Radiation Sciences: Fundamental Concepts

MEANING OF RADIATION SCIENCES

Medical radiation science is the study and application of radiant energy in the diagnosis, treatment and follow-up care of injuries and disease.

The applied medical radiation sciences encompass a number of disciplines, each distinguished by a distinctive combination of the radiation used and the associated advanced technology required to deliver and interpret the effects of the radiation.

Is a science that create, disseminate and apply scientific knowledge to improve human health.

Radiation Sciences: Fundamental Concepts

Some everyday examples are microwaves television, light, and x-rays used to cook food, radio waves for radios and used in medicine.

Important factors in this subject are;Radiation,Radioactivity and Ionization.

Radiation is the emission of energy traveling in the form of particles or waves in bundles of energy called photons .

Module Outline

• Atomic structure
• Basic interactions between X-Rays and matter.
• Classical laws.

Electromagnetic Radiations

• Radiation units and Radiation Protection.
• Radiation monitoring.

Radiobiology.

ATOMIC STRUCTURE

Learning objectives.

• By the end of this session students should be able to;
• Define atom,nucleus and shell.

Describe atomic structure and types of electrons.

Introduction

• Atom is the smallest unit of matter that define the chemical element.
• Atom made up of two main parts, that are,
• Nucleus: contains positive protons (p) and neutral neutrons (n)

Shells: Contain electrons (e) that circles the nucleus in their energy level

Nucleus

• Nucleus is the central part of an atom where almost the mass of an atom is present.
• Nucleus is composed of two main particles.
• Proton
• Neutron

Protons are positively charged particle present in nucleus.

Proton have a mass of 1.6726×10−27 kg. That is, they weigh 1,836 times the mass of electrons.

Nucleus

• Neutrons are charge less particle present in a nucleus of an atom.
• Neutron have a mass of 1.6929×10−27 kg. that is, they weigh 1,839 times mass of electrons

Both protons and neutrons in a nucleus of an atom are called Nucleons.

Nucleus

The number of protons present in nucleus of an atom is called Atomic number. And is denoted by a letter ‘Z’.

The total number of protons and neutron in a nucleus of an atom is called Mass number. And is denoted by a letter ‘A’.

Shell

Shell is an orbit that consist of an electron(s) which evolves around the nuclear of an atom.

• Shell are also known as Energy level.
• Electron is negatively charged particle that revolves on its orbit around the nucleus.
• Electron has a mass of 9.11×10−31 kg.

Each shell (orbit) has its maximum carrying capacity of electron.

Atom

Shell

• The capacity of shell to carry the electrons is determined by the formula.

2n2 where n is the number (position) of shell from nuclear.

The number of shells are numbered from the inner most shell to outer ward from the nuclear.

The inner most shell are numbered as one (n=1) and others are continuously numbered in a sequence.

Shells are also named as K, L, M, N

Shell

Types of Electrons

Electrons are either bound or free.

Bound electrons: These are the electrons that are held in orbit around the nucleus in the electron shells by the attractive force of the positive nucleus.

The binding energy is the positive energy required to overcome the pull of the nucleus and release the electron from the shell.

This is of the same magnitude as the actual (negative) energy of the electron that is released if the electron is freed.

Types of Electrons

Free electrons: These are the electrons that are not bound in an electron shell around a nucleus.

• They have a kinetic energy of:
• Kinetic energy = ½mv2

where: m = mass v = velocity

The actual binding energy of electrons is expressed in electron volts (eV) or keV (1keV = 1000 eV) 1 eV = 1.6022 x 10 -19 joules

Radiation Sciences: Fundamental Concepts

Increase in the atomic number = increase in the binding energy of the electrons (there are more protons and, therefore, more energy is needed to release the electrons from the greater positive pull).

Increase in the distance between the nucleus and the electron = decrease in the binding energy of the electron (decrease in the positive pull of the protons in the nucleus)

Atom

The number of the proton and electron in an atom is equal, thus, this make the atom to be electrically neutral.

If either number of proton or electron exceed in an atom, it become electrically charged and is called an Ion.

• If proton exceed electron it become positively charged. And the atom is named Cation.

And if electron exceed it become negatively charged. And the atom is named Anion.

Atom

The number of proton in an atom determine it’s chemical element properties since each element has it’s own number of proton.

For example hydrogen atom has only one proton in its nucleus, while Sodium atom has eleven protons in its nucleus.

If the number of proton changed in the nucleus of an atom that atom changes its chemical element properties.

Atom

Atom of an element become charged by either losing or gaining electron on its outer most shells.

Atom if gain extra electron it become negatively charged. And if loses the electron it become positively charged.

The process of either gaining or losing of electron in an atom is called Ionization.

Ionization

Atom

The atom of the same chemical element is said to have the same number of neutrons in its nucleus.

But there are occasion where the number of neutrons in atom of the same chemical element differs.

If the number of neutrons in atoms of the same chemical element differs these atoms are called Isotopes.

Atom

Isotopes are atoms of the same chemical element that have different number of neutrons in its nucleus.

For example cobalt-60 atoms and cobalt atoms.

Both radioactive cobalt-60 atoms and cobalt atoms have 27 protons but cobalt-60 atoms have 33 neutrons, instead of 32 neutrons which are present in a stable cobalt atoms.

Carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons.

Isotopes

Atom

Isotones are atoms (nuclides) having the same number of neutrons but differ proton number. Example boron-12 and carbon 13 both contain 7 neutrons.

Isobars are atoms (nuclides) of different chemical elements having the same atomic mass (number of nucleons). Example 40S, 40Cl, 40Ar, 40K and 40Ca.

Isobars

Isotones

Key Points

• Atom is the smallest unit of matter that defines a chemical element.
• Nucleus consists of protons and neutrons
• Shell is an orbit constisting of electrons evolving the nucleus of an atom.

Types of electrons are bond and free electrons.