WHat do mean by the term annihilation and pair production

Asked by  | 29th Jul, 2008, 03:39: PM

Expert Answer:


The photoelectric and Compton effects represent two mechanisms of photon absorption, the process in which a photon gives up some or all of its energy to a material particle (contained usually within an atom in a solid). Photon absorption can be quantified in terms of an absorption coefficient m ,commonly expressed in units of m^-1 or cm^-1 and defined by the eq uation:

I(x) = I(0) exp(-(mu) x)where I(0) and I(x) are the photon intensities (W/m^2) at the entrance surface and at a depth x below the surface (measured in the direction of the incident beam).

The eventual rise in (mu) indicates that a third process occurs at high photon energy; this is pair production, in which a pair of elementary particles (a particle and its antiparticle of the same mass but opposite electrostatic charge) are created from the energy (hf) of the original photon. In this case, the two particles are an electron and an antielectron (more commonly known as a positron, whose rest mass m0 is the same as that of an electron but whose charge is +e ).

There exists an inverse process to pair production called pair annihilation, in which a particle and its antiparticle collide and annihilate each other, the total energy of the two particles appearing as electromagnetic radiation. In the case of an electron and positron, the energy balance can be represented as:

2m0c^2 + K(-e) + K(+e) = 2 hf

Answered by  | 29th Jul, 2008, 06:30: PM

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