The word atom, in Greek, means indivisible. This meaning was generally accepted by the scientific community, that atoms were the basic particles of all matter and could not be divided. It was also generally accepted that matter and energy were independent from each other and could not be converted between one another.
With the study of nuclear chemistry, it was found that that the protons, and neutrons that make up the nucleus could be split apart from each other and put back together. In unstable nuclei, this happens naturally, and the nuclei are said to be radioactive. When this happens, a lot of energy is given off. Some particles can also be converted into energy.
Albert Einstein stated that mass and energy are interconvertable. For chemical reactions, they could be treated as independent. But for nuclear reactions, the interconvertability must be considered. He said that the mass of a particle (m) is not constant. It changes with the particle's velocity (v) relative to the observer. A particle's mass is related to its velocity and the velocity of the speed of light (c), by the following equation:
When the particle has no velocity (relative to the observer), v/c becomes zero, and therefore, m = m0. Thus m0 is said to the particle's rest mass. The objects we observe do not move or are not moving fast enough to make any significant change in its mass because c, the speed of light, is a very large number--approximately 2.998 x 108 m/s.
This equation also shows that nothing can move at or faster than the speed of light. As an object approaches the speed of light, v/c approaches the value of 1, and m subsequently becomes much larger. But when an object does attain the speed of light, the value of v/c will become 1, and therefore the denominator of the entire fraction will become zero. Having a denominator of zero is undefined, or not possible. The mass of the object would be infinite. Therefore nothing can attain the speed of light.
The Einstein Equation
E = mc2
shows how one could be calculated from another. The total energy of the universe and all the mass calculated as an equivalent of energy is constant. This is the law of conservation of mass-energy. Since c2 is very large (and c2 even larger--8.988 x 1016), it would take an enormous amount of energy to make even one tiny insignificant amount of matter. For example, let's take the burning of methane:
CH4 + 2O2 ==> CO2 + 2H2O H° = -890 kJ
The 890 kJ of energy released is also accompanied by a loss of mass. Substituting in the values given into the Einstein equation gives us: (In this equation, the definition of a joule is used; 1 J = 1 kg m2 s-2)
The final answer shows that altogether, the products weigh 9.89 nanograms less than the reactants per mole of methane, much too insignificant to be observed by even the most precise balances. Therefore, the energy that was given off, the 890 kJ, came from 9.89 nanograms of matter.
The actual mass of an atomic nucleus is always a little smaller than the sum of the rest masses of all its nucleons (protons and neutrons). This is because some of the mass of the nucleons were changed into energy needed to form the nucleus. This energy is called binding energy. The higher the binding energy, the more stable the nucleus is.
A graph of binding energies vs. mass numbers would show that the binding energy increases as the mass number gets higher until around mass number 60, then it starts to decline from that point on. A region of greatest stability is on the peak of the curve, around a mass number of 55 to 80. Unstable elements with a mass number less than the region tend to undergo fusion (the combination of nuclei) to reach the region. Unstable elements with a mass number greater than the region tend to undergo fission (the splitting of nuclei) to reach the region.
Because a nucleus is made of protons, there has to be a nuclear strong force to keep them together, since they would naturally repel each other. Neutrons in the nucleus also help by keeping the protons farther apart from each other and "diluting" the nucleus.
But when there are too many protons, the proton-proton repulsions build and the nucleus becomes unstable. It carries more energy than other arrangements of nucleons accessible to it. To achieve less energy (and more stability), they undergo radioactive decay, ejecting small nuclear fragments and high-energy radiation.
There are three main types of radiation, alpha, beta and gamma.
Alpha
For example, this is the alpha decay of uranium-238 to thorium-234:
23892U ==> 23490Th + 42He
(When doing nuclear equations, make sure that the mass numbers (the top) and the atomic numbers (the bottom) on each side are equal.)
Beta
Beta radiation is the emission of high energy electrons from the nucleus of an atom. The loss of an electron does nothing to the atomic mass but increases the atomic number by 1. Basically, beta radiation changes a neutron into a proton. The charge of a beta particle is -1. Beta radiation is more penetrating then alpha radiation but lacks the kinetic energy of alpha particles. The wavelength of beta rays is approximately that of X-rays, 10-8 m.
This is the general equation for beta decay:
10n ==> 11p + 0-1e +
neutron ==> proton + beta particle (electron) + antineutrino
An antineutrino accompanies the products also.
Gamma
Gamma radiation (00) is the emission of high energy photons in the range of 10 -10 m, with no matter associated with it. Gamma rays are normally the by product of other alpha or beta emissions. Gamma rays have no effect on either mass or charge, gamma rays only stabilize the nucleus by releasing some of the excess energy. Gamma rays are the most damaging rays being able to penetrate meter thick lead. High energy gamma rays are known as cosmic rays are capable of penetrating kilometers of dense material.
11p ==> 10n + 01e +
When unstable nuclei undergo radioactive decay, their decay rate is not steady. Instead, they have a half-life (t1/2), which is the amount of time required for half of the reactant to disappear. For example, Iodine-131 is unstable and under beta particle emission, it becomes Xenon-131. It has a half life of roughly 8 days. So if we had a 4 gram sample of Iodine-131, in 8 days, there would be 2 grams left. In another 8 days, there would be 1 gram. Alpha radiation is the emission of a helium particle stripped of its electrons. The resulting nucleus is missing 2 protons and 2 neutrons resulting in a charge loss of 2 and mass loss of 4. An alpha particle has a charge of +2. The massive kinetic energy emitted by an alpha particle, upon impact with near by particles, usually causes reactions in those molecules. The largest radiation particle, alpha particles are capable of doing the most damage. However because of its size it cannot penetrate our skin. When the an alpha emitter is in gaseous form it becomes threatening, it no longer has to penetrate skin, it can proceed directly into the lungs causing cancer of the lungs
es.wikipedia.org/wiki/Reactor_nuclear
www.uantof.cl/.../REACTORES%20NUCLEARES.htm
www.foronuclear.org/pdf/.../introduccion_reactoresnucleares.pdf
Other Types
A few synthetic isotopes emit positrons, the antimatter equivalent of an electron (beta particle). A positron is an electron with a positive charge. In positron emission, a proton changes into a neutron, in this general equation: 11p ==> 10n + 01e +
When unstable nuclei undergo radioactive decay, their decay rate is not steady. Instead, they have a half-life (t1/2), which is the amount of time required for half of the reactant to disappear. For example, Iodine-131 is unstable and under beta particle emission, it becomes Xenon-131. It has a half life of roughly 8 days. So if we had a 4 gram sample of Iodine-131, in 8 days, there would be 2 grams left. In another 8 days, there would be 1 gram. Alpha radiation is the emission of a helium particle stripped of its electrons. The resulting nucleus is missing 2 protons and 2 neutrons resulting in a charge loss of 2 and mass loss of 4. An alpha particle has a charge of +2. The massive kinetic energy emitted by an alpha particle, upon impact with near by particles, usually causes reactions in those molecules. The largest radiation particle, alpha particles are capable of doing the most damage. However because of its size it cannot penetrate our skin. When the an alpha emitter is in gaseous form it becomes threatening, it no longer has to penetrate skin, it can proceed directly into the lungs causing cancer of the lungs
Stable nuclides, if plotted on a graph of number of protons vs. number of neutrons, would all fall in an area enclosed by two curved lines known as the band of stability. The band of stability also includes radionuclides because smooth lines cannot be drawn to exclude them. The band of stability also stops at element 83 because there are no known stable isotopes above it. Elements lying outside the band of stability would be too unstable to justify the time and money for an attempt to make it. Another thing that is noticed about the band of stability is that as the number of protons increases, the ratio of neutrons to protons increases. This is because more neutrons are needed to compensate for the increasing proton-proton repulsions. Isotopes occurring above and to the left of the band tend to be beta emitters because they want to lose a neutron and gain a proton. Those lying below and to the right of the band tend to be positron emitters because they want to lose a proton and gain a neutron. Isotopes above element 83 tend to be alpha emitters because they have too many nucleons.
Radionuclides Above Atomic Number 83
Through bombardment, over a thousand isotopes have been made, most of which do not occur naturally. The naturally occurring isotopes above atomic number 83 all have very long half-lives. All the elements from neptunium (atomic number 93) and up, the transuranium elements, are synthetic. Elements up to 109 have been made. To make these heavier elements, bombardment of heavier nuclei are used. For example, there have been attempts to bombard argon-40 and uranium-236 to create element 110. Some interest has been focused on making element 126, one with a magic number.
Current nuclear power plants are powered by nuclear fission, with the science of nuclear fusion emerging.
The key parts to a nuclear power plant (fission) reactor are:
Fuel rods - Fuel rods are usually composed of fissionable isotopes such as 235U, 233U and 239Pu. Any isotope present in critical mass will do. In the U.S. enriched tri-uranium oct-oxide, U3O 8, pellets are placed in a Zirconium alloyed tube where they are lowered into its core.
Control rods - Control rods, normally composed of 10B or Cd, absorb neutrons. Neutrons are absorbed so as to prevent the reaction from going at an unsafe rate (i.e. meltdown).
Moderators - It is job the of the moderator to slow down neutrons without absorbing them. Moderators must slow down neutrons without absorbing or reacting with them. D2O (deuterium oxide--heavy water), H2O, and graphi te are common moderators. If neutrons were permitted to continue uninhibited a chain-reaction would occur causing a meltdown of the facility.
Shielding/Containment - Several products are produced by nuclear reactions, most of which are lethal to humans. The storage and disposal of these materials is an enormous task. Should the facilities where the materials are being held be com promised, that area must be sealed for hundreds to millions of years, until the level of radioactivity has dropped to suitable levels. Inside the reactor several layers of concrete and steel must be laid to prevent radiation from escaping. The steel mus t be replaced periodically be cause exposure to radiation causes it to warp.
Coolant - The job of the coolant is to carry the heat from the reactor to a steam turbine system where it is converted to electricity, as well as keeping the reactor cool enough to prevent a meltdown.
proton ==> neutron + positron + neutrino
Notice that the products of this, the positron and the neutrino, are antimatter equivalents to the electron and antineutrino in the beta emission.
When matter and antimatter come together, their masses change into the energy of two gamma-ray photons called annihilation radiation photons.
0-1e + 01e ==> 200
Neutron emission leads to a different isotope of the same element, for example:
8736Kr ==> 8636Kr + 10n
In electron orbital capture, a very rare type among natural isotopes but common among synthetic ones, a nucleus can capture orbital K shell or L shell electrons. In other words, it is the collapse of an orbital electron into the nucleus, changing a proton into a neutron, and emitting X rays and neutrinos. For example:
5023V + 0-1e ==> 5022Ti + X rays +
Half-Life.
Notice that the products of this, the positron and the neutrino, are antimatter equivalents to the electron and antineutrino in the beta emission.
When matter and antimatter come together, their masses change into the energy of two gamma-ray photons called annihilation radiation photons.
0-1e + 01e ==> 200
Neutron emission leads to a different isotope of the same element, for example:
8736Kr ==> 8636Kr + 10n
In electron orbital capture, a very rare type among natural isotopes but common among synthetic ones, a nucleus can capture orbital K shell or L shell electrons. In other words, it is the collapse of an orbital electron into the nucleus, changing a proton into a neutron, and emitting X rays and neutrinos. For example:
5023V + 0-1e ==> 5022Ti + X rays +
Half-Life.
es.wikipedia.org/wiki/Reactor_nuclear
www.uantof.cl/.../REACTORES%20NUCLEARES.htm
www.foronuclear.org/pdf/.../introduccion_reactoresnucleares.pdf
