PHYSICAL BACKGROUND ATOMIC STRUCTURE, NUCLEONS AND ACTIVITY

DR. MOHAMMED MOSTAFA EMAM

INAYA MEDICAL COLLEGE (IMC)RAD 243- LECTURE 1

TOPIC

ISOTOPESRADIOISOTOPESRADIOACTVE DECAYHALF LIFE

INTRODUCTION

• INTRODUCTION ABOUT RADIATION:

Radiation is energy in the form of waves or streams of particles.

Based on the interaction with the matter there

are two types of radiation

1. Ionizing radiation 2. Non- ionizing radiation

TYPES OF RADIATION

ATOMS• Where all matter begins?

Atoms are the basic building blocks of the all the matters in this world.

All things both living and non living begins with atoms only.

Atoms are elements like oxygen , hydrogen and carbon.

STRUCTURE OF AN ATOM

Proton

ISOTOPES• An isotopes is a variant of a particular

chemical element.• Isotopes of an element consists of a same

number of protons and different number of neutrons.

• For example, hydrogen has 3 isotopes:Hydrogen 1 : 1 proton and no neutronsHydrogen 2 : 1 proton and 1 neutronHydrogen 3 : 1 proton and 2 neutrons

Isotope is stable when it has a same number of neutrons and protons.

The number of protons present in atom is called as Atomic Number.The number of protons and neutrons present in atom is called as Nuclear Number.

RADIOISOTOPEDEFINITION: • Radioactive isotope or radioisotope, natural or

artificially created isotope of a chemical element having an unstable nucleus that decays emitting α, β and ϒ rays until stability reached.

• A radioisotope is an isotope of an element that undergoes spontaneous decay and emits radiation as it decays.

• During the decay process , it becomes less radioactive overtime, eventually becoming stable.

• Once an atom reaches a stable configuration, it no longer gives off radiation.

RADIOACTIVE DECAY• Radioactive decay is the process in which an

unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

• There are two forms of radioactive decay Natural radioactivity Artificial radioactivity

RADIOACTIVE DECAY• Natural radioactivity: This is the spontaneous disintegration of

naturally occurring radio–nuclides to form a more stable nuclide with the emission of radiations of alpha, beta and gamma.

• Artificial radioactivity: This is the spontaneous disintegration of a

nuclide when bombarded with a fast moving thermal neutron to produce a new nuclide with the emission of radiations of alpha, beta and gamma and a large amount heat.

RADIOACTIVE DECAY• There are three types of radioactive emission:

α decayβ decayϒ decay

RADIOACTIVE DECAY

RADIOACTIVE DECAY

Proton mass ≈ Neutron mass

= 1 Atomic Mass Unit

RADIOACTIVE DECAYα – decay:• Alpha particles consists of large mass. Alpha

decay occurs when the atom ejects a particle from the nucleus, which consists of two neutrons and two protons.

• When alpha decay occurs, the atomic number decreases up to 2 and the mass decreases by 4 and electrical charge of +2.

RADIOACTIVE DECAY

• Another example:

RADIOACTIVE DECAYβ – decay: β particles are consists of small mass and -1

electrical charge. It is mainly emitted by nucleus.

In basic β – decay, a neutron is turned into a proton and an electron is emitted from the nucleus.

The atomic number increases by 1 and mass decreases slightly.

RADIOACTIVE DECAYϒ – emission: Gamma radiation have high energy, short

wave length. It accompanies with alpha and beta emission, but it’s usually not shown in a balanced nuclear reaction.

Gamma is an electromagnetic wave or photon which has no electrical charge and has great penetrating power.

Gamma decay takes place when there is residual energy in the nucleus following α or β decay.

RADIOACTIVE DECAY• The residual energy is released as a photon of

gamma radiation. Gamma decay generally does not affect the mass or atomic number of a radioisotope.

• Gamma radiation is similar to that of X- rays.

• E.g., Cobalt- 60(Co-60). Gamma rays are focused on the tumor to destroy it.

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HALF LIFE

• Radioactive half-life is the time it takes half the radioactive atoms present to decay.

Before After one half-life

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