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Radioactive decay

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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).[1]

Contents

Properties

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.[2]

Product

Decay chain of radioactive elements into lead.

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.'[2]

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.

Rate

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).

Decay types

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
Composition Alpha particle (helium nucleus) Beta particle (electron) High-energy electromagnetic radiation
Symbol 42He or α 0 − 1e or β γ
Charge 2+ 1- 0
Mass 4 1/1837 0
Penetrating power Low Moderate Very high

[3]

Alpha

Alpha, beta, and gamma radiation have differing abilities to penetrate substances. Alpha particles have low power and can be shielded by a sheet of paper or by human skin. Some beta particles can be stopped by human skin, but some need a thicker shield (like wood) to stop them. Gamma rays are the most penetrating of the three types of radiation, requiring a shield at least as thick as a concrete wall.[2]

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.[4]

For example, examine the following chemical equation. Superscripts represents the mass numbers and subscripts represents the atomic numbers.

^{238}_{ 92}\mathrm{U} \to ^{234}_{90}\mathrm{Th} + ^{4}_{2}\mathrm{He} (α emission)

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.[5]

Beta

There are 3 types of Beta decay: electron emission, electron capture, and positron emission. [5] 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.[6]

^{14}_{6}\mathrm{C} \to ^{14}_{7}\mathrm{N} + ^{ 0}_{-1}e (β emission)

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.

Gamma

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.

^{230}_{ 90}\mathrm{Th} \to ^{226}_{ 88}\mathrm{Ra} + ^{4}_{2}\mathrm{He} + \gamma

Since gamma rays do not have any mass, it does not affect the atomic number or mass number of an atom. [7]

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.[8]

He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper.[9] 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.[10] 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.[9]

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.[11] 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.[10]

Accelerated nuclear decay

Main article: Accelerated decay

In 1970 through 1971, Robert Gentry provided two lines of evidence that, he suspected, supported the idea of an unknown form of radiation: giant radioactive halos and unique Pb isotope ratios.

“Previously unreported lead isotope ratios, that is, values for the lead-206/lead-207 ratio ranging from about 20 to 60, primarily radiogenic in origin but unsupported by uranium decay, have been determined in the inclusions of certain polonium halos by means of ion microprobe techniques. Evidence for radiogenic lead-208 unsupported by thorium decay may also be inferred from the existence of a composite polonium halo type with rings from the radioactive precursors of lead-208. Several new dwarf halo sizes, seem to indicate the existence of unknown, very low-energy alpha-emitters. Furthermore, the three-ring "X halo" also provides evidence for an unknown series of genetically related alpha-emitters with energies in the range from 3 to 7 million electron volts.”- Robert Gentry [12]
“A new group of giant radioactive halos has been found with radii in excess of anything previously discovered. Since alternate explanations for these giant halos are inconclusive at present, the possibility is considered that they originate with unknown alpha radioactivity, either from isomers of known elements or from superheavy elements.”-Robert Gentry [13]

Since then, the RATE Group developed definitive evidence that what Gentry had discovered was not evidence of a new type of radiation, but of radioactive acceleration.

Dr. Walt Brown followed up on this and made the most radical proposal to date: that all radioactive elements and isotopes formed on the earth itself,[14] during the severe earthquakes attendant upon the global flood.

Uses

Geiger counter used to measure radioactive emissions from a sample.

Describe the uses of radioactive decay here.

Nuclear Powerplants

Age Dating

Radioactive Tracers

Cancer Treatment

Sterilizing

Smoke Detectors

Genetic Studies

Some references:

References

  1. Radiation and Radioactivity by the U.S. Environmental Protection Agency
  2. 2.0 2.1 2.2 Why Are Some Atoms Radioactive? by the U.S. Environmental Protection Agency.
  3. Antony Wilbraham, et. al. Chemistry. Upper Saddle River, New Jersey: Prentice Hall, 2008. p801
  4. Alpha decay by Wikipedia
  5. 5.0 5.1 Radioactive Decay The Bodner Group. Bodner Research Web.
  6. Beta Decay Physics 2000. by the Department of Physics. University of Colorado at Boulder.
  7. Gamma ray by Wikipedia
  8. Discovery of Radioactivity by Dr. V B Kamble. Vigyan Prasar Science Portal
  9. 9.0 9.1 The Discovery of Radioactivity by the Lawrence Berkeley National Laboratory
  10. 10.0 10.1 The Discovery of Radioactivity by Duke University Department of Chemistry.
  11. The Discovery Of Radioactivity: The Dawn of the Nuclear Age by Fran Slowiczek, Ed.D and Pamela M. Peters, Ph.D., Access Excellence.
  12. Gentry, R.V. 1971. Radiohalos: Some Unique Pb Isotope Ratios and Unknown Alpha Radioactivity. Science 173, 727.
  13. Gentry, R.V. 1970. Giant Radioactive Halos: Indicators of Unknown Alpha-Radioactivity? Science 169, 670.
  14. The Origin of Earth's Radioactivity by Dr. Walt Brown, Center for Scientific Creation, Online Edition

External links

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See Also


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