User:Fatima tarhini

An atom consists of a positive charged atomic nucleus where you can find protons and neutrons and it consists of a negative charged atomic shell with electrons. In every atom the number of the electrons is equal to the number of the protons so it is neutral. The number of the protons decides which chemical element the atom is. The first element in the "Periodic table of the elements" is hydrogen. The elements in the "Periodic table of the elements" are sorted by the number of the protons. The atomic nucleus of a hydrogen atom consists of only one proton. But there are a few isotops of every element. Isotops are atoms with the same number of protons, but another number of neutrons. The different isotops of one element do not differ in their chemical properties. There are for example three isotops of hydrogen. The first isotop is the one I wrote about. The second isotop of hydrogen is deutrium with one proton and one neutron in his atomic nucleus and the third isotop is tritium which has got one proton and two neutrons in his atomic nucleus. In the atomic nucleus of a tritiumatom there is no balance between the protons and the neutrons so it is instable and decays. The particle which is emited from this decay is radioaktiv and it is charged. You can make ions of atoms. We can say that an ion is an atom which has got less or more electrons than protons. An ion is not neutral an so it is radioactif

Radioactivity means that atoms decays. The reason for this decays is that they are instable. A atomic nucleus is instable when he is to heavy or when a balance is missing between the protons and the neutrons. Every atom which has got a higher number of nucleons (protons and neutrons togehter) than 210 is instable. There are three types of decays: alpha decay, beta decay and gamma decay. Because it is impossible today to say which atomic nucleus will be the next who decays there statistics. We can say how many atomic nucleus will decay in a certain time. This is the princip for half lifes. After one half life a half of the atomic nucleus of a certain material decayed. Plutonium-239 for example has got a half life 24,000 years, radium-228 has got a half life of 6.7 years, thorium-232 has got a half life of 14,000,000,000 years and polonium-212 has got a half life 0.0000003 seconds. There are many physical properties, but I will talk about the acivity now. The activity is the number of decays devided by a certain time. the unit of the activity is becquerel. 1 becquerel is one decay per second. So 20 becquerels are 20 decays per second. To prove these decays there is a geiger counter. It consists of a closed tube which is often filled with argon. At the end of the tube there is a wire, which is not allowed to touch the other end of the tube or the walls. The wire is charged positive and the walls are charged negative. A radioactive particle which flows into the tube ionizes one or a few gas atoms. The out-pushed electrons go to the wire. The consequence is a voltage surge. This voltage surge is shown on an output device as a decay. On the photo there shown a geiger counter. There are many nuclear reactions, but I will only discribe the nuclear fission and the nuclear fusion. For a nuclear fission in a nuclear power plant or for an explosion of a nuclear bomb you need plutonium-239 or uranium-235 as a split material. To make a nuclear fission it is necessary to bombard the split material with thermal neutrons. After the fission there there are two new atoms and and two or three free neutrons. This free neutrons make a fission of other atoms and so it is a nuclear chain reaction.

In a nuclear bomb there is a globe made of plutonium-239 or uranium-235. In this globe there is a neutron source which only effective when the TNT (trinitrotoluene) exploses. Because of the compression of the explosion the critical mass of the split material is overstepped. There are nuclear bomb which are build otherwise, but the princip is always the same. This both materials are very expensive, because on earth we find very little plutonium so it means that we must produce plutonium. To produce plutonium it is necessary to bombard the natural and very cheap uranium-238 with neutrons to make uranium-239. Uranium-239 decays to neptunium-239 and neptunium-239 decays after a certain time to plutonium-239. You can find uranium-235 in nature, but only in uranium-238. To split this uranium-235 from uranium-238 is very expensive, because their chemical properties are the same so it is not possible to split them in a chemical way. A nuclear bomb like this can have an explosion force of 20 kilotons (20000 tons). This means that an explosion of such a bomb is as effective as the explosion of 20 kilotons of TNT.