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Radioactive decay (or radioactivity) is the property of some atoms that causes them to spontaneously give off energy as particles or rays. Radioactive atoms emit ionizing radiation when they decay, meaning they have enough energy to break chemical bonds in molecules or remove tightly bound electrons from atoms, thus creating charged molecules or atoms (ions).
Radioactive atoms are unstable (known radionuclides). An atom is unstable (radioactive) if the forces among the particles that make up the nucleus are unbalanced--if the nucleus has an excess of internal energy. The instability of a radionuclide's nucleus may result from an excess of either neutrons or protons. An unstable nucleus will continually vibrate and contort and, sooner or later, attempt to reach stability by some combination of means:
- Ejecting neutrons, and protons
- Converting one to the other with the ejection of a beta particle or positron
- Releasing the additional energy by photon (i.e., gamma ray) emission.
Radioactive decay occurs when the unstable nucleus emits radiation (disintegrates). The radionuclide is thereby transformed to different nuclides (often called the daughter nuclide). It will continue to decay until the forces in the nucleus are balanced. For example, as a radionuclide decays, it will become a different isotope of the same element if the number of neutrons changes and a different element altogether if the number of protons changes.
Often, when a radionuclide decays, the decay product (the new nuclide) is also radioactive. This is true for most naturally occurring radioactive materials. In order to become stable, these materials must go through many steps, becoming a series of different nuclides and giving off energy as particles or rays at each step. The series of transformations that a given radionuclide will undergo, as well as the kind of radiation it emits, are characteristic of the radionuclide. This is called a 'decay chain.'
The radionuclide will undergo decay if there is a group of particles with a lower total mass that can be reached by decay or by nuclear fission (nucleus splits into smaller nuclei). All elements having an atomic number higher than 83 (the atomic number of bismuth) are radioactive. In addition, a number of elements having lower atomic numbers do have naturally occurring radioactive isotopes. Nuclear physicists have also made two synthetic elements having atomic numbers less than 83 to fill two gaps in the periodic table; both of these are radioactive
Every radioactive element or isotope decays at its own rate. The most common published statistic on the rate of decay of any radionuclide is the half-life. This is the hypothetical amount of time that must pass for half of the element or isotope to decay to its next daughter nuclide. Under normal circumstances, an isotope's half-life does not change, nor has any nuclear physicist ever produced a change in any isotope's half-life. However, the RATE Group has developed clear and convincing evidence that the half-lives of all then-naturally-occurring radioactive elements was accelerated greatly at the time of the Global Flood--and furthermore, this change might have triggered that event. (See: Accelerated decay).
Radio nuclides of different types can be involved in several different reactions that produce radiant energy. The three main types of ionizing radiation are alpha, beta, and gamma.
1.Alpha decay- Two protons and two neutrons emitted from nucleus
2.Beta decay- A neutron emits an electron and an antineutrino and becomes a proton
3.Gamma decay- Excited nucleus releases a high-energy photon
4.Positron emission- A proton emits a positron and a neutrino and becomes a neutrino
5.Internal conversion- Excited nucleus transfers energy to an orbiting electron and ejects it
6.Proton emission- A proton is ejected from nucleus
7.Neutron emission- A neutron is ejected from nucleus
8.Electron capture- A proton combines with an orbiting electron, emits a neutrino and becomes a neutron
9.Spontaneous fission- Nucleus disintegrates into two or more random smaller nuclei and other particles
10.Cluster decay- Nucleus emits a certain type of smaller nucleus that are larger than an alpha particle
11.Double-beta decay- two neutrons emit two electrons and two antineutrons become two protons
|Property||Alpha radiation||Beta radiation||Gamma radiation|
|Symbol||42He or α||0 − 1e or β||γ|
|Penetrating power||Low||Moderate||Very high|
Alpha radiation are helium nuclei that have been emitted from a radioactive source. The Alpha particle includes two protons and two neutrons and has a 2+ charge. An alpha particle can be written as 42He or as α in nuclear equations. The atomic number of the daughter atom is reduced by 2 and its mass number is lower by 4 when an atom loses an alpha particle.
For example, examine the following chemical equation. Superscripts represents the mass numbers and subscripts represents the atomic numbers.
The sum of the atomic masses of Thorium and alpha particle is equal to that of Uranium. As are the sums of the atomic numbers.
There are 3 types of Beta decay: electron emission, electron capture, and positron emission.  During electron emission, a neutron changes into a proton with the loss of an electron. For example, 31H becomes 32He with the loss of 0-1e.
A beta particle can be written as 0-1e or β in nuclear equations. The superscript 0 shows that electron has very small mass compared to proton. Since its subscript is -1, the electron has negative charge.
Since Carbon-14 emits a beta particle, the nitrogen-14 atom has the same atomic mass number (both of their superscripts are same), but its atomic number is increased by 1. It means that it contains one more proton and one fewer neutron.
A gamma ray is a high-energy photon emitted by a radioisotope. Sometimes, nuclei emit gamma rays with alpha or beta particles during radioactive decay as you can see in the following equation
Since gamma rays do not have any mass, it does not affect the atomic number or mass number of an atom. 
Types of Radiation:
Alpha Particles Alpha particles can be shielded by a sheet of paper or by human skin. However, if radionuclides that emit alpha particles are inhaled, ingested, or enter your body through a cut in your skin, they can be very harmful.
Beta Particles Beta particles cannot be stopped by a sheet of paper. Some beta particles can be stopped by human skin, but some need a thicker shield (like wood) to stop them. Just like alpha particles, beta particles can also cause serious damage to your health if they enter your body. For example, if ingested, some radionuclides that emit beta particles might be absorbed into your bones and cause damage.
Gamma and X-Rays Gamma rays are the most penetrating of the three types of radiation listed here. Gamma rays usually accompany beta, and some alpha rays. Gamma rays will penetrate paper, skin, wood, and other substances. To protect yourself from gamma rays, you need a shield at least as thick as a concrete wall. This type of radiation causes severe damage to your internal organs. (X-rays fall into this category, but they are less penetrating than gamma rays.)
History of discovery
Radioactivity was first discovered by accident in 1896 by a French scientist, Henri Becquerel. He was experimenting with fluorescent and phosphorescent materials to help understand the properties of x-rays and their ability to expose photographic film, which had been discovered in 1895 by Wilhelm Roentgen. Upon seeing x-ray exposed film, he immediately thought of putting some phosphorescent rocks on photographic paper to see if it would darken the film in the same way.
He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper. As Becquerel had anticipated, the phosphorescent salts had produced an image on the film. He theorized that the uranium absorbed the sun’s energy and then emitted it as x-rays. His theories were proven false when it became overcast in Paris putting off further experiments for a couple of days. He placed the photographic plates and the uranium salt in a drawer and for some unknown reason, decided to develop the photographic plates anyway. He was surprised to find a strong and clear image exposed onto the film, proving that the uranium emitted radiation without an external source of energy such as the sun. During this fortuitous sequence of events Becquerel had discovered radioactivity.
Marie Curie, who was one of Becquerel's students and her husband Pierre, continued to study radiation while working in Becquerel's lab. While testing an ore of uranium (pitchblende), for its ability to turn air into a conductor of electricity, she discovered that a much more active element than uranium must exist within the ore. She named this new element polonium, and coined the term radioactivity to describe the process. Henri Becquerel, Marie and Pierre Curie jointly received the Nobel Prize in physics in 1903 for their discovery of radioactivity and their other contributions in this area
Beneficial Uses of Radiation
Radioactive materials also provide substantial economic benefits. Worldwide, nuclear applications in industry alone including measurement gauges, smoke detectors and sterilization of medical supplie account for more than $40 billion each year.
Benefits of Man-Made
Radiation In the 20th century, mankind learned to use radiation to improve the quality of life. The development of nuclear technology is one of the most significant achievements of the 20th century, according to the National Academy of Engineering. Today, people use nuclear technology in nearly every field and aspect of life from medicine to manufacturing and construction, to powering common household items, to
producing electricity for one of every five U.S. homes and businesses.
Here are some of the many ways radiation benefits us all:
Medicine. According to the Society of Nuclear Medicine,
5,000 nuclear medicine centers in the United States perform nearly 18 million nuclear medicine procedures each year. These procedures prolong and improve the quality of people’s lives. Radioisotopes also are used in 100 million laboratory tests on body fluid and tissue specimens. Today, approximately 500,000 cancer patients in the United States receive radiation treatment at some point in their therapy. Radioisotopes and X-rays aid physicians in diagnosing and treating scores of other diseases.
Nuclear medicine can evaluate the functional performance of various organs. It can do that because different organs use different specific elements more than others. For example, the thyroid uses iodine, bones take up phosphorus and muscles use a lot of potassium. In nuclear medicine, tiny amounts of a radioactive form of these elements are introduced into a patient’s body. The “radioisotopes” are picked up by specific organs, enabling a special camera to take a picture of how that organ is functioning in striking detail. For example:
Myocardial perfusion imaging maps blood flow to the heart, allowing physicians to see whether a patient has heart disease and to determine the most effective course of treatment.
Bone scans can detect the spread of cancer six to 18 months earlier than X-rays.
Kidney scans are much more sensitive than X-rays or ultrasounds in fully evaluating kidney function.
Imaging with radioactive technetium-99m can help diagnose bone infections at the earliest possible stage.
Laboratory techniques using radioactivity can detect underactive thyroids in newborn babies, making prompt treatment possible and saving many children from mental retardation.
In higher doses, radioisotopes also help treat disease. When former President George H.W. Bush and Mrs. Bush suffered from Graves’ disease, a thyroid condition, they were cured by drinking a form of radioactive
iodine that concentrates naturally in the thyroid and destroys in the diseased portion. This treatment is so successful that it virtually has replaced thyroid urgery.
Radioactive iodine’s widespread use in therapy for thyroid cancer results in a lower recurrence rate than drug therapy and voids potentially fatal side effects, such as the destruction of bone marrow.