Rest mass of proton

It was stated above that the Schrodinger equation cannot be solved exactly for any molecular systems. However, it is possible to solve the equation exactly for the simplest molecular species, Hj (and isotopically equivalent species such as ITD" ), when the motion of the electrons is decoupled from the motion of the nuclei in accordance with the Bom-Oppenheimer approximation. The masses of the nuclei are much greater than the masses of the electrons (the resting mass of the lightest nucleus, the proton, is 1836 times heavier than the resting mass of the electron). This means that the electrons can adjust almost instantaneously to any changes in the positions of the nuclei. The electronic wavefunction thus depends only on the positions of the nuclei and not on their momenta. Under the Bom-Oppenheimer approximation the total wavefunction for the molecule can be written in the following form ... 

Proton—Elementary nuclear particle with a positive electric charge equal numerically to the charge of the electron and a rest mass of 1.007 mass units. 

Atomic mass The at-rest mass of an atom. It is usually measured in atomic mass units or amu, which is defined as exactly one-twelfth the mass of an atom of carbon-12, the isotope of carbon with six protons and six neutrons in its nucleus. One amu is equal to approximately 1.66 x 10 24 grams. 

All atomic nuclei consist of Z protons and N neutrons. The total rest mass of the energy of the individual particles is always greater than the rest mass energy of the nucleus. The deficit represents the binding energy of the nucleus... 

The simplest p-p chain begins with the p-p reaction already discussed. The rest mass of the proton is 1.00728 u, where u is the atomic mass unit, 1 /12th the mass of a 12C atom. The fusion of two protons, including a positron decay, yields a deuterium nucleus with rest mass 2.01355 u. The energy excess is thus... 

Making allowance for the energy carried away by the 2 neutrinos (2 x 0.25 MeV) this leaves a total of 26.22 MeV for radiation, i.e. 4.20 pJ per atom of helium or 2.53 x 10 kJ mol . This vast release of energy arises mainly from the difference between the rest mass of the helium-4 nucleus and the 4 protons from which it was formed (0.028 atomic mass units). There are several other peripheral reactions between the protons, deuterons and He nuclei, but these need not detain us. It should be noted, however, that only 0.7% of the mass is lost during this transformation, so that the star remains approximately constant in mass. For example, in the sun during each second, some 600 x 10 tonnes (600 x 10 kg) of hydrogen are processed into 595.5 x 10 tonnes of helium, the remaining... 

Neutrons and electrons are two of the elemental particles of matter. A neutron in its free state is unstable (P-decay to an electron and a proton within a haif-iife of about 12 minutes it has a rest mass of 1.675 10-27 kg and no eieotric oharge). The eiectron has oniy 1/1839 of the neutron mass (9.109x10-31 kg), and its charge is negative (- 1). 

Also of note is the fact that the mass of an isotope is not exactly equal to the Slim of the masses of the protons and neutrons within the nucleus of the respective atom (electrons are not considered as their masses are a small fraction of the proton/neutron s masses). Rest masses of free protons, neutrons, and electrons are listed along with their mass in unified atomic mass units and their charge in units of coulombs in Table 2.1. 

As an example, the mass of the " He isotope is 4.0026 u, whereas the sum of the rest masses of free proton and neutrons (see Table 2.1) is 4.0320 u. This loss of mass arises from the fact that energy is required to overcome the electromagnetic repulsion experienced as two or more protons brought in close vicinity to each odier. This energy is attained at the expense of mass consistent with the equation E = mc where c is the speed of light (this is the basis of how fusion reactors derive energy). 

An atom contains electrons and protons. Since mass is associated with all matter, it is natural to assume that atoms, which form matter, have mass. And since any sample of matter occupies a certain volume, we can also assume that each atom has volume. Almost all the mass of the atom is concentrated in a region that is much smaller than the total volume of the atom. This region is called the nucleus of the atom. The rest of the volume of the atom is occupied by electrons. 

Now our nuclear model suffices. We can build up the atoms for all elements. Each atom has a nucleus consisting of protons and neutrons. The protons are responsible for all of the nuclear charge and part of the mass. The neutrons are responsible for the rest of the mass of the nucleus. The neutron plays a role in binding the nucleus together, apparently adding attractive forces which predominate over the electrical repulsions among the protons. ... 

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