Another form of nuclear energy is called fusion. Fusion means joining smaller nuclei (the plural of nucleus) to make a larger nucleus. The sun uses nuclear fusion of hydrogen atoms into helium atoms. This gives off heat and light and other radiation.
In the picture to the right, two types of hydrogen atoms, deuterium and tritium, combine to make a helium atom and an extra particle called a neutron.
Also given off in this fusion reaction is energy! Thanks to the University of California, Berkeley for the picture.
Scientists have been working on controlling nuclear fusion for a long time, trying to make a fusion reactor to produce electricity. But they have been having trouble learning how to control the reaction in a contained space.
What's better about nuclear fusion is that it creates less radioactive material than fission, and its supply of fuel can last longer than the sun.
Friday, June 11, 2010
Nuclear Fusion
Nuclear Fusion
Nuclear Fission
Nuclear Fission
"fuel." Uranium is an element that is dug out of the ground many places around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the power plant's reactor.
The word fission means to split apart. Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction.
In a chain reaction, particles released by the splitting of the atom go off and strike other uranium atoms splitting those. Those particles given off split still other atoms in a chain reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it doesn't go too fast.
If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held together, with great force. These conditions are not present in a nuclear reactor.
The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. The very strong concrete dome in the picture is designed to keep this material inside if an accident happens.
This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So, instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy of atoms into heat energy.
An atom's nucleus can be split apart. When this is done, a tremendous amount of energy is released. The energy is both heat and light energy. Einstein said that a very small amount of matter contains a very LARGE amount of energy. This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it can make a tremendous explosion in an atomic bomb.
"fuel." Uranium is an element that is dug out of the ground many places around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the power plant's reactor.The word fission means to split apart. Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction.
In a chain reaction, particles released by the splitting of the atom go off and strike other uranium atoms splitting those. Those particles given off split still other atoms in a chain reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it doesn't go too fast.
If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held together, with great force. These conditions are not present in a nuclear reactor.
The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. The very strong concrete dome in the picture is designed to keep this material inside if an accident happens.
This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So, instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy of atoms into heat energy.
This water from around the nuclear core is sent to another section of the power plant. Here, in the heat exchanger, it heats another set of pipes filled with water to make steam. The steam in this second set of pipes turns a turbine to generate electricity. Below is a cross section of the inside of a typical nuclear power plant.
Power plant drawing courtesy Nuclear Institute
Thursday, June 10, 2010
Heat Pipes
Heat Pipes
As the density of transistors in a microprocessor increases, the amount of heat disipated increases. A Pentium 4 processor (180 nm running at 2GHz) disipates, 55 Watts of power as heat. Its area is just 131 mm2. This gives a 55 W/(131/(102)) = 42 W cm-2. In comparison a steam iron is 5 Wcm-2.
One solution is the heat pipe. As its name suggests, it transfers heat from high temperature regions to lower temperature regions where there is more space for heat sinks or cooling fans.
Inside a heatpipe
Although it just looks like a sealed metal pipe, there is a wick or porous material and a liquid with a high latent heat of vaporization. When the pipe is heated the liquid uses the heat to evaporate and changes into a gas, the gas moves to a colder region of the heat pipe where is condenses and uses the latent heat to change back into a liquid. Heat pipes are a reliable and cost effective solution for laptop computers where fans would reduce battery life.
As the density of transistors in a microprocessor increases, the amount of heat disipated increases. A Pentium 4 processor (180 nm running at 2GHz) disipates, 55 Watts of power as heat. Its area is just 131 mm2. This gives a 55 W/(131/(102)) = 42 W cm-2. In comparison a steam iron is 5 Wcm-2.
One solution is the heat pipe. As its name suggests, it transfers heat from high temperature regions to lower temperature regions where there is more space for heat sinks or cooling fans.
Inside a heatpipe
Although it just looks like a sealed metal pipe, there is a wick or porous material and a liquid with a high latent heat of vaporization. When the pipe is heated the liquid uses the heat to evaporate and changes into a gas, the gas moves to a colder region of the heat pipe where is condenses and uses the latent heat to change back into a liquid. Heat pipes are a reliable and cost effective solution for laptop computers where fans would reduce battery life.
The Phases of Matter
The Phases of Matter
Matter can exist in several distinct forms which we call phases. We are all familiar with solids, liquids and gases. Whether a substance is a solid, liquid or gas depends on the potential energy in the atomic forces holding the particles together and the thermal energy of the particle motions. The pressure on the subtance also has an effect on the phase.
Solids
Crystaline Solids
Crystaline solids are characterised by a long-range order. The atoms are closely packed on lattice points held in in place by atomic bonds. The internal energy of the atoms is not sufficient to allow the atoms to break away from their lattice positions. Examples of crystaline solids include semiconductors, quartz, salt, etc.
Amorphous Solids
Amorphous Solids are still closely packed together but lack the translational symmetry of crystaline solids. However, even amorphous solids have relatively good spatial ordering, especially over small distances, (10-100 molecules)
Liquids
As the material is heated, the internal energy is increased and the atoms are no longer tied to their lattice positions but can move relative to each other although the atoms are still closely packed together.
Gases
A gas is matter in which the molecules are widely separated, move around freely, and move at high speeds. Examples of solids include the gases we breathe (nitrogen, oxygen, and others), the helium in balloons, and steam (water vapor).
The solid, liquid and gas phases of matter.
Plasmas
Eventually, given enough heat, the electrons and nucleus become separated and into positively, charged ions and negatively charged electrons. This soup of ions and electrons is known as a plasma
Phase Diagrams
The phases of the material can be recorded for many different pressures and temperatures. Plotting the phases, whether the material is solid, liquid or gas for many different pressures and temperatures we can build up a phase diagram for the substance.
Phase Diagram for water
Matter can exist in several distinct forms which we call phases. We are all familiar with solids, liquids and gases. Whether a substance is a solid, liquid or gas depends on the potential energy in the atomic forces holding the particles together and the thermal energy of the particle motions. The pressure on the subtance also has an effect on the phase.
Solids
Crystaline Solids
Crystaline solids are characterised by a long-range order. The atoms are closely packed on lattice points held in in place by atomic bonds. The internal energy of the atoms is not sufficient to allow the atoms to break away from their lattice positions. Examples of crystaline solids include semiconductors, quartz, salt, etc.
Amorphous Solids
Amorphous Solids are still closely packed together but lack the translational symmetry of crystaline solids. However, even amorphous solids have relatively good spatial ordering, especially over small distances, (10-100 molecules)
Liquids
As the material is heated, the internal energy is increased and the atoms are no longer tied to their lattice positions but can move relative to each other although the atoms are still closely packed together.
Gases
A gas is matter in which the molecules are widely separated, move around freely, and move at high speeds. Examples of solids include the gases we breathe (nitrogen, oxygen, and others), the helium in balloons, and steam (water vapor).
The solid, liquid and gas phases of matter.
PlasmasEventually, given enough heat, the electrons and nucleus become separated and into positively, charged ions and negatively charged electrons. This soup of ions and electrons is known as a plasma
Phase Diagrams
The phases of the material can be recorded for many different pressures and temperatures. Plotting the phases, whether the material is solid, liquid or gas for many different pressures and temperatures we can build up a phase diagram for the substance.
Phase Diagram for water
Electric Current
Electric Current
Electric current is the flow of charge. The SI unit of current is the Amp. [A].
In mathematical terms we can describe the current as the rate of change of charge with time.
I = dQ/dt.
In order for the charge to flow there has to be a potential difference. V.
Microscopic Description
To produce a current the charge needs to flow in a conductor. This charge is carried by electrons. Consider a section of wire of length l and cross-section A, in which there is a potential difference. Electrons flow from the higher potential to the lower potential.
The total charge per unit volume = n
Therefore the total charge is dQ = nqAl, since Al is the volume of the wire and q is the charge on the electron.
If the electrons are moving at a speed vd. Then dt is l/vd seconds for the electrons to pass the point X.
The current I = dQ/dt = nqAvd
Free Electron Density
To calculate the number of electrons per unit volume in a metal we need to know some basic data such as the molar mass of the metal, density, the number of free electrons or valancy.
n = ρNA/M
If we know the current I and the number of electrons n we can calculate the drift-velocity. vd.
The drift-velocity is actually only around a millimeter per second.
For example, a current of 1 A at 6 V, how many electrons pass per second in a copper wire,
Conventional Current
One of the confussing aspects of current is the direction in which the current flows. It is an accident of history that the current was a flow of positive charge carriers. However, in metal conductors, the positive ions are not able to move and the flow of charge is a result of negative electrons. As a result the true direction of the current flow is in the opposite direction to the conventional current. It does not matter which is used as long as you are consistent.
To make it absolutely clear:
The conventional current flows from positive to negative.
The electron flows from negative to positive.
Electric current is the flow of charge. The SI unit of current is the Amp. [A].
In mathematical terms we can describe the current as the rate of change of charge with time.
I = dQ/dt.
In order for the charge to flow there has to be a potential difference. V.
Microscopic Description
To produce a current the charge needs to flow in a conductor. This charge is carried by electrons. Consider a section of wire of length l and cross-section A, in which there is a potential difference. Electrons flow from the higher potential to the lower potential.
The total charge per unit volume = n
Therefore the total charge is dQ = nqAl, since Al is the volume of the wire and q is the charge on the electron.
If the electrons are moving at a speed vd. Then dt is l/vd seconds for the electrons to pass the point X.
The current I = dQ/dt = nqAvd
Free Electron Density
To calculate the number of electrons per unit volume in a metal we need to know some basic data such as the molar mass of the metal, density, the number of free electrons or valancy.
n = ρNA/M
If we know the current I and the number of electrons n we can calculate the drift-velocity. vd.
The drift-velocity is actually only around a millimeter per second.
For example, a current of 1 A at 6 V, how many electrons pass per second in a copper wire,
Conventional Current
One of the confussing aspects of current is the direction in which the current flows. It is an accident of history that the current was a flow of positive charge carriers. However, in metal conductors, the positive ions are not able to move and the flow of charge is a result of negative electrons. As a result the true direction of the current flow is in the opposite direction to the conventional current. It does not matter which is used as long as you are consistent.
To make it absolutely clear:
The conventional current flows from positive to negative.The electron flows from negative to positive.
Beyond the Solar System
Beyond the Solar System
Stars
Stars are large masses of gas that have been formed by the action of their own gravitation. The pressure of the gas under gravity has caused the gases to become so hot that nuclear fusion can initiate. The smallest star is around 97 Jupiter masses while the largest are about 150 solar masses.
Galaxies
Galaxies are large systems of stars and interstellar matter, typically containing several million to some trillion stars. The mass a galaxy is between several million and several trillion times that of our Sun. The distance across a galaxy can extension of a few thousands to several 100,000s light years. Typically, individual galaxies are separated by millions of light years distance. They come in a variety of shapes: Spiral, lenticular, elliptical and irregular. Besides simple stars, they typically contain various types of star clusters and nebulae.
Hubble classification of galaxies.
Our own galaxy is a giant spiral galaxy, the Milky Way Galaxy, which is 100,000 light years in diameter and a mass of roughly a trillion solar masses. The nearest dwarf galaxies, satellites of the Milky Way, are only a few 100,000 light years distant, while the nearest giant neighbor, the Andromeda Galaxy, also a spiral, is about 2-3 million light years distant.
On a larger scale of the universe there are clusters of galaxies, superclusters
Exotic matter, black holes, quasars, pulsars
Radiation
Stars
Stars are large masses of gas that have been formed by the action of their own gravitation. The pressure of the gas under gravity has caused the gases to become so hot that nuclear fusion can initiate. The smallest star is around 97 Jupiter masses while the largest are about 150 solar masses.Galaxies
Galaxies are large systems of stars and interstellar matter, typically containing several million to some trillion stars. The mass a galaxy is between several million and several trillion times that of our Sun. The distance across a galaxy can extension of a few thousands to several 100,000s light years. Typically, individual galaxies are separated by millions of light years distance. They come in a variety of shapes: Spiral, lenticular, elliptical and irregular. Besides simple stars, they typically contain various types of star clusters and nebulae.
Hubble classification of galaxies.
Our own galaxy is a giant spiral galaxy, the Milky Way Galaxy, which is 100,000 light years in diameter and a mass of roughly a trillion solar masses. The nearest dwarf galaxies, satellites of the Milky Way, are only a few 100,000 light years distant, while the nearest giant neighbor, the Andromeda Galaxy, also a spiral, is about 2-3 million light years distant.On a larger scale of the universe there are clusters of galaxies, superclusters
Exotic matter, black holes, quasars, pulsars
Radiation
Bubble Fusion
Bubble Fusion
Sonoluminesence is the production of light from sound. It was first obversed in 1934, yet comparatively little is known about the process. Ultrasound in water can lead to the expansion and contraction of small bubbles dissolved in the water. In the reifaction, the bubble expands while during the compression, the bubbles collapse rapidly (1.4 km s-1 at the point of light emission) leading to a compression of the gas inside. The compression halts when the van der Vaals forces between molecules will not allow them to get any closer. The mechanism for the light emission is proposed by the shock-wave model.
The shock-wave model of sonoluminescence has the collapsing bubble generate an imploding shock-wave which focuses at a point. As the shock-wave propagates, it heats and intensifies the gas it passes through. At the focus, the shock-wave bounces back and makes the gas even hotter. Light is emitted because the shock-wave heats the gas enough to become ionised. The electrons emit light when they collide with the ions which results in the observed continuous emission spectra.
Experiments measuring the emission wavelength, show it to correspond to an energy of around 6 eV, which in turn, corresponds to a temperature inside a collapsing bubble of 70,000 K. There may be photons of even higher energy which would mean higher temperatures, but these wavelengths are absorbed by the water so it is not known what the maximum temperature inside the collapsing bubble is. It is at this point we turn our attention to fusion.
While 70,000 K is far below the 100 million K required for fusion, the temperature of the gas in the centre depends on the minimum size of the of the collapsing bubble. This is another unknown. The so-called shock radius, the radius of the bubble at the point of sonoluminescence, is around 0.1 μm but its minimum size could be smaller for an emission energy of 6 eV. If the radius of the bubble reaches 10 nm (just 10 times smaller) and the gas inside where deuterium, fusion could be ignited. Experiments producing sonoluminescence in deuterated acetone have claimed to produce nuclear fusion with the tell-tale emission of neutrons. Once again, the reproducibility of these results is at issue since it is very difficult to tell whether the neutrons were produced by nuclear processes or part of the background neutron count.
Sonoluminesence is the production of light from sound. It was first obversed in 1934, yet comparatively little is known about the process. Ultrasound in water can lead to the expansion and contraction of small bubbles dissolved in the water. In the reifaction, the bubble expands while during the compression, the bubbles collapse rapidly (1.4 km s-1 at the point of light emission) leading to a compression of the gas inside. The compression halts when the van der Vaals forces between molecules will not allow them to get any closer. The mechanism for the light emission is proposed by the shock-wave model.
The shock-wave model of sonoluminescence has the collapsing bubble generate an imploding shock-wave which focuses at a point. As the shock-wave propagates, it heats and intensifies the gas it passes through. At the focus, the shock-wave bounces back and makes the gas even hotter. Light is emitted because the shock-wave heats the gas enough to become ionised. The electrons emit light when they collide with the ions which results in the observed continuous emission spectra.
Experiments measuring the emission wavelength, show it to correspond to an energy of around 6 eV, which in turn, corresponds to a temperature inside a collapsing bubble of 70,000 K. There may be photons of even higher energy which would mean higher temperatures, but these wavelengths are absorbed by the water so it is not known what the maximum temperature inside the collapsing bubble is. It is at this point we turn our attention to fusion.
While 70,000 K is far below the 100 million K required for fusion, the temperature of the gas in the centre depends on the minimum size of the of the collapsing bubble. This is another unknown. The so-called shock radius, the radius of the bubble at the point of sonoluminescence, is around 0.1 μm but its minimum size could be smaller for an emission energy of 6 eV. If the radius of the bubble reaches 10 nm (just 10 times smaller) and the gas inside where deuterium, fusion could be ignited. Experiments producing sonoluminescence in deuterated acetone have claimed to produce nuclear fusion with the tell-tale emission of neutrons. Once again, the reproducibility of these results is at issue since it is very difficult to tell whether the neutrons were produced by nuclear processes or part of the background neutron count.
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