Interaction of Radiation with Matter

MATTER

ATOM An Atom can be defined as the smallest quantity of an element which can enter into a chemical reaction. All atoms of a particular element are chemically alike but they differ from the atoms of other elements. The atom is a basic unit of matter.

BASIC MODEL OF ATOM Electrons(-) orbiting nucleus of protons(+) and neutrons. Same number of electrons as protons; net charge = 0. Atomic number (number of protons) determines element. Mass number (protons + neutrons) gives mass in terms of 1/12th mass of Carbon atom.

ELEMENT An Element is a substance which cannot be split up into two or more simpler substances by the usual chemical methods of applying Heat, Light or electric energy. An is made up of atoms. All having same atomic number.

RADIATION Non- Ionizing Types of Radiation Ionizing Radiation is an energy in the form of electro-magnetic waves or particulate matter, traveling in the air. OR The term radiation applies to the emission and propagation of energy through space or a material. Types of Radiation Ionizing Non- Ionizing

Basic Concept of Interaction Three possible occurrences when x or gamma photons in the primary beam pass through matter: No interaction at all Known as transmission Absorption Scatter The latter two are methods of attenuation

NUCLEAR INTERACTION Forces: There are many interactions among nuclei. It turns out that there are forces other than the electromagnetic force and the gravitational force which govern the interactions among nuclei. Einstein in 1905m showed 2 more laws: energy/mass, and binding energy

IONIZATION RADIATION Electromagnetic Particular X-rays (produced extra-nuclearly) γ-rays (produced intra-nuclearly) Electrons Protons α-Particles Neutrons Deuterons Heavy charged particles

ELECTRMAGNETIC SPECTRUM The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.

Like X-rays, radio waves, radar, radiant heat, laser and visible light are forms of electromagnetic radiation. They have the same velocity but different wavelengths. For example, radio wave have a wavelength of 300m; visible light - 5x10-5; X-rays - 1x10-8cm.

ELECTRMAGNETIC SPECTRUM An

Electromagnetic Spectrum

Electromagnetic Spectrum

ELECTRMAGNETIC RADIATION Electromagnetic radiation (EM radiation or EMR) is a form of energy emitted and absorbed by charged particles which exhibits wave-like behavior as it travels through space. EMR has both electric and magnetic field components.  In a vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.

General Characteristics of EMR no mass or physical form travel at speed of light (c) in a vacuum (or air) c = 3 x 108 m/s travel in a linear path (until interaction occurs) unaffected by electric or magnetic fields gravity

Contd… obeys the wave equation c =  In Passing through the matter, the intensity is reduced (attenuation), because of absorption & scattering. obeys the inverse square law I1d12 = I2d22 Radiation intensity is inversely proportional to the square of the distance from the source at any place.

Contd…. In passing through matter, the intensity of the radiation is reduced (attenuation), both because some radiation energy is taken Up by material (absorption) and some is deflected from its original path to travel in a new direction (scattering). It should be noted that any effect of radiation on matter depends on how much energy that matter receives (absorbs) from the beam

Types of Radiations Ionizing Radiation Non-ionizing Radiation Two types of Radiation: Ionizing Radiation Non-ionizing Radiation

IONIZING RADIATION Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because they have an excess of energy or mass or both. Unstable atoms are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation.

NON-IONIZING RADIATION They are electromagnetic waves incapable of producing ions while passing through matter, due to their lower energy.” It has not enough energy to pull electron from orbit, but can excite the electro.

NON-IONIZING Vs IONIZING Radiation that has enough energy to move atoms to vibrate, but not enough energy to remove electrons. The process by which a neutral atom acquires a positive or a negative charge is known as Ionization. Removal of an orbital electron leaves the atom positively charged, resulting in an ion pair. molecule with a net positive charge free electron with a negative charge

Primary Types of Ionizing Radiation Alpha Particles Beta Particles Gamma Rays (or Photons) X-Rays Neutrons

Radioactive Atom Ionizing Radiation alpha particle beta particle X-ray gamma ray

ALPHA PARTICLES Alpha Particles: emitted from the nucleus of an atom have 2 neutrons and 2 protons They travel short distances, have large mass. It is identical to the nucleus of a Helium atom, without the electrons. Only a hazard when inhaled.

BETA PARTICLES Beta Particles: Electrons or positrons having small mass and variable energy. Emitted from the nucleus of an atom. Electrons form when a neutron transforms into a proton and an electron.

GAMMA RAYS Gamma Rays (or photons): are Electromagnetic waves / photons. Releases energy, usually after an alpha, beta or positron transition Emitted from the nucleus (center) of an atom. Have higher energy in MeV’s.

PENETRATION POWER

X-RAYS X-Rays: are photons Electromagnetic waves and photons. Emitted from electron orbits. X-rays have energy in KeV‘s.