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.