Subject: Physics
A subatomic particle that has the same mass as another particle but opposite value of some other properties is called antiparticle. For example, the antiparticle of the electron is a positron, which has the same mass as that of the electron but has a positive charge equal to the proton's positive charge. The existence of antiparticles is predicted by relativistic quantum mechanics. When a particle and its antiparticle collide annihilation takes place. When an electron meets a positron the energy produced due to annihilation is 2mc2 where m is the mass of electron or positron and c is the velocity of light.
When an energetic γ-ray photon falls on heavy substance, it is absorbed by some nucleus of the substance, and its energy gives rise to the production of an electron and a positron. This phenomenon, in which energy is converted into mass, is called ‘pair-production’ and represented by following equation:
\begin{matrix} &hv &= &-1e^0 &+ &1e^0 \\ &(\gamma -\text {photon}) &&(\text {electron}) &&(\text {positron}) \end{matrix}
According to Einstein’s energy-mass relation, a body in the state of rest also has some energy, called its rest-mass energy. If the rest mass of the body be m0, then its rest-mass energy is \(E_0 = m_0c^2 \).
The rest-mass of each of the electron and the positron is 9.1 × 10-31 kg. so, the rest-mass energy of each of them is
\begin{align*} E_0 = m_0c^2 &= (9.1 \times 10^{-31} kg ) \times (3.0 \times 10^8 s^{-1})^2 \\ &= 8.2 \times 10^{-14} = \frac {8.2 \times 10^{-14}}{1.6 \times 10^{-13}} Mev = 0.51 Mev \\ \end{align*}
For pair production, it is essential that the energy of γ-photon must be at least 2× 0.51 = 1.02 MeV. If the energy of γ photon is less than this, it would cause photoelectric effect or Compton effect on striking the matter. If the energy of γ-photon is more than 1.02 MeV, then electron and positron are produced and the energy in excess of 1.02 MeV is obtain as a kinetic energy of these particles. The converse phenomenon of pair-annihilation is also possible. Whenever an electron and a positron come very close to each other, they annihilate each other by combing together and two γ-photons are produced. This phenomenon, in which mass is converted into energy, is called ‘pair-annihilation’, and s represented by following equation:
\begin{matrix}&-1e^0 &+ & +e^0 &= hv &+ &hv \\&(\text {electron})&&(\text {positron})&(\gamma-\text {photon}) &&(\gamma-\text {photon})&\end{matrix}
There are four types of forces/interactions in the nature. They are:
Reference
Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel.Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.
S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.
A subatomic particle that has the same mass as another particle but opposite value of some other properties is called antiparticle.
According to Einstein’s energy-mass relation, a body in the state of rest also has some energy, called its rest-mass energy.
The phenomenon, in which energy is converted into mass, is called ‘pair-production’
The phenomenon, in which mass is converted into energy, is called ‘pair-annihilation’,
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