The more simple the organisms are, the more radiation they can tolerate.
A low dose in food irradiation can be applied to fresh fruits and vegetables.
It is enough to prevent or reduce the growth of many organisms, but it is not enough to kill all of them.
High doses in food irradiation and product sterilization are considered.
Fruits and vegetables have longer shelf lives.
They show no loss of taste or vitamins.
If not for the mandatory labeling, low-level irradiation could not be distinguished from high-level irradiation.
Some foods, like lettuce and peaches, have high water content.
Milk has an unpleasant taste.
Changes in foods are produced by high-level irradiation.
It produces a loss of vitamins and some change in taste.
The losses that occur in ordinary freezing and cooking are similar.
Critics argue that the radiolytic products may be harmful.
The safety of irradiated food is not known.
We know that lowlevel food irradiation doesn't produce compounds that can be measured.
It's not surprising that trace amounts of several thousand compounds may be created.
There have been no observable negative effects on consumers.
If a lot of people consume a lot of irradiated food, long-term effects may show up, but no effects have appeared due to the small amount of irradiated food eaten regularly.
The case for safety is supported by the fact that no genetic effects have been observed.
Food irradiation has been endorsed by the World Health Organization and the UN Food and Agricultural Organization.
The benefits of food production and preservation must be weighed against the hazard to consumers.
It needs to be weighed against the real dangers of existing pesticides.
While basking in the warmth of the summer sun, a student reads of the latest breakthrough in achieving sustained thermonuclear power and vaguely recalls hearing about the cold fusion controversy.
Nuclear fusion as an energy source is referred to as thermonuclear power.
While research in the area of thermonuclear power is progressing, high temperatures and containment difficulties remain.
There were claims of fusion power at room temperatures.
Nuclear fusion creates the Sun's energy.
We know that all nuclei have less mass than the protons and neutrons that make them.
The binding energy of the nucleus is equal to the missing mass times.
The binding energy per nucleon is greater for medium-mass nuclei and has a maximum at Fe.
The larger nucleus has more binding energy and less mass than the two that combined.
The details of fusion of low-mass nuclei depend on the nuclides involved.
Mass is destroyed by fusion of light and product nuclei.
Mass is converted to energy and released in fusion reactions if the mass is larger.
The Coulomb repulsion between the nuclei is the main obstruction to fusion.
Repulsion of positive charges is needed to get nuclei close enough to induce fusion since the attractive nuclear force that can do that is short ranged.
The graph is similar to a hill with a well in its center.
A ball that is rolled from the right must have enough energy to get over the hump before it falls into the deeper well.
It is with fusion.
If the nuclei are given enough energy to overcome the electric potential, then they can fall into a deep well.
It is possible to heat fusion fuel to high temperatures to get the nuclei together.
The potential energy between the light nuclei is determined by the distance between them.
If the nuclei have enough energy to get over the Coulomb repulsion hump, they combine, release energy, and drop into a deep attractive well.
In practice, tunneling through the barrier is important.
The higher the energy and the particles get up the barrier, the more likely they are to tunnel.
You might think that the nucleus of the Sun are coming into contact with each other.
The core temperature of the Sun is not enough to get the nuclei in contact with each other.
fusion in the Sun is possible because of quantum mechanical tunneling, which is an important process in most other practical fusion applications.
Increasing the temperature greatly increases the rate of fusion because the probability of tunneling is very sensitive to barrier height and width.
Most fusion in the Sun and other stars takes place at their centers, where temperatures are highest, when the closer reactants get to one another.
thermonuclear power needs high temperature to be a practical source of energy.
They don't have to touch for the reaction to occur as the probability of tunneling increases.
The Sun's most abundant nuclide, hydrogen, is fused into helium to produce energy.
For the third reaction to be possible, the first two must occur twice, so that the cycle consumes six protons.
The two positrons produced will find two electrons and four more rays, for a total of six.
The reactions occur deep in the Sun where the temperatures are the highest.
It takes a long time for the energy to diffuse to the surface.
The Sun is transparent to the neutrinos because they interact so weakly that they escape in less than two seconds.
The Sun acts as a thermostat to regulate the energy output.
If the interior of the Sun becomes hotter than normal, the reaction rate increases, producing energy that expands the interior.
This lowers the reaction rate.
For billions of years, stars like the Sun have been stable.
In introduction to frontiers of physics, what happens is discussed.
Nuclear fusion in the Sun takes place at the boundary of the helium core, where the temperature is highest and enough hydrogen remains.
Energy diffuses slowly to the surface, with the exception of neutrinos, which escape immediately.
Negative feedback effects keep energy production stable.
Hans Bethe, an American physicist who was born in Germany, pioneered theories of the proton-proton cycle.
He made many contributions to physics and society after he was awarded the 1967 Nobel Prize in physics.
Neutrinos produced in these cycles can be used to test theories and study stellar interiors.
Too few solar neutrinos were observed to be consistent with predictions of solar energy production.
The problem of the solar neutrino was solved with a blend of theory and experiment.
There are three different types of neutrinos, each associated with a different type of nuclear decay.
The photomultiplier tubes are part of the large solar neutrino detector.
The flashes of light are detected by the photomultiplier tubes in these experiments.
Even though it's large and has a large amount of neutrinos that strike it, very few are detected each day.
They escape the Sun so readily because of this.
The elements heavier than iron are the result of supernovas.
The powers of energy were released.
There is evidence of heavy elements in the ring of material ejected by Supernova 1987A.
The study of the supernova showed signs of mass.
Despite the abundance of hydrogen, the proton-proton cycle is not a practical source of energy.
There are a number of fusion reactions that are easier to induce.
There is an immense amount of Deuterium in sea water alone.
The fusion reactions produce large energies per reaction, but they do not produce much radioactive waste.
Most of the energy output from the last two reactions is difficult to use.
The three keys to fusion energy generation are to achieve the temperatures necessary to make the reactions likely, to raise the density of the fuel, and to confine it long enough to produce large amounts of energy.
A deficiency in one can be compensated for by the other factors.
The goal of reaching before commercial plants can be a reality has not been achieved.
Hope has been given that commercial plants may become a reality in a few decades, as break-even has nearly been reached.
Two techniques have shown promise.
The charged particles are trapped into a circular path by the tokamak's toroidal coil.
The Tokamak fusion test reactor in the US achieved world-record temperatures in 1995.
This facility was open from 1982 to 1997.
A tokamak-type reactor that will be the stepping stone to commercial power is being built in France.
The goal of ITER is to demonstrate the feasibility of fusion energy.
It will be able to generate 500 MW of power for extended periods of time.
The study will be similar to the fusion power plant.
The completion is scheduled for next year.
The hope is that the machine will break even.
The completion is scheduled for next year.
Multiple lasers aim at tiny fuel pellets filled with a mixture of deuterium and tritium.
The fuel is hot enough to cause the fuel to evaporate and the pellet to be high in density.
With smaller confinement times, higher densities have been reached.
192 laser beams will focus onto a small D-T target in a laser bay.
The mixture has equal numbers of deuterium and tritium.
The energy per reaction is 17.89 MeV.
The number of deuterium and tritium atoms in a kilogram is what we need to find the total energy released.
For a total of about 5 g per mole of reactants, tritium has an atomic mass of about 3 and Deuterium has an atomic mass of about 2.
The atomic mass from Appendix A will be used to get a more precise figure.
The energy output needs to be calculated in joules and then divided by the number of seconds in a year, because the power output is best expressed in watt.