What is the mass converted to in nuclear reactions?

Answer 1

Nuclear fusion is a subject in which most nuclear engineers have little knowledge and no experience, however the following is extracted from Wikipedia entries. A contribution from someone with experience in this field would be welcome.

The most successful fusion experiment so far is believed to be in the Joint European Torus (JET) which was built in the UK. In 1997 this achieved a peak fusion power of 16.1 MW, with more than 10 MW sustained for 0.5 sec. The heat generated by the fusion was 65 percent of the heat input. This experiment used the deuterium/tritium fuel reaction, which is the most promising on theoretical predictions.

The next step is to build a larger experiment which could be a prototype for a power producing plant if successful. This is called ITER and will be built in France, but is an international effort with most nuclear power countries involved. Building is due to start in 2008. In this design, up to 500 MW is hoped for with a burn time up to 400secs, consuming about 0.5 grams of the D/T mixture, so this gives some idea of the mass to energy conversion. Most of the energy from fusion will appear in the fast neutrons produced, which will be absorbed in shielding material surrounding the fusion chamber. There is considerable doubt about what materials could stand this intense neutron bombardment, and in general materials seem to be the main unknown. This ITER experiment will produce 5 to 10 times the energy put in to heat the plasma, if predictions are right. Results will probably not be produced for 10 years or more from now.

Answer 2

Mass is converted1 into energy in nuclear fusion for the same reason it is converted1 to energy in nuclear fission - the release of binding energy. It just happens that the delta mass (before and after the reaction) in fusion is much greater than in fission.

One way to look at it is to think about the atoms. You either split them (fission) or you fuse them (fusion). When you are done, the mass of the result is less than the original masses of the components. That mass is converted1 to energy using Einstein's equation e = mc2. Since c2 is a very large number, 9 x 1016, the energy to mass ratio is tremendous.

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1 From a purist standpoint, mass is not "converted" to energy. Mass is energy, and energy is mass. Mass can neither be created nor destroyed, and the same goes for energy - they can only be moved from one frame of reference to another. It is more correct to say that energy is released by the fission or fusion of mass. One responder to this type of question is quoted as saying "the mass is carried away by the energy". (I believe the origin of that quote is either Mrkbh or WikiPedia, but I'm not sure.)

Answer 3

Into another type of mass. And the energy is transformed into a different type of energy.

I think it might be more correctly stated that mass is converted to energy through the process of nuclear fusion. The process of fusing a pair of protons releases a huge quantity of energy as per Einstein's great equation E=mc^2. The resultant nuclei formed through the nuclear fusion process will have a total mass slightly less than the sum of the masses of the original two protons; that loss in total mass of the fused protons is the mass that was converted to energy.

Answer 4

There is a misunderstanding here. It is a fine, but very important point. Mass can neither be created nor destroyed, and energy can neither be created nor destroyed.

There is a relationship between mass and energy, in the relativistic framework set down by Einstein in his famous mass-energy equivalence equation e = mc2. Do not misunderstand, however - this does not mean that mass can be converted to energy and vice versa - it means that mass has energy, and energy has mass, all depending on relativistic velocity.

In nuclear fission, the nuclear force (residual binding energy) that holds protons and neutrons together in an atom is greater than the nuclear force required to hold the protons and neutrons together in the split atoms that result from the fission process. The differential nuclear force, or mass deficit, is released during fission. It is more correct to say that the mass is carried away with the energy, because the mass is the energy and the energy is the mass, as stated above.

Answer 5

Alex146 has the nuclear fission description exactly backwards. he says "In nuclear fission, the nuclear force (residual binding energy) that holds protons and neutrons together in an atom is greater than the nuclear force required to hold the protons and neutrons together in the split atoms that result from the fission process. "

The total binding energy of the original atom (e.g. U-235) is LESS than the total binding energy of the two products. This is evidenced by the fact that the mass of the U-235 plus a neutron (which triggers the instability) is MORE than the combined mass of the two products and whatever (2-5) neutrons that are thrown out of the fission reaction. Binding energy can be thought of as missing mass energy, "missing" compared to the total mass of the individual protons and neutrons.

The binding energy of U-235 would be 92 proton masses + 143 neutron masses - U-235 mass = 1784 MeV. Typical fission products would be Sr-90 and Xe-145 (with no neutrons out) and a total of the two binding energies of 1963 MeV. thus a release of 179 MeV in the form of kinetic and electromagnetic energy.

Answer 6

Too early to say, nobody has designed a practical fusion power plant yet

Answer 7

Energy. Initially this will go into kinetic energy of the fission fragments, which is then quickly converted to thermal energy

Answer 8

I found the website K1 Project very helpful. They had several articles underneath their Learn/Energy tab which should answer any questions about nuclear fusion.

Answer 9

That would depend on how much fuel you use.

Answer 10

It is expected to be 1000% efficient (Produce ten times as much energy as it uses).

Source, Howstuffworks website