Once happens to meet with an unknown object, so there is definitely mercantile, everyday question - how much it weighs.But if it is the unknown - an elementary particle, then what?And nothing, the question remains: what is the mass of the particle.If someone is engaged in counting the costs incurred by mankind to satisfy his curiosity in the study, more precisely measuring the masses of elementary particles, we have learned that, for example, the neutron mass in kilograms with a breathtaking number of zeros after the decimal point, cost humanity more expensivethan the most expensive construction with the same number of zeros before the decimal point.
It all began very casually: J. headed in. Dzh.Tomsonom lab in 1897 were carried out the study of cathode rays.The result has been determined for the universal constant of the universe - the ratio of the electron mass to its charge.Prior to determining the mass of the electron remains very little - to determine its charge.After 12 years, Robert Millikan was able to do it.He experimented with falling droplets in the electric field of oil, and he managed not only to balance the weight of the value of the field, but also to make the necessary measurements and extremely thin.Their result - the numerical value of the mass of the electron:
me = 9,10938215 (15) * 10-31kg.
By this time, and studies of the structure of the atomic nucleus, which has been a pioneer Ernest Rutherford.It was he watching the scattering of charged particles, has proposed a model of the atom with the outer electron shell and the positive nucleus.The particle, which in the planetary model of the atom was offered the role of core simplest atom, was obtained by bombarding nitrogen stream of alpha rays.It was the first nuclear reaction obtained in the laboratory - in its result was obtained from nitrogen and oxygen nuclei of the hydrogen atoms of the future, called protons.However, alpha-rays consist of composite particles: in addition to the two protons they contain two neutrons.The mass of the neutron is almost equal to the mass of the proton and the total mass of the alpha particle turns completely solid in order to destroy the counter-core and break away from it "piece" of what happened.
stream of positive protons deflected by an electric field to compensate for its deviation caused by gravity.In these experiments to determine the mass of a proton is not difficult.But the most interesting was the question of what are the mass ratio of the proton and electron.Riddle was immediately solved: the proton mass exceeds the mass of the electron a little more than 1836 times.
So, originally, the model of the atom assumed by Rutherford as the electron-proton set with the same number of protons and electrons.However, very soon it turned out that the primary nuclear model does not fully describe all observed effects on the interactions of elementary particles.Only in 1932, James Chadwick confirmed the hypothesis of additional particles in the nucleus.They were called neutrons, protons, neutral, becausethey had no charge.This circumstance leads to their great penetrating ability - they do not spend their energy on ionization colliding atoms.The mass of the neutron only slightly greater than the mass of a proton - a total of about 2.6 electron masses more.
chemical properties of substances and compounds that are formed by this element are determined by the number of protons in its nucleus.Over time, it confirmed the participation of the proton in the strong and the other fundamental interactions: electromagnetic, gravitational and weak.At the same time, despite the fact that the charge of the neutron is absent in strong interactions the proton and neutron are considered as elementary particle nucleon in different quantum states.Part of the similarity of the behavior of these particles is due to the fact that the mass of the neutron is very little different from the mass of the proton.The stability of the proton allows the use of pre-accelerated to high speeds, as the bombarding particles for nuclear reactions.
