CHAPTER 8:
RADIOACTIVITY
TEACHER MARNI BINTI YUSUF
SMK SULTAN BADLISHAH
8.1 – DISCOVERY OF RADIOACTIVITY
History of radioactivity
 In 1895, Wilhelm Conrad Roentgen discovered X-ray.
 In 1896, discovered Radioactivity.
 Found rays emitted from the nucleus of uranium can blacken
a photographic plate even in the dark.
 In the end of 1897, Successfully detected radioactive
beams through ionization power rather than through
photographic effects.
 By April 1902, Successfully extracted 2 radioactive elements
from uranium ore namely polonium and radium.
In 1895, Wilhelm Conrad Roentgen discovered
X-ray.
Marie dan Pierre Curie
In the end of 1897, Successfully detected radioactive
beams through ionization power rather than through
photographic effects.
By April 1902, Successfully extracted 2 radioactive
elements from uranium ore namely polonium and
radium.
Polonium
Antoine Henri Becquerel,
In 1896, discovered Radioactivity.
Found rays emitted from the nucleus of
uranium can blacken a photographic plate
even in the dark.
Radioactive Substances
Radioactivity: is a random and spontaneous decay process
of an unstable nucleus by emitting radioactive radiation
Radioactive Decay
Radioactive decay is a process where an unstable nucleus emits
radioactive radiation until the nucleus become more stable.
Radioactive decay is a random and spontaneous process without
being affect by physical factor such as pressure, temperature,
chemical changes and force.
Radioactive
Decay
Unstable
nucleus for 1
radioisotope
Atom
New Nucleus that
is more smaller
and stable
Gamma Ray
Alpha Particles/
Radiation (ά)
Positive charged
Same as Helium
nucleus
Negative charged
 No charge/ neutral
Same as electron
 electromagnetic
waves
+ energy
A-nombor jisim/RAM
Z-Atomic Number
+ Energy
+ energy
+ energy
PRACTICE :
+ energy
+ energy
+ energy
+ energy
A-nombor jisim/RAM
Z-Atomic Number
+ energy
+ energy
PRACTICE :
+ energy
+ energy
A-nombor jisim/RAM
Z-Atomic Number
PRACTICE :
Decay of cobalt -60*
Decay of Radon - 222
Radon gas decays into solid polonium through
emitting an alpha particle
Units of radioactivity
Units of radioactivity
Curie (Ci)
 rate of unstable nuclei
decay
 1 Ci = 3.7 X 1010 decay/s
Becquerel (Bq)
 1 decay per second
 1 Bq = 1 decay/s
Relationship between Becquerel
and Curie
1 Ci = 37000000000 Bq
1 Bq = 2.7027027027027 x 10-11 Ci
Example:
convert 15 Bq to Ci:
15 Bq = 15 × 2.7027027027027 x 10-11 Ci
= 4.054054054054 x 10-10 Ci
Half-life of Radioactive Decay
• Half-life T½, is the
time taken for the
number of
undecayed nuclei to
be reduced to half of
its original number
(value).
Masa yang diambil untuk suatu bahan radioisotop mereput menjadi
separuh daripada jisim asalnya disebut setengah hayat (half-live).
Half-life of Radioactive Decay
For safety, the
half life for
radioactive
substances must
be short.
Decay Curve
Half-life of Radioactive Decay
Nuclei decay of radioactive element with
half-life of 5 days
Example 1
Example 2
Example 3
Formative Practice 8.1
Summative Practice 8 Page 252 (No 1 & 4)
Summative Practice 8 Page 252 (No 1 & 4)
Module 155-156
Module 155-156