Talk:Radioactivity

a sub-set of radiation for the special case of radiation emitted from unstable nuclei. Hence, section 2 "Sources of Radiation" on the Radioactivity page should be removed and replaced by an of the varieties of radioactive decay routes of various unstable nuclei. You will notice that the information in section 2 "Sources of Radiation" duplicates information on the Radiation page where that information belongs.

I propose making changes accordingly to the Radioactivity page as I get time, if I hear no compelling counter arguments. Rednblu 06:53, 16 Aug 2003 (UTC)

Currently the two articles overlap significantly. Perhaps the two articles should simply be merged? --Andrew 08:45, Apr 26, 2004 (UTC)

There is now the article radioactive contamination. The material in these three articles should be rearranged. I suggest the following subdivision:

Radioactivity: the process whereby atoms decay, producing radiation. What kinds of radiation. Nothing about its effects.
Radiation: Various sorts of radiation; major section for non-ionizing radiation (which may just refer to other articles). Effects, dangers, etc. for external and internal radiation.
Radioactive contamination: The problem of radioactive elements loose in the environment; uptake, half-life, etc.

Comments? --Andrew 18:31, Apr 27, 2004 (UTC)

No objections, so rewrite process begun. See old version below. --Andrew 04:18, May 6, 2004 (UTC)

Making intro easier to understand

As this might be for a lot of people with no education in physics the first article they read about atomic nuclei I thought it was a good idea to simplify the intro a little bit. (I didn't simplify everything but just a very little bit, to see what other people think of simplifying it.)

I read the remainder of the article to see how much sense it would make to a lay person and I must say it seems very intelligible to me. Well done! Paul/laudaka (add me to your Y!M/AIM/etc. list if you like!) | Talk 11:02, 26 Feb 2004 (UTC)

Article has been rewritten since this comment was posted. Is the new version okay? --Andrew 20:25, May 11, 2004 (UTC)

Merge

See Talk:Radioactive decay for discussion. This discussion is already long enough. --Smack 22:10, 14 Nov 2004 (UTC)

Old version

This version has major overlaps with the radiation entry and does not really discuss radioactivity. Rewritten. --Andrew 04:18, May 6, 2004 (UTC)

Radioactivity is the ability of an unstable atomic nucleus to transform into a stable product or another unstable product while emitting radiation. This transformation and emission of energy is called radioactive decay. A transformation from one element to another is known as a transmutation. The radiation can be emitted in several forms, including:

a positively charged alpha particle (α), which is the same as a helium nuclei consisting of two neutrons and two protons
a negatively charged beta minus particle (β^-), which is the same as an electron
a positively charged beta plus particle (β⁺), which is the same as a positron, a particle of equal mass but opposite charge of an electron
a gamma ray (γ), which is a photon, a particle with a exceedingly high wave frequency and energy (visible light and radio waves are also photons, as well as all other electromagnetic radiation).

An additional radioactive process is nuclear fission, where some elements can split as a result of absorbing an additional neutron. Such unstable, or fissile, isotopes include uranium-235 and plutonium-239. These are the isotopes used in nuclear reactors and nuclear weapons. When a nucleus splits, there are several decay products including radiation, neutrons, and two new smaller nuclei (usually referred to as fission products).

Radiation is often separated into two categories, ionizing and non-ionizing, to denote the energy and danger of the radiation. Ionization is the process of removing electrons from atoms, leaving two electrically charged particles (ions) behind. Some forms of radiation like visible light, microwaves, or radio waves do not have sufficient energy to remove electrons from atoms and hence, are called non-ionizing radiation. The negatively charged electrons and positively charged nuclei created by ionizing radiation may cause damage in living tissue. The term radioactivity generally refers to the release of ionizing radiation.

If radioactive isotopes are distributed in the environment, they will continue to produce radiation for potentially very long times. This is called radioactive contamination.

History

Radioactivity was first discovered in 1896 by the French scientist Henri Becquerel while working on phosphorescent materials. These materials glow in the dark after exposure to light, and he thought that the glow produced in cathode ray tubes by x-rays might somehow be connected with phosphorescence. So he tried wrapping a photographic plate in black paper and placing various phosphorescent minerals on them. All results were negative until he tried using uranium salts. The result with these compounds was a deep blackening of the plate.

However, it soon became clear that the blackening of the plate had nothing to do with phosphorescence because the plate blackened when the mineral was kept in the dark. Also non-phosphorescent salts of uranium and even metallic uranium blackened the plate. Clearly there was some new form of radiation that could pass through paper that was causing the plate to blacken. [Many books state that Becquerel accidentally discovered radioactivity.]

At first it seemed that the new radiation was similar to then recently discovered x-rays. However further research by Becquerel, Pierre Curie, Marie Curie, Ernest Rutherford and others discovered three of the several different types of radioactivity, namely alpha decay, beta decay, and gamma decay. These researchers also discovered that many other chemical elements (or their isotopes) apart from uranium are radioactive. These radioactive isotopes have many important applications, including tracing biological processes in the human body for diagnosis, preserving foods in jars by killing bacteria, and dating of geological deposits based on assumptions of decay rates and isotope ratios at the time of deposit.

Sources of Radiation

Natural Background Radiation

The earth and all living things on it are constantly bombarded by radiation from space, similar to a steady drizzle of rain. Charged particles from the sun and stars interact with the earth's atmosphere and magnetic field to produce a shower of radiation, typically beta and gamma radiation. The dose from cosmic radiation varies in different parts of the world due to differences in elevation and the effects of the earth's magnetic field.

Radioactive material is found throughout nature. It occurs naturally in the soil, water, and vegetation. The major isotopes of concern for terrestrial radiation are uranium and its decay products, such as thorium, radium, and radon. Low levels of uranium, thorium, and their decay products are found everywhere. Some of these materials are ingested with food and water, while others, such as radon, are inhaled. The dose from terrestrial sources varies in different parts of the world. Locations with higher concentrations of uranium and thorium in their soil have higher dose levels.

In addition to the cosmic and terrestrial sources, all people also have radioactive potassium-40, carbon-14, lead-210, and other isotopes inside their bodies from birth. The variation in dose from one person to another is not as great as the variation in dose from cosmic and terrestrial sources. This means that while excess radiation may be harmful to humans, we are slightly radioactive ourselves.

Synthetic Radiation Sources

Humans can be exposed to synthetic radiation sources in two ways: through direct radiation (as with medical X-rays) or through radioactive contamination, in which radioactive isotopes are released into the environment and humans come in contact with them there. Humans can absorb radiation from such contamination directly, or they can ingest radioactive isotopes which remain in the body, irradiating it from the inside. In this context, alpha particles can be a danger in spite of their low penetration.

The average exposure for a person is about 360 millirems/year, 81 percent of which comes from natural sources of radiation. The remaining 19 percent results from exposure to man made radiation sources. By far, the most significant source of man-made radiation exposure to the general public is from medical procedures, such as diagnostic X-rays, nuclear medicine, and radiation therapy. Some of the major isotopes are I-131 (iodine-131), Tc-99m (technetium-99m), Co-60 (cobalt-60), Ir-192 (iridium-192), Cs-137 (caesium-137), and others.

In addition, the public is exposed to radiation from consumer products, such as tobacco (polonium-210), building materials, combustible fuels (gas, coal, etc.), ophthalmic glass, televisions, luminous watches and dials (tritium), airport X-ray systems, smoke detectors (americium), road construction materials, electron tubes, fluorescent lamp starters, lantern mantles (thorium), etc.

Of lesser magnitude, the public is exposed to radiation from the nuclear fuel cycle, which includes the entire sequence from mining and milling of uranium to the disposal of the used (spent) fuel. The substances involved are uranium and its daughter products.

Occupationally exposed individuals are exposed according to their occupations and to the sources with which they work. The exposure of these individuals to radiation is carefully monitored with the use of tiny instruments called dosimeters or film badges.

Some of the isotopes of concern are cobalt-60, caesium-137, americium-241, and others. Examples of industries where occupational exposure is a concern include:

Fuel cycle
Industrial Radiography
Radiology Departments (Medical)
Radiation Oncology Departments
Nuclear power plants
Nuclear medicine Departments
National (government) and university Research Laboratories
Radioisotope thermoelectric generators

The Effects of Radiation on People

We tend to think of biological effects of radiation in terms of their effect on living cells. For low levels of radiation exposure, the biological effects are so small they may not be detected. The body has defense mechanisms against many types of damage induced by radiation as well as by chemical carcinogens. Consequently, biological effects of radiation on living cells may result in three outcomes:

Injured or damaged cells repair themselves, resulting in no residual damage
Cells die, much like millions of body cells do every day, being replaced through normal biological processes
Cells incorrectly repair themselves resulting in a biophysical change.

The associations between radiation exposure and the development of cancer are mostly based on populations exposed to relatively high levels of ionizing radiation (e.g., Japanese atomic bomb survivors, and recipients of selected diagnostic or therapeutic medical procedures). Cancers associated with high dose exposure include leukemia, breast, bladder, colon, liver, lung, esophagus, ovarian, multiple myeloma, and stomach cancers. Department of Health and Human Services literature also suggests a possible association between ionizing radiation exposure and prostate, nasal cavity/sinuses, pharyngeal and laryngeal, and pancreatic cancer.

The period of time between radiation exposure and the detection of cancer is known as the latent period. Those cancers that may develop as a result of radiation exposure are indistinguishable from those that occur naturally or as a result of exposure to other chemical carcinogens. Furthermore, National Cancer Institute literature indicates that other chemical and physical hazards and lifestyle factors (e.g., smoking, alcohol consumption, and diet) significantly contribute to many of these same diseases.

Although radiation may cause cancer at high doses and high dose rates, public health data do not unequivocally establish the occurrence of cancer following exposure to low doses and dose rates -- below about 10,000 mrem (100 mSv). Studies of occupational workers exposed to chronic low-levels of radiation above normal background have shown no adverse biological effects. Even so, the radiation protection community conservatively assumes that any amount of radiation may pose some risk for causing cancer and hereditary effect, and that the risk is higher for higher radiation exposures. A linear, no-threshold (LNT) dose response relationship is used to describe the relationship between radiation dose and the occurrence of cancer. This dose-response model suggests that any increase in dose, no matter how small, results in an incremental increase in risk. The LNT hypothesis is accepted by the NRC as a conservative model for estimating radiation risk.

High radiation doses tend to kill cells, while low doses tend to damage or alter the genetic code (DNA) of irradiated cells. High doses can kill so many cells that tissues and organs are damaged immediately. This in turn may cause a rapid whole body response often called Acute Radiation Syndrome. The higher the radiation dose, the sooner the effects of radiation will appear, and the higher the probability of death. This syndrome was observed in many atomic bomb survivors in 1945 and emergency workers responding to the 1986 Chernobyl nuclear power plant accident. Approximately 134 plant workers and firefighters battling the fire at the Chernobyl power plant received high radiation doses (70,000 to 1,340,000 mrem or 700 to 13,400 mSv) and suffered from acute radiation sickness. Of these, 28 died from their radiation injuries.

Minimizing Exposure to Radiation

Although exposure to ionizing radiation carries a risk, it is impossible to completely avoid exposure. Radiation has always been present in the environment and in our bodies. We can, however, avoid undue exposure.

There is a range of simple, sensitive instruments capable of detecting minute amounts of radiation from natural and man-made sources. Radiation is very easily detected. In addition, there are four ways in which we can protect ourselves:

Time: For people who are exposed to radiation in addition to natural background radiation, limiting or minimizing the exposure time will reduce the dose from the radiation source.

Distance: In the same way that the heat from a fire is less intense the further away you are, so the intensity of the radiation decreases the further you are form the source of the radiation. The dose decreases dramatically as you increase your distance from the source.

Shielding: Barriers of lead, concrete, or water give good protection from penetrating radiation such as gamma rays and neutrons. This is why certain radioactive materials are stored or handled under water or by remote control in rooms constructed of thick concrete or lined with lead. There are special plastic shields which stop beta particles and air will stop alpha particles. Inserting the proper shield between you and the radiation source will greatly reduce or eliminate the extra radiation dose.

Containment: Radioactive materials are confined in the smallest possible space and kept out of the environment. Radioactive isotopes for medical use, for example, are dispensed in closed handling facilities, while nuclear reactors operate within closed systems with multiple barriers which keep the radioactive materials contained. Rooms have a reduced air pressure so that any leaks occur into the room and not out of it.

Natural and artificial radiations are not different in any kind or effect. Above the background level of radiation exposure, the NRC requires that its licensees limit maximum radiation exposure to individual members of the public to 100 mrem (1 mSv) per year, and limit occupational radiation exposure to adults working with radioactive material to 5,000 mrem (50 mSv) per year.

Measuring Radiation

The amount of radioactivity in a given sample of radioisotope is expressed by the new SI unit, the becquerel (Bq). The old unit was the curie (Ci). One becquerel of a radioisotope is the exact quantity that produces one disintegration per second. The curie is 3.7 x 10¹⁰ Bq disintegrations per second. Thus 1 Bq = 2.7 x 10^-11 Ci and 1 Ci = 3.7 x 10¹⁰ Bq. As the becquerel is as inconveniently small for many uses as the curie was inconveniently large, prefixes such as micro (µ) (10^-6), milli (m) (10^-3), kilo (k) (10³), and so on are routinely used. Following nuclear detonations, the amounts of radioactive material produced are very large and the terms petabecquerel (PBq) (10¹⁵ Bq) and exabecquerel (EBq) (10¹⁸ Bq) may be used. The term megacurie (MCi) (10⁶ Ci) was once used.

See Also

References

The Nuclear Regulatory Commission regulates radiation exposure in the US

Radiogenic

If radiogenic is to redirect here, the intro should make it clear why and what radiogenic means. In particulr, it should make it clear whether radiogenic implies radioactive - is helium radiogenic? Perhaps radiogenic deserves its own entry, though, as it is relevant to methods for dating artifacts. --Andrew 16:20, 7 Jul 2004 (UTC)

Trefoil symbol

That is a picture of a trefoil symbol [1] not a "trifolium" symbol [2].....