|||
| charge in coulombs | relative to a proton | mass in kilograms | relative to a proton | |
|---|---|---|---|---|
| proton | 1.6×10−19 | +1 | 1.67×10−27 | 1 |
| neutron | 0 | 0 | 1.67×10−27 | 1 |
| electron | −1.6×10−19 | −1 | 9.11×10−31≈0 | ≈0 |
All particles of normal matter, such as protons, neutrons and electrons have a corresponding particle that:
1.has the same mass as the normal particle
2.has opposite charge (if the normal particle is charged)
3.will undergo annihilation with the normal particle if they meet
ANTIPROTON
An antiproton is negatively charged proton.
POSITRON
This is a positively charged electron. The expression ‘anti-electron’ is not used.
ANTINEUTRINO
The antineutrino produced in beta-minus decay.
•When a particle and its corresponding antiparticle meet together annihilation occurs.
•All of their mass and kinetic energy is converted into two photons of equal frequency that move off in opposite directions.
•The opposite of annihilation.
•The energy of one photon can be used to create a particle and its corresponding antiparticle.
•The photon ceases to exist afterwards
The electon-volt (eV) is a very small unit of energy equal to 1.6×10−19J
The electron-volt is equal to the kinetic energy gained by an electron when it is accelerated by a potential difference of one volt.
Using Einstein’s relation E = mc2 the energy equivalent of mass can be calculated. The masses of sub-atomic particles are commonly quoted in energy terms using the unit MeV.
Example: the mass of a proton is 1.67×10−27 kg
E = mc2 = (1.67 x 10-27 kg) x (3.0 x 108 ms-1)2
= 1.50 x 10-10 J
This is normally expressed in terms of MeV
where 1 MeV = 1.6 x 10-13 J
And so the mass-energy of a proton in MeV
= (1.50 x 10-10 J) / (1.6 x 10-13 J)
= 938 MeV
