A residential
smoke detector is for most people the most familiar piece of nuclear technology
'Nuclear technology' is technology that involves the
reactions of
atomic nuclei. It has found applications from
smoke detectors to
nuclear reactors, and from
gun sights to
nuclear weapons. There is a great deal of public concern about its possible implications, and every application of nuclear technology is reviewed with care.
History
Discovery
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
Maria Sklodowska-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 several distinct sorts, which they called
alpha rays,
beta rays and
gamma rays.
Some of these kinds of radiation could pass through ordinary matter, and all of them could cause damage in large amounts - all the early researchers received various
radiation burns, much like
sunburn, and thought little of it.
The new phenomenon of radioactivity was seized upon by the manufacturers of
quack medicine (as had the discoveries of
electricity and
magnetism, earlier), and any number of
patent medicines and treatments involving radioactivity were put forward.
Gradually it came to be realized that the radiation produced by radioactive decay was
ionizing radiation, and that quantities too small to burn presented a severe long-term hazard. Many of the scientists working on radioactivity died of
cancer as a result of their exposure.
Radioactive patent medicines mostly disappeared, but other applications of radioactive materials persisted, such as the use of radium salts to produce glowing dials on meters.
As the
atom came to be better understood, the nature of radioactivity became clearer: some atomic nuclei are unstable, and they can decay, releasing energy (in the form of
gamma rays, high-energy
photons) and nuclear fragments (
alpha particles, a pair of
protons and a pair of
neutrons, and
beta particles, high-energy
electrons).
World War 2
During
World War II,
nuclear reactions were sufficiently well understood that all the factions began to see the possibility of constructing a
nuclear weapon. Nuclear reactions release far more energy per reaction than chemical reactions, so if large numbers of reactions could be induced to occur at once, tremendous amounts of energy could be released. The British and the Americans set up the
Manhattan Project under the direction of
Robert Oppenheimer to build such a device.
Radio Activity
Nuclear Fission
Radioactivity is generally a slow and difficult process to control, and is unsuited to building a weapon. However, other nuclear reactions are possible. In particular, a sufficiently unstable nucleus can undergo
nuclear fission, breaking into two smaller nuclei and releasing energy and some
fast neutrons. This neutron could, if captured by another nucleus, cause that nucleus to undergo fission as well. The process could then continue in a nuclear
chain reaction. Such a chain reaction could release a vast amount of energy in a short amount of time.
Nuclear Weapons
The
design of a nuclear weapon is more complicated than it might seem - it is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. The construction of a nuclear weapon is also more difficult than it might seem, as no naturally-occurring substance is sufficiently unstable for this process to occur.
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. Thus a complicated and difficult process of
isotope separation must be performed to obtain uranium-235.
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.
Ultimately,
the Manhattan Project manufactured nuclear weapons based on each of these.
The first atomic bomb was detonated in a test code-named "
Trinity", near
Alamogordo on July 16, 1945. After much debate on the morality of using such a horrifying weapon, two bombs were dropped on the Japanese cities
Hiroshima and
Nagasaki, and the Japanese surrender followed shortly.
The nations that could afford to began nuclear weapons programs, developing ever more destructive bombs in an
arms race to obtain what they called a
nuclear deterrent. Throughout the
Cold War, the opposing powers had huge nuclear arsenals, sufficient to kill hundreds of millions of people. Generations of people grew up under the shadow of nuclear devastation.
However, the tremendous energy release in the detonation of a nuclear weapon also suggested the possibility of a new energy source.
Nuclear Boats
Nuclear submarines were built, able to travel at speed while submerged for months at a time.
Nuclear ships were built, primarily
aircraft carriers, although a few
icebreakers were built. Research projects were started into the possibility of nuclear-powered
aircraft and
nuclear thermal rockets.
Nuclear Power
The first generations of nuclear reactors were built to produce power.
Nuclear safety was a secondary consideration. However, as more nuclear reactors were built, it became clear that they were complex devices in which failures were extremely dangerous.
Nuclear power plants were built to generate household electric power.
Early safety features were primarily concerned with the exposure of operators to intense radiation. However, it was gradually realized that the release of radioactive material into the environment, called
radioactive contamination, was also potentially serious.
Radioactive isotopes of common elements are practically chemically identical to non-radioactive isotopes, so the human body may take up the radioactive materials and deposit them in the
bones,
thyroid,
lungs, or elsewhere. The radioactive materials then decay in place, often leading to cancer.
Types of nuclear reaction
The vast majority of everyday phenomena do not involve nuclear reactions. Most everyday phenomena only involve
gravity and
electromagnetism. Of the
fundamental forces of nature, these are the weakest, but the
strong nuclear force and the
weak nuclear force are essentially short-range forces so they do not play a role outside the atomic nucleus. Atomic nuclei are generally kept apart because they contain positive electrical charges and therefore repel each other, so in ordinary circumstances they cannot meet.
Most natural nuclear reactions fall under the heading of
radioactive decay, where a nucleus is unstable and decays after a random interval. The most common processes by which this can occur are
alpha decay,
beta decay, and
gamma decay. Under suitable circumstances, a large unstable nucleus can break into two smaller nuclei, undergoing
nuclear fission.
If these neutrons are captured by a suitable nucleus, they can trigger fission as well, leading to a
chain reaction. A mass of radioactive material large enough (and in a suitable configuration) is called a
critical mass. When a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. If there are enough immediate decays to carry on the chain reaction, the mass is said to be
prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. However, if the mass is critical only when the delayed neutrons are included, the reaction can be controlled, for example by the introduction or removal of
neutron absorbers. This is what allows
nuclear reactors to be built. Fast neutrons are not easily captured by nuclei; they must be slowed (
slow neutrons), generally by collision with the nuclei of a
neutron moderator, before they can be easily captured.
If nuclei are forced to collide, they can undergo
nuclear fusion. This process may release or absorb energy. When the resulting nucleus is lighter than that of
iron, energy is normally released; when the nucleus is heavier than that of iron, energy is generally absorbed. This process of fusion occurs in stars, and is the way all elements heavier than
helium were produced. Because of the very strong repulsion of nuclei, fusion is difficult to achieve in a controlled fashion.
Fusion bombs obtain their enormous destructive power from fusion, but obtaining controlled
fusion power has so far proved elusive. Controlled fusion can be achieved in
particle accelerators; this is how many
synthetic elements were produced. The
Farnsworth-Hirsch Fusor is a device which can produce controlled fusion (and which can be built as a high-school science project), albeit at a net energy loss. It is sold commercially as a neutron source.
Nuclear Accidents
Three Mile island Incident (1979)
The
Three Mile Island incident, coupled with the release of the disaster film ''
The China Syndrome'' greatly impacted the public's perception of nuclear power. Many
human factors engineering improvements were made to American power plants in the wake of Three Mile Island's partial meltdown.
Chernobyl Accident (1986)
The
Chernobyl accident in
1986 further alarmed the public about nuclear power. While design differences between the
RBMK reactor used at Chernobyl and most western reactors virtually eliminate the possibility of such an accident occurring outside of the former Soviet Union, it is only recently that the general public in the United States has started to embrace nuclear energy.
Examples of Nuclear Technology
Nuclear Power
See
Nuclear Power
Medical Applications
'Imaging' - medical and dental x-ray imagers use of Cobalt-60 or other x-ray sources.
Industrial Applications
'Oil and Gas Exploration'- Nuclear
well logging is used to help predict the commercial viability of new or existing wells. The technology involves the use of a neutron or gamma-ray source and a radiation detector which are lowered into boreholes to determine the properties of the surrounding rock such as porosity and lithography.
[1]
'Road Construction' - Nuclear moisture/density gauges are used to determine the density of soils, asphalt, and concrete. Typically a Cesium-137 source is used.
Food Processing and Agriculture
In an effort to find new markets for
isotopes, the
Canadian nuclear industry is promoting the use of intense
radiation from
cobalt-60 to kill
insects and
microbes in
spices,
fruit,
poultry,
grain and other foodstuffs. The purpose is to prolong
shelf life. A similar technology is used to
sterilize medical equipment.
A
Parliamentary committee recommended against the use of
food irradiation without further study.
Irradiation creates new
chemical substances (
radiolytic products) in the food, some of which are
carcinogenic. Children fed irradiated wheat have shown
chromosome damage. As well, irradiating food reduces the vitamin content.
The industry proposes that irradiated food be labeled inconspicuously to minimize consumer anxiety.
[1]
References
1. Source: http://www.ccnr.org/nuclear_primer.html#NF
See also
★
Nuclear Energy Institute – Beneficial Uses of Radation
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