Radiation Interaction with Matter

Abstract

When radiation interacts with matter, it deposits energy by different interaction processes. The deposition of energy is characterised as radiation dose, and if it occurs in the living tissue of individuals, the end point effect may be the biological effect. The radiation energy deposition in absorbing medium is defined by fundamental mechanisms. These mechanisms are responsible for characteristics of the shielding, the dosimetric materials, the human organs and the radiation detectors. Various types of radiations are emitted from different types of the radionuclides. The radiations are charged particles (electron, alpha, fission products and heavy charged particles) and uncharged radiations (X-/gamma-rays and neutrons). The charge particles interact with electrons and positive charge nucleus through the Coulomb interaction during transportation. The radiation interaction results in full or partial transfer of incident radiation to electrons, nuclei of atoms or produces charged and uncharged particles. The uncharged radiation sometimes doesn't interact with the medium. In this chapter, we will briefly discuss alpha, beta, gamma-ray and neutron interaction with matter. 3.1 ALPHA INTERACTION Alpha particle is a helium nucleus (+2 charges) which interacts with the medium through the Coulomb force and ionize it. The mono-energetic alpha particles are emitted with several MeV of kinetic energy, typically 4 to 10 MeV. The alpha particles are emitted from heavy nucleus. The attractive Coulomb force works between orbital electrons and alpha when these particles enter into any medium. This interaction of electron and alpha excite or ionize the atom. This energy transfer in excitation or ionization reduces the velocity of alpha particle after each interaction. The maximum energy that can be transferred from alpha particle of mass, m and energy, E to electron of mass, m 0 in a single collision is 4Em 0 /m or about 1/500 of alpha energy per nucleon. The alpha particle interacts simultaneously with large number of electrons until it is stopped. The range of the alpha particle in most absorbing media is of order of micrometers and in air is in range of few centimeters. The range of alpha particle in standard air is an empirical fit [19] and is given by a relationship of energy, E (in MeV) and range, R (in cm) as;) 1. 3 (325. 0 2 / 3                     E R The alpha particles have same range in one medium except for some straggling about a mean range,  R.The straggling is statistical and forms a normal distribution about the mean range  R. The range of alpha particle is being used to determine its range in any other medium by the Bragg-Kleeman rule as:) 2. 3 (                  a a a m M M R R   where m R is range (in cm) in an medium, a R is range (in cm) of alpha particle in air, m  is the density of the medium, and M is the atomic weight of the medium.