as the amount of time it takes for the radioactivity to fall to half its original value. The half-life of U-235 is 700 million years.

Marcia Wendorf

Author

Marcia is a former high school math teacher, technical writer, author, and programmer. In much the same way as high school students in the U.S. are taught "defensive driving", Marcia practices "defensive living": staying on top of worldwide news about science, government policies, finance, infrastructure, and medical issues. An outlier, Marcia is always "sniffing the wind" for the latest trends and directions, and keeping her readers abreast of these developments.

https://interestingengineering.com/chernobyl-a-timeline-of-the-worst-nuclear-accident-in-history

Corium

`` Containment structure

The elephant's foot 

Exclusion zone 

Liquidator medals

Pripyat

Reactor No. 4 roof collapsed

Reactor No. 4 burning core

Reactor No. 4 schematic Source

Reactor No. 4

RADIOACTIVITY - The decomposition process of unstable atomic nuclei to form nuclei with higher stability is called radioactivity. The energy and particles which are released during the decomposition process are called radiation. When unstable nuclei decompose in nature, the process is referred to as natural radioactivity. When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity.

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Radioactivity

What Is Radioactivity? What is Radiation?

Quick Review of Radioactivity

by Anne Marie Helmenstine, Ph.D. 

Unstable atomic nuclei will spontaneously decompose to form nuclei with higher stability. The decomposition process is called radioactivity.

The energy and particles which are released during the decomposition process are called radiation.

When unstable nuclei decompose in nature, the process is referred to as natural radioactivity.

When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity.

There are three major types of natural radioactivity:

Alpha Radiation

Alpha radiation consists of a stream of positively charged particles, called alpha particles, which have an atomic mass of 4 and a charge of +2 (a helium nucleus).

When an alpha particle is ejected from a nucleus, the mass number of the nucleus decreases by four units and the atomic number decreases by two units.

For example:

²³⁸₉₂U → ⁴₂He + ²³⁴₉₀^Th

The helium nucleus is the alpha particle.

Beta Radiation

Beta radiation is a stream of electrons, called beta particles.

When a beta particle is ejected, a neutron in the nucleus is converted to a proton, so the mass number of the nucleus is unchanged, but the atomic number increases by one unit.

For example:

²³⁴₉₀ → ⁰_-1e + ²³⁴₉₁Pa

The electron is the beta particle.

Gamma Radiation

Gamma rays are high-energy photons with a very short wavelength (0.0005 to 0.1 nm). The emission of gamma radiation results from an energy change within the atomic nucleus.

Gamma emission changes neither the atomic number nor the atomic mass. Alpha and beta emission are often accompanied by gamma emission, as an excited nucleus drops to a lower and more stable energy state.

Alpha, beta, and gamma radiation also accompany induced radioactivity. 

Radioactive isotopes are prepared in the lab using bombardment reactions to convert a stable nucleus into one which is radioactive.

Positron (a particle with the same mass as an electron, but a charge of +1 instead of -1) emission isn't observed in natural radioactivity, but it is a common mode of decay in induced radioactivity.

Bombardment reactions can be used to produce very heavy elements, including many which don't occur in nature.

Anne Marie Helmenstine, Ph.D.

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/what-is-radioactivity-604312