Re: When matter and antimatter meet....

The short answer to your question, John, is that the only thing left when matter and antimatter meet is radiation, and in general it is hard gamma radiation that could potentially be hazardous.

When matter meets antimatter (for example, when an electron encounters a positron) the two particles annihilate into electromagnetic radiation. Conservation of energy requires that the final radiation must have exactly as much energy as the mass-energy of the original two particles. You also have to include the kinetic energy of the particles, and any binding energy if one or the other is part of an atom, but these values are usually pretty small relative to the mass energy. Recall Einstein's famous equation E=mc- squared. The value of c, the speed of light, is a very large number, so when squared and multiplied by the mass of even an unimaginably small particle like an electron, you get pretty energetic radiation.

By far the most common annihilation is to form one photon of radiation for each original particle. In the case of electrons and positrons, they each have 511,000 electron-volts (eV) of energy. So annihilation forms two 511 keV gamma rays. An eV is the amount of energy gained by an electron if accelerated through a one-volt potential. To give an electron kinetic energy equal to its mass energy, you would have to put it through 511 kilovolts. Sounds like alot, but to keep this in perspective, when you eat a typical donut, you gain over a trillion-trillion (10^24) electron-volts of chemical energy. We usually use the more convenient unit of calories.

In terms of radiation, photons of visible light are only a few eV, x- rays are typically hundreds or thousands of eV, and microwaves are less than a thousandth of an eV. The annihilation of a proton and an anti-proton would produce billion-eV gamma-ray photons.

Keep in mind that even though the individual photons are energetic, you also have to consider the total number of photons when looking at harm to living things. A single gamma ray will only interact a couple of times in your body, producing minor damage that is quickly repaired. As indicated by our donut calculation, the total energy deposited is pretty minimal; however, if you wanted to use matter-antimatter as an energy-storage system, then all the energy required to run the Enterprise would initially be released as high-energy gamma rays. Have fun converting that safely to heat or electricity. (The energy-source option assumes you can find a ready natural source of antimatter - making it yourself is a very, very inefficient process.) Stay curious, Jay