Radioactive decay occurs when an unstable nucleus spontaneously disintegrates by emitting particles or electromagnetic waves. There are three main types of radioactive emissions: alpha particles, beta particles, and gamma rays. Each type has distinct properties in terms of charge, speed, penetrating power, and interaction with electric and magnetic fields. Radioactive decay continues in a nucleus until it reaches a stable configuration. The rate of decay is random but consistent, allowing the calculation of half-life, the time for half the radioactive nuclei to decay. Common radioactive isotopes and their half-lives are listed.

1. RADIOACTIVE
DECAY
by : azyulail azra

2. radioactivity
particles
emission of
energetic
The spontaneous
disintegration of
an unstable nucleus
photons
• cannot be detected.
• energetic enough to knock electrons
out of the
atoms of a medium to produce ions.
• also known as
ionising radiation.

3. radioactive emissions
α-particles
helium nucleus
γ-rays
electromagnetic
waves

4. differences
α-particles β-particles
Charge
Positive
charge
Speed
Up to 10% Up to 99% Speed of
of speed of of speed of light
light
light
Nuclide
notation
4
He
2
Negative
charge
γ-rays
0
-1
e
No charge
(neutral)
-

5. Penetrating
power
γ-rays
α-particles β-particles
# Average # High
# Low
# Stopped by # Stopped by
a few
a sheet of
millimeters of
paper
aluminium
# A few
centimeters
of lead can
absorb a
significant
amount of it

6. α-particles β-particles
Effect of
magnetic
field
Small
deflection
γ-rays
Large
No
deflection deflection
in the
opposite
direction of
the αparticles

7. α-particles β-particles
Effects of
electric
field
Small
Large
deflection
towards
negatively
charged
plate
deflection
towards
positively
charged
plate
γ-rays
No
deflection

8. α-particles β-particles
Range
in air
Several
centimetres
Several
metres
γ-rays
Several
hundred
metres
Tracks in Straight
and thick
cloud
chamber lines
Thin and Very fine
wavy lines short lines
Ionising
power
Medium
Strong
Very weak

9. radioactive detectors
Cloud chamber
Photographic Film
Geiger-Muller Tube
Spark counter

10. cloud chamber
- to show
the path of ionizing radiation.
- formed in the same way as the
condensation trails behind
a high-flying aeroplane

11. α - particles
β - particles
γ - rays

13. photographic film
- Found in badges worn by the staff at
radiation laboratories

14. GM tube
Radiation
Enters through
mica window
240 V
Ionizes
argon gas
Pulse of
current
produced
Pulse of current
counted using
ratemeter/scaler
Number of
counts
period of time

16. spark counter
Suitable for alpha rays
ionizes
the air
between the
gauze and the
wire
radioactive
source is
brought near
sparks
are produced

17. radioactive decay
• Nuclei that have too
few or too many neutrons are
unstable.
the process of a nucleus changing to a
more stable nucleus while emitting
most likely to be
•
radiation.
• Nucleus before the decay = parent
product of the decay
•
•
nuclide
= daughter nuclide.
The daughter nuclide may still be unstable and will eventually decay into another
nuclide.
This process continues until a stable nuclide is reached.

18. Alpha decay
-This type of decay usually
happens to the heavier
unstable nuclei.
-The proton number is reduced by
2 while the nucleon number is
reduced by 4 and emit αparticles
238
92
U
238 – 4 = 234
92 – 2 = 90
Th +
4
2 He

19. 14
6C
14 - 0 = 14
N
6 - (-1) = 7
+
0
-1
e
Beta decay
-Beta decay usually occurs
for nuclei that have
an
excess of
neutrons.
- There is no change in
the nucleon number but the
proton number increases by 1
and emit β-particles

20. Gamma decay
-occurs when an unstable nucleus
releases its excess energy [ high
frequency electromagnetic
waves ] called γ-rays.
-no change in proton number and
nucleon number but emit γ-rays
-A nucleus that undergoes alpha or beta
decay may
60
Co
27
also emit γ-rays.
60
27
Co +
γ

21. half-life
• Time taken for undecayed nuclei to be
reduced to half of its original number
• The number of unstable nuclei have not
decayed decreases with time.
• The half-life constant ~ the decay process
is random and large.

22. 128
64
Original number of
undecayed nuclei
= 256
Half of original number = 128
It takes 3 hours for the
undecayed nuclei to be reduced
to half of original number.
∴ 1 half-life = 3 hours

23. Radionuclide
Half-life (T1/2)
90Sr
Strontium-90
28.5 years
137Cs
Caesium-137
30.1 years
226Ra
Radium-226
1600 years
14C
Carbon-14
5736 years
40K
Potassium-40
1.28 x 108
years

24. Thank
you !!!