CHAPTER 8 RADIOACTIVITY

CHAPTER 8
RADIOACTIVITY

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8.1 DISCOVERY OF RADIOACTIVITY

HISTORY OF RADIOACTIVITY
 In 1895, Wilhelm Conrad Roentgen, a German

physicist, discovered X-ray.
 He had unintentionally taken an X-ray

photograph of his wife’s hand.
 This success led Wilhelm Conrad Roentagen

to receive the first Nobel Prize in Physics in
1901 for the discovery of X-ray.

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HISTORY OF RADIOACTIVITY
 In 1896, Antoine Henri Becquerel, physicist become the first

person to successfully discover radioactivity
 He found a radioactive compound, uranium and unintentionally

produced rays that can blacken a photographic plate even in the
dark
 The rays were detected based on the ionizing property
 Antoine Henri Becquerel received the Nobel Prize in Physic in
1903 for the discovery of radioactivity

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HISTORY OF RADIOACTIVITY Marie Curie is the only
women who received two
 At the end of 1897 Marie and Pierre Curie a married couple from Nobel Prizes, the Nobel
Poland, successfully detected radioactive radiation through its ionizing Prize in Physics in 1903
power and not through the photographic effect
and the Nobel Prize in
 Beginning with uranium ore which is known as pitchblende, they Chemistry in 1911
successfully extracted two radioactive elements, polonium and radium

 Marie Curie died at the age of 67 from a disease caused by prolonged
exposure to gamma rays

 Since the discovery of radium, the gamma rays emitted by radium
have been used in various field including medicine in cancer treatment

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RADIOACTIVITY

 Is a random and spontaneous decay process of unstable nucleus by
emitting radioactive radiation
 Radioactive radiation consists of:
i. Alpha particles (alpha radiation)
ii. Beta particle (beta radiation)
iii. Gamma ray,
 Radioactive decay is a random and spontaneous process where an
unstable nucleus emits radioactive radiation until the nucleus becomes
more stable.
 Examples unstable nuclei and decay spontaneously by emitting
radioactive radiation:
i. carbon-14 (C-14) iii. Thorium-234 (Th-234)
ii. Radon-222 (Rn-222) iv. Uranium-238 (U-238)

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Three types of radioactive radiation
emitted from the spontaneous decay of

nuclei

RADIOACTIVE
RADIATION

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UNITS OF RADIOACTIVITY

 The first unit of radioactivity introduced was curie (Ci)
 The rate of unstable nuclei decay (or activity in nuclei

decay) is measured in curie
 1 curie is 3.7 x 1010 decays per second

1 Ci = 3.7 x 1010 decays/s

 The S.I unit of radioactivity is Becquerel (Bq)
 1 bacquerel (Bq) is 1 decay per second

1 Bq = 1 decay/s

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HALF LIFE OF RADIOACTIVITY DECAY

 Half-life T½ is the time taken for the number of nuclei to decay to half of
its original number

Nuclei decay of a radioactive element with half-life
of 5 days

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HALF LIFE OF RADIOACTIVITY DECAY

 Half-life T½ is the time taken for the number of nuclei to decay to half of
its original number

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HALF LIFE OF RADIOACTIVITY DECAY

Example 3

The activity of radioactive substances Q against time is shown in
Table below Time
0 5 10 15 20 25

(minutes)

Activity 120 80 56 40 28 20
(Bq)

a) Draw a graph of activity against time on a piece of graph paper
b) Based on the graph, what is the half-life of Q?

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NUCLEAR RADIATOR DETECTORS

 Radioactivity can be detected by using several instruments such as :

Radioactive radiation Detector
Beta and gamma Photography film
Alpha and beta Gold paper
Alpha, beta and gamma Cloud chamber
Alpha, beta and gamma Geiger-Muller Tube (G.M tube)

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NUCLEAR RADIATOR DETECTORS

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8.2 ATOM AND NUCLEUS

 Atom originate from the word ‘atomos’ means indivisible.
 John Dalton 1808, introduces a theory on the structure of atom
 Dalton’s Atomic Theory : an atom is the smallest particle and cannot be further divided.
 The development of science has succeeded in finding particles that are even smaller called protons,

electrons and neutrons
 When the number of protons in an atom is the same as the number of its electrons, the atom is

neutral

Negatively charged

Positively charged
Neutral
Negatively charged

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Formation of Positive Ions and Negative Ions

 When an atom loses or gains electron, the atom becomes a charged particle known as
ion

Positive Ion (Cation)

 An atom that LOSES electrons forms a POSITIVE ION (CATION)

Sodium atom, Na Sodium ion, Na+

SUBATOMIC PARTICLE NUMBER CHARGE SUBATOMIC PARTICLE NUMBER CHARGE
0 0
Neutron, n 12 Loses Neutron, n 12
+11 1 e- +11
-11 -10
Proton, p 11 0 Proton, p 11 +1

Electron, e 11 Electron, e 10

The charge on sodium atom, Na The charge on sodium atom, Na+

Formation of sodium ion, Na+

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Formation of Positive Ions and Negative Ions

Negative Ion (anion)
 An atom that GAINS electrons forms a NEGATIVE ION (ANION)

Chloride atom, Cl Chloride ion, Cl-

SUBATOMIC PARTICLE NUMBER CHARGE Gains SUBATOMIC PARTICLE NUMBER CHARGE
0 1 e- 0
Neutron, n 18 Neutron, n 18
+17 +17
Proton, p 17 -17 Proton, p 17 -18
0 -1
Electron, e 17 Electron, e 18

The charge on sodium atom, Cl The charge on sodium atom, Cl-

Formation of chloride ion, Cl-

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8.3 IONISING RADIATION AND NON-IONISING RADIATION

Ionising radiation is a radioactive radiation that
passes through the air and produces positive
ions and negative ions

Non-Ionising radiation is a radioactive radiation
in the electromagnetic spectrum which does not
have enough energy to cause ionization

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Types of Ionizing Radiation Three types of radioactive radiation which are radiation are alpha
radiation, beta radiation and gamma radiation

Types of Radioactive Alpha radiation Beta radiation Gamma ray
Radiation Helium nucleus High speed electron Electromagnetic wave

Natural characteristic

Charge of particle Positive Negative Neutral
Ionising power High Moderate Low
Penetration power

Deflection by electric field

Deflection by magnetic field

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SOURCES OF IONIZING
RADIATION

Natural Man-made
Examples : Examples :
- Cosmic rays - Nuclear accidents
- Background radiation -Nuclear tests
- Use of radioisotope for medical

purpose
- -Background radiation

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DETECT NATURAL SOURCES OF IONIZING RADIATION

• Cosmic rays are high-energy radiation
produced outside the Solar System or
from another galaxy

• These cosmic rays are also known as
galactic cosmic rays

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BACKGROUND RADIATION

• Made up of various types of ionizing radiation in the
environment

• Source of background radiation include:
i. Cosmic rays
ii. Radioactive radiation from natural radioactive

substances in the surroundings
iii. Radioactive wastes from nuclear accidents and nuclear

tests
iv. Radioisotopes from medical use

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Unit of Dose Rate Measurement for Background
Radiation

• Ionising radiation that is absorbed into human body will damage body cells
• Measured in a quantity known as DOSE
• A dose 1 Sv = 1 joule of ionizing radiation energy that is absorbed by 1 kg

of living tissue
• Unit of background radiation dose that is commonly used is

microSievert/hour (µSv/h)
• Apparatus to measured the radiation : Geiger counter

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Safe Background Radiation dose in Daily Life

• Background radiation or ionizing radiation dose of less than 0.2 µSv/h is
the normal level or safe level

Tv/computer : Smoking: Buiding : radioactive
ionizing radiation radioactive radiation 1.5mSv/year
radiation 55
Outer space : 0.01mSv/h mSv/cigarette
cosmic rays 0.35

mSv/year

Flight : cosmic rays 0.003
mSv/h

X-ray Environment: background Food : radioactive High altitude : cosmic
5.5 mSv/medical radiation 0.4 – 1.0 Sv/year radiation 0.1 – 0.5 rays 0.3 – 0.5 mSv/year
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Unit of Dose Rate Measurement for Background
Radiation

Source of ionizing radiation dose received Safety measures
Background radiation
Use appropriate protective equipment such as
X-ray spectacles fitted with anti-ultraviolet film, anti-
Television ultraviolet umbrellas and other
Food contaminated with radioactive substances
Taken under doctor’s prescription
Cosmic rays
Ensure distance between the television and the viewer
is at least 2 m

Do not eat food produced in areas contaminated with
radioactive substances such as fish from the sea
contaminated with radioactive substances

Working hours of a pilot are limited to a certain period
of time because the pilot is exposed to cosmic rays

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8.4 USES OF RADIOACTIVE RADIATION

Archeology and Geochronology:

 Carbon dioxide in the air is made up of carbon-12 (C-12)
which is stable and carbon-14(C-14) which is radioactive

 Carbon dioxide is absorbed and released by the body of
living organisms, the percentage of C-14 in the tissues
of the organisms does not change

 When the organisms die, the amount of C-14 in their
tissues begins to decline because they decay by emitting
beta radiation with half-life T½, of 5700 years

 Carbon-14 : determines the age of the organisms or
artefacts

 This method is known as carbon-14 dating

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Monitoring the Thickness of Metal
Sheets (Industry)

 The thickness control device monitors the
thickness of metal sheets in factories

 A metal sheet is passed in between a beta
radiation source and a beta radiation
detector

 If the beta radiation detector detects too
much beta radiations, this means that the
metal sheet is too thin

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AGRICULTURE

 The rate at which beta radiation is emitted
during the nuclei decay of phosphorus-32
(P-32) is used to determine the absorption
rate of phosphate fertilizer in plants

 Uses of Radioactive radiation:
i. to kill beetles
ii. control the population of pests by
sterilization
iii. determine the best type of phosphate
fertilizer
iv. modify the characteristics of plants.

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DEFENCE

 Used in the field of defence such as the nuclear bomb
 Heat, radioactive radiation released from the explosion

of a nuclear bomb destroys almost all living things

Radura logo FOOD PRESERVATION

 The Radura logo is used to label food preserved
using radiation such as gamma rays.

 Gamma rays are used to kill bacteria in the food
during preservation

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MEDICAL

 Gamma rays from caesium-137 (Cs-137) or
cobalt-60 (Co-60) : to kill cancer cells

 Sodium-24 (Na-24) : to determine the
location of blood clots

 Technetium-99 (Tc-99) : treat tumours in
the brain

 Cobalt-60 (C0-60) : destroy germs
 Iodine-131 (I-131) : treat thyroid gland

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Safe and Proper Handling of Radioactive Substances and Radioactive Waste

Storing radioactive sources or Radioactive substances are Robotic hands are used to handle
radioactive waste in containers shielded with thick slabs of lead radioactive substances safely

with thick lead walls

Detecting the dose rate of radioactive Wearing appropriate protective clothing
radiation absorbed into the body with when handling radioactive substances
detectors such as radiation badges
Disposal of radioactive waste done
safely and properly

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APPRECIATING THE IMPORTANCE OF
RADIOACTIVE RADIATION

• Grateful to almighty for creating radioactive particles that
have many uses to sustain life

• The first artificial radioactive element, phosphorus-30 (P-
30) was created by Irene Joliot-Curie, the daughter of
Marie Curie

• Artificial radioactive elements cannot be produced without
the radioactive particles

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