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Page 1

10.1 NUCLEUS OF AN ATOM

Describe the
composition
of the
nucleus of an
atom in terms
of protons
and neutrons



Matter is made up of very small particles called
atoms

Each atom has a very small and very dense core
called nucleus. Most of the mass of atom is
contained in the nucleus

The electrons move in orbits around the nucleus.
There are a lot of empty spaces within atom
A nucleus consists of a number of protons and

neutrons.
Protons and neutrons also known as nucleons.
A proton has a unit positive charge.
A neutron is an uncharged particle of about the

same mass as the proton.
An atom is neutral because it contains an equal

number of negatively charged electrons. So the net
charge is zero.

Define proton
number (Z)

Proton number, Z, is defined as the number of protons
in a nucleus
The number of electrons = the number of protons
An element is identified by its proton number

Define
nucleon
number (A)


Nucleon number, A is defined as the total number of
protons and neutrons in a nucleus.

Number of neutrons, N = A - Z

What is
nuclide

A nuclide is an atom of a particular structure. Each
element has nucleus with a specific number of
protons.

Nuclide
notation XAZ


Proton p
1
1



Neutron n
1
0



Electron e01

A
X A = nucleon number
Z Z = proton number
X = chemical symbol of the element
Example C

12
6

Proton number of carbon = 6, carbon nucleus has 6
protons. The nucleon number of carbon is 12. So the
number of neutrons in carbon nucleus is 12 – 6 = 6


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Page 2

Define
Isotopes

Example:
H11 hydrogen


H21 deuterium


H31 tritium

Isotopes are atoms with the same proton number but
different nucleon number.
Isotopes of an element contain the same number of

protons and the same number of electrons. So
isotopes have the same chemical properties
chemical reactions involve the electrons in an
atom.

However they have different physical properties
because their mass is different.

Some isotopes exist naturally. Isotopes can also
be made artificially.




10.2 RADIOACTIVE DECAY

State what
radioactivity
Is







Radioactivity
random

process
spontaneous

process

3 different
types of
radiation


Radioactivity is the spontaneous and random
disintegration (decay) of an unstable nucleus
accompanied by the emission of energetic particles
or photons.

The nuclei of some atoms are unstable. The

nucleus of an unstable atom will decay to become
more stable by emitting radiation in the form of a
particle or electromagnetic radiation.


Random process means there is no way to tell

which nucleus will decay, and cannot predict
when it is going to decay.

A spontaneous process means the process is not
triggered by any external factors such as
temperature of pressure.

Alpha
Beta
Gamma radiation






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Page 11

(b)Thickness control
A radioactive sends

radiation through the sheet
material as it comes off the
production line. Beta
radiation are used for thin
sheets. A radiation
detector on the other side
of the sheet measures the
intensity of the radiation
passing through the sheet.

The amount of radiation
received by the detector
depends on the thickness
of the rubber sheet.




If the sheet is too thin, the reading

of the detector increases.
A signal is sent from the roller

control to the rollers so that the
pressure on the sheets can be
reduced.

(c) detecting leaks in
underground water pipes.

A radioactive substance
which emits beta particles
is added to a fluid in a
pipeline to measure the
flow rate in the pipeline
and to find leaks.

The radiation produced by
the radioactive substance
can be detected with a GM
tube counter placed above
ground.




A larger increase in the count rate

will indicate that there is leak in
that area.

Medicine
(a) Radioactive tracers
Nuclear medicine is a

branch of medicine that
uses radiation to provide
information about the
function of the specific
organs of a patient or to
treat disease.

A radioisotope is taken in by a
patient through the digestive
system, by inhalation or through
the blood vessels by injection.

The radiation emitted enables
organs such as thyroid, bones,
heart, liver to be easily imaged by
imaging equipment. Disorders can
then be detected.

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Characteristics of
radioisotope:
(a) half-life is medium,

long enough to
examine metabolic
processes in the body
and short enough to
minimize the radiation
dose to the patient.



(b) emits low energy gamma rays
which can pass through the
body without much ionization of
the molecules.



(b)Sterilizing
medical instruments are

sterilized after packing by
a brief exposure to gamma
rays.

Gamma rays can be used
to kill bacteria, mould and
insects in food.

(c)cancer treatment
Gamma rays can kill living cells.

They are used to kill cancer cells
without having to resort to surgery.

This is called radiotherapy.
It is important to administer the

correct dosage. Excessive
radiation will damage too many
healthy cells. Insufficient radiation
will not stop the cancer from
spreading.


Application of radioisotope in
the field of agriculture
By measuring the

radioactivity of the stem
and leaves, scientists can
find out how much
fertilizer has been
absorbed by the plant.

Radioisotopes are used to
kill pests and parasites
and to control the ripening
of fruits.

Application of radioisotope in
archaeology
Carbon-14 is a radioisotope with a

half-life of 5730 years and decays
by emitting beta particles.

Living animals and plants have a
known proportion of carbon-14 in
their tissues which remains
constant.

When living things die, the amount
of carbon-14 in their body
decreases at a known rate.

The amount of carbon-14 left in a
decayed plant or animal can be
used to tell its age.




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Page 22

Eating, drinking, applying cosmetic or storing food
is prohibited.

All work surfaces and storage areas should be
covered with absorbent material to contain
radioactive material contamination.

When using radioactive liquids, plastic or metal
trays (stainless steel washes easily) should be
utilized to contain potential spills.

Radioactive material, especially liquids, should be
kept in unbreakable containers whenever possible.
If glass is used, a secondary container is necessary

Before eating or drinking, wash hands and forearms
thoroughly.

Stronger radioactive sources should be handled
with robotic control systems behind steel, concrete,
lead or thick glass panels.

Radiation badges containing photographic film
should be worn to monitor exposure to radiation.
The film is regularly developed. The darkness of the
film shows the level of exposure to radiation.


Describe the
management
of
radioactive
waste



Low level
waste:









In a nuclear reactor, a very large amount of energy is
produced from a very small amount of fuel. However,
much of the waste is radioactive and therefore must be
carefully managed as hazardous waste.
Radioactive waste consists of a variety materials
requiring different methods of management to protect
people and the environment.

Comprises 90% of the volume but only 1% of the

radioactivity of all radioactive waste.
Generated from hospitals, laboratories and industry,

as well as the nuclear fuel cycle.
Comprises paper, rags, tools, clothing, filters
Contains small amounts of mostly short-lived

radioactivity
Buried in shallow landfill sites.
Often compacted or incinerated (in a closed

container) before disposal to reduce its volume.

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Page 23

Intermediate
level waste:


Makes up 7% of the volume and has 4% of the

radioactivity of all radioactive waste.
Contains higher amounts of radioactivity and may

require special shielding
Comprises resins, chemical sludge, reactor

components and contaminated material from reactor
decommissioning

Solidified in concrete or bitumen for disposal
Short-lived waste (mainly from reactors) is buried.
Long-lived waste (from reprocessing nuclear fuel) is

disposed deep underground

Consists of only 3% of the volume of all radioactive

waste but it holds 95% of the radioactivity.
Mainly used fueled rods or liquid waste from fuel

processing
Contains highly-radioactive fission products and

some heavy elements with long-lived radioactivity.
Generates large amount of heat and requires

cooling, as well as special shielding during handling
and transport.

Vitrified by incorporating it into borosilicate glass
which is sealed inside stainless steel containers for
eventual disposal deep underground.




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