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Monday, September 19, 2011

Physics Form 5: Chapter 5 - Ionizing Power and Penetrating Power


Type of Radiation
Alpha particle
Beta particle
Gamma ray
Symbol
α
β
γ
Mass (atomic mass units)
4
1/2000
0
Charge
+2
-1
0
Speed
slow
fast
very fast (speed of light)
Ionising ability
high
medium
weak
Penetrating power
low
medium
high
Stopped by:
paper
aluminium
lead


Alpha particle:
  • It carries +2 charge and exerts greater forces on the neighbouring air molecules.
  • It moves at a relatively low speed. The chance of ionising the neighbouring molecule is higher.
  • It has a strong ionising power and it loses kinetic energy readily to ionise the air molecules along its path. So it has absorbed in the air quickly.
Beta particle:
  • It carries -1 charge and exerts smaller forces on the air molecules.
  • It travels faster and the chances of ionising the neighbouring molecules are lower.
  • It has much weaker ionising power. So it loses kinetic energy at lower rate. Thus, it has a stronger penetrating power than alpha.
Gamma particle:
  • It is electrically neutral and travels very fast at the speed of light.
  • Ionising effects only occur when they collide directly with the air molecules. Since the chances for such a collision are very slim, gamma rays seldom produce ion pairs.
  • It is a high frequency electromagnetic wave and it possess the highest energy.
  • It has extremely weak ionising power. So it loses kinetic energy at the lowest rate.

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