RADIOACTIVITY

RADIOACTIVITY
Key notes:
1. Alpha-particles are helium nuclei, have strong ionizing power, are stop by a
piece of paper and are deflected by a magnetic or electric field.
2. Beta-particles are fast moving electrons, have weak ionizing power, are stop
by a few mm of aluminium and are deflected easily by a magnetic or electric
field.
3. Gamma-rays are high energy electromagnetic waves. Though their ionizing
power is very weak, they have high penetrating power.
4. A charged electroscope is an effective detector of α-particles.
5. A G-M tube connected to a ratemeter can read the count rate or rate of
radioactivity of a radioactive source.
6. In the cloud chamber, the various types of radiation can be identified from
their tracks.
7. In the absence of a radioactive source, a background count rate is obtained due
to the background radiations.
8. In the nuclear model of the atom, an atom consists of a nucleus, which made
up of protons and neutrons, with the electrons orbiting in the space around the
nucleus. The number of electrons equals the number of protons.
9. The proton number Z is the number of protons in a nucleus.
10. The nuclide is a nuclear species with a specific combination of protons and
neutrons.
11. Isotopes have the same proton number but different nucleon numbers.
12. During α-decay, the proton number decreases by two, and the nucleon number
decrease by four.
13. During ß-decay, the proton number increase by one, and the nucleon number
remains unchanged.
14. For γ-emission, there is no change in the proton number or the nucleon
number.
15. Radioactive decay is a spontaneous random process which is unaffected by
chemical conditions, temperature or other physical conditions.
16. The half-life of a radioactive element is the time taken for half the number of
atoms in a sample to decay.
17. The rate of decay or radioactivity of a radioactive sample is directly
proportional to the number of radioactive atoms present.
18. Radioisotopes are widely use in medicine, industries and agriculture.
O LEVEL PHYSICS REVISION NOTES
19. Exposure to nuclear radiation is harmful to health.
20. Precautions need to be taken in the storage, use and disposal of radioactive
materials.
21. Energy released in a nuclear reaction is due to the decrease in mass in the
reaction.
22. Nuclear fission is the splitting of a nucleus into smaller nuclei.
23. During fission of an U-235 nucleus, two or three secondary neutrons are
produced.
24. Nuclear fusion is the union of two small nuclei to form a larger nucleus.