“Radioactive Decay” MHT-CET Class 12 Physics Crash Course| Chapter Structure of Atoms and Nuclei
In this session G.S. Khairnar will discuss the theory and MCQ’s of Radioactive Decay. The session will be useful for all the aspirants of MHT-CET 2022. The session will be in Marathi and English.
Radioactive Decay
Points to recall:
We have leant that binding energy per nucleons determines the stability of nucleus. The stability of nucleus is proportional to the B.E. per nucleons. If the B.E. per nucleus is less, the nucleus is less stable whereas the nucleus is more stable, if its B.E. per Nucleon is higher.
The B.E. curve is an indicator of nuclear stability.
According to binding energy per nucleon curve,
- The B.E. per nucleon is constant for mass number 30<A<170.
- It is maximum 8.75 MeV for A = 56 & 7.6 MeV for A = 238
- It is low for light nuclei A< 30 & heavy nuclei A < 170 which indicates that atoms are loosely bound with nucleuses.
- When heavy nucleus breaks into lighter nuclei, B.E. increases.
- When very light nuclei A < 10, join to form heavier nucleus, B.E. increases.
Let’s study concept of radioactivity…….!
Radioactivity: –
The phenomenon of spontaneous emission of radiations from radioactive substance is known as radioactive decay.
Radioactivity is nuclear phenomenon in which an unstable nucleus undergoes decay. It is called radioactive decay.
There are three types of decay,
Let’s discuss the different types of decay in detail…….!
Properties of α particles.
- They are positively charged particles. It is helium atom with both electrons removed. Its mass is 6.64 ×10 -27 kg and charge is + 3.2 ×10 -10 coloumb
- Being charged particle, it is deflected by electric and magnetic field.
- The speed of emission of – particles depend upon the nature of radioactive element.
- They affect photographic plate, produce fluorescence.
- They ionize gas when passed through gas.
- The range of α particles through air varies from 2.7 cm to 8.62 cm for thorium.
- They are scattered when incident on aluminium, Mica, and gold foil.
- When α particle is emitted by an atom, its atomic number decreases by 2 and mass number decreases by 4.
Properties of β particles.
- β – rays are fast moving electrons from nucleus.
- Their speed ranges from 1% to 99% of speed of light.
- Being charged particles they are deflected by electric and magnetic field.
- They can ionize gas but its ionization power is (1/100) th of that of α particles.
- They are more penetrating than α particles.
- Their range in air depends on their speed.β Particle of 0.5 MeV has a range of 1 m in air.
- When β particle is radiated, the atomic number increases by 1 and mass number does not change.
Properties of γ particles.
- γ-rays are not particles but they are electromagnetic waves (photons) of very short wavelength. Photons originating from the nucleus are called γ rays.
- They are neutral in charge and not affected by electric and magnetic field.
- They affect photographic plate and produce fluorescence.
- They have very low ionization power about (1/1000)th that of α particles.
- They have high penetration power and can pass through 25 cm thick iron plates.
- They are diffracted by crystals.
Radioactive Decay
Let’s solve the following multiple choice questions………..!
Q.1) During emission of – particles from radioactive atom the atomic number decreases by…
a) 1
b) 2
c) 3
d)4
Answer
b) 2
Q.2) What is the total charge on α – particles?
Q.3) Which among the following is not correct for α – particles?
a) They ionize gas when passed through gas.
b) They affect photographic plate.
c) They are scattered when incident on aluminium.
d) They are neutral hence not deflected by electric and magnetic field.
Answer
d) They are neutral hence not deflected by electric and magnetic field.
Q.4) Which among the following is correct for α – particles?
Q.5) Binding energy is maximum for mass number of……..
a) A = 01 & A = 238
b) A = 06 & A = 138
c) A = 30 & A = 170
d) A = 56 & A = 238
Answer
d) A = 56 & A = 238
Q.6) Ionisation power of beta particles is……of alpha particles.
a) (1/10)th
b) (1/100)th
a) (1/1000)th
d) same as that
Answer
b) (1/100)th
Q.7) The energy emitted in beta decay is represented as……
Q.8) Nucleus with higher binding energy per nucleon are…
a) most unstable nuclei
b) most stable nuclei
a) both ‘a’ and ‘b’
d) neither ‘a’ nor ‘b’
Answer
b) most stable nuclei
Q.9) The range of beta particle of 0.5 MeV in air is……
a) 100 m
b) 10 m
c) 1 m
d) 0.1 m
Answer
c) 1 m
Q.10) Which among the following is not true for gamma particles?
a) They possessed highest ionization power.
b) They affect photographic plate.
c) They have high penetration power.
d) They are neutral hence not deflected by electric and magnetic field.
Answer
a) They possessed highest ionization power.
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