Page 179 - Physics 10_Float

ATOMIC AND NUCLEAR PHYSICS

photons. They are electromagnetic radiations of very high
frequency (short wavelength) emitted by the unstable lons
excited nuclie.

Ionizing Effect
The phenomenon by which radiations split matter into
positive and negative ions is called ionization. All three
kinds of radiations i.e., alpha, beta and gamma can ionize -particle Neutral gas
molecules
the matter. However, alpha particles have the greatest
power of ionization as compared to beta particles and Alpha particles cause
intense ionization in
gamma rays. It is due to large positive charge and large mass (a)
a gas
of alpha particles. Beta particles ionize a gas much less than
alpha particles. The ionization power of gamma rays is even
less than that of beta particles. Ionization of three lons
radiations in a gas is shown in Fig. 18.5.

Penetrating Ability
The strength of radiations to penetrate a certain material is
called penetrating power. The alpha particle has the
-particle
shortest range because of its strong interacting or ionizing
power. The gamma rays can penetrate a considerable Beta particles ionize a
thickness of concrete. It is due to their large speed and gas much less than alpha
particles
neutral nature. (b)
The beta radiation strongly interacts with matter due to its
charge and has a short range as compared to gamma  -ray
radiations. Fig. 18.6 shows the relative penetrating abilities
of three kinds of radiations.
Paper Lead
Alpha
particle
Beta
particle
Gamma
particle

Radioactive source Gamma rays ionize a
gas even less than beta
Aluminium
particles
Fig.18.6: Penetrating power of radiations in different materials
Alpha particle has a range of only a few centimetres in air.
Beta particles have range of several metres in air. Fig. 18.5: Ionization effect of
radiations in a gas
However, gamma rays have a range of several hundreds
metres in air.

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