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Topic 5 Nuclear decay
1.What is meant by a radioactive atom?
A radioactive isotope has an unstable nucleus which decays and emits α, β or γ radiation.
2.What is meant by Random?
We cannot know when an individual nucleus will decay and which will decay next.
In a given time interval each nucleus has a fixed probability of decay.
3.What is meant by Spontaneous?
The decay cannot be influenced by any external factors.
4.Atomic processes that produce emission spectra of X ray:
There are different energy levels for electron in atom. Electron jumps down to original state will release energy in the form of large photon energy.
5.What is the similarity and difference between popcorn kernels popping and radioactive atoms decaying?
Similarity: Both are random events. Both have decreasing rate of decay. Radioactive decay is an irreversible change, as is the corn popping.
Difference: Popping of corn depends on external factors and radioactive decay does not. The corn kernels do not emit standard fragments, while radioactive nucleus emit radiation.
6.What is half life?
The average time taken for the activity of the source to halve.
7.Why α radiation does not pose a health hazard?
α radiation only has a range of a few cm in air, and cannot penetrate wall of container or skin.
8.What are the characteristics of β radiation?
Beta particles can easily penetrate the body, since they are not very ionising.
Once inside the body beta radiation may damage DNA of cells.
Beta radiation can be absorbed by a few mm of aluminium.
9.What is binding energy?
Energy required to separate a nucleus into its component nucleons.
10.How is fusion able to release energy?
In a nuclear fusion small nuclei fuse to produce a larger nucleus. The mass of the fused nucleus is less than the total mass of initial nuclei.
Energy released ΔE = c^2 Δm
11.What are the conditions for fusion to occur and why the interiors of stars are ideal for this?
There must be a very high temperature so that protons have sufficient kinetic energy to overcome the electrostatic repulsion, and the protons can come close enough for fusion to take place.
There must be a very high density so that a sufficient collision rate is maintained.
The enormous gravitational forces acting in stars create a very high temperature and density, so it is ideal for fusion to occur.
12.What is Fission Process for nuclear power station?
A heavy nucleus absorbs a neutron,
And the nucleus becomes unstable and splits into two fragments.
A few neutrons are also emitted in the fission.
These neutrons can cause further fission.
13.What is meant by nuclear fission and why energy is released during the fission of a nucleus?
Nuclear fission is the splitting of a large nucleus into smaller nuclei.
The mass of the fission fragments is less than the mass of the original nucleus.
According to ΔE=c^2 Δm , energy is released during fission.
14.What are the advantages of fusion power over fission power?
Fuel for fusion is unlimited.
Fusion result in few radioactive products, while fission wastes have a disposal problem.
Energy released by fusion is greater than the energy released by fission.
15.What are the technical difficulties of producing a practical nuclear fusion reactor?
An extremely high temperature is required.
Plasma must not touch reactor walls, so strong magnetic fields are required.
If plasma touches the walls of the reactor its temperature falls and fusion stops.
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