It was once believed that the smallest unit of the structure of any substance is a molecule. Then, with the invention of more powerful microscopes, humanity was surprised to discover the concept of an atom - an integral particle of molecules. It would seem, much less? Meanwhile, it later became clear that the atom, in turn, consists of smaller elements.
At the beginning of the 20th century, British physicist Rutherford Ernest discovered the presence of nuclei in the atom - central structures, it was this moment that marked the beginning of a series of endless discoveries concerning the construction of the smallest structural element of matter.
Today, based on the nuclear model of the structure of atoms and thanks to numerous studies, it is known that an atom consists of a nucleus that is surrounded by an electron cloud. The composition of such a "cloud" is electrons, or elementary particles with a negative charge. The nucleus, on the contrary, includes particles with an electrically positive charge, called protons. The British physicist already mentioned above was able to observe and subsequently describe this phenomenon. In 1919, he conducted an experiment in which alpha particles knocked out hydrogen nuclei from the nuclei of other elements. Thus, he managed to find out and prove that protons are nothing but the nucleus of a hydrogen atom without a single electron. In modern physics, protons are denoted by the symbol p or p + (which means a positive charge).
The proton in Greek means "first, main" - an elementary particle belonging to the class of baryons, i.e. relatively heavy elementary particles. It is a stable structure, its life time is more than 2.9 x 10 (29) years.
Strictly speaking, in addition to the proton, the nucleus of the atom also contains neutrons, which, proceeding from the name, are neutrally charged. Both of these elements are called nucleons.
The mass of the proton, due to quite obvious circumstances, could not be measured for a long time. Now it’s known that it is
mp = 1.67262 ∙ 10–27 kg.
This is exactly what the proton rest mass looks like.
Let us turn to the consideration of proton masses specific for different areas of physics.
The mass of a particle in the framework of nuclear physics often takes a different form, its unit of measure is a.u.
A.em. - atomic unit of mass. One amu equals 1/12 of the mass of the carbon atom, the mass number of which is 12. Hence, 1 atomic unit of mass is 1.66057 · 10–27 kg.
The mass of the proton, therefore, is as follows:
mp = 1.007276 a. eat.
There is another way to express the mass of this positively charged particle using other units. To do this, we first need to take as axiom the equivalence of mass and energy E = mc2. Where c is the speed of light, and m is the mass of the body.
The proton mass in this case will be measured in megaelectron-volts or MeV. Such a unit of measurement is used exclusively in nuclear and atomic physics and serves to measure the energy that is needed to transfer a particle between two points in an electrostatic field. With the condition that the potential difference between these points is 1 Volt.
Hence, given that 1 amu = 931.494829533852 MeV, proton mass is approximately
mp = 938 MeV.
Such a conclusion was obtained on the basis of mass spectroscopic measurements, and it is the mass in the form in which it is presented above that is also called the proton rest energy .
Thus, focusing on the needs of the experiment, the mass of the smallest particle can be expressed in three different values, in three different units.
In addition, the mass of the proton can be expressed relative to the mass of the electron, which, as you know, is much "heavier" than a positively charged particle. In this case, the mass will be equal to rough calculation and significant errors will be 1836.152 672 relative to the mass of the electron.