Alpha, beta, gamma and neutron emission, their penetrating and ionising power, and balancing nuclear equations for each type of decay.
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1.What does radioactive decay mean?
An unstable nucleus gives out radiation as it changes to become more stable.
2.Is radioactive decay predictable?
No. It is a random process, so you cannot say when any particular nucleus will decay.
3.What is activity?
The rate at which a source of unstable nuclei decays.
4.What is the unit of activity?
The becquerel, Bq, which is one decay per second.
5.What is count rate?
The number of decays detected per second by a detector such as a Geiger-Muller tube.
6.What is an alpha particle?
Two neutrons and two protons, the same as a helium nucleus.
7.What is a beta particle?
A high speed electron ejected from the nucleus as a neutron turns into a proton.
8.What is gamma radiation?
Electromagnetic radiation emitted from the nucleus.
9.What can stop alpha radiation?
A sheet of paper, or a few centimetres of air.
10.What can stop beta radiation?
A few millimetres of aluminium.
11.What reduces gamma radiation?
Thick lead or several metres of concrete. It is never stopped completely, only reduced.
12.Rank the three types by penetrating power.
Gamma is most penetrating, then beta, then alpha which is least.
13.Rank the three types by ionising power.
Alpha is most ionising, then beta, then gamma which is least.
14.Why is alpha the most ionising?
It is a large, highly charged particle, so it interacts strongly with atoms it passes and knocks electrons off easily.
15.Why does high ionising power mean low penetration?
The radiation loses its energy quickly as it ionises atoms, so it cannot travel far through a material.
16.What happens to the mass number in alpha decay?
It decreases by 4.
17.What happens to the atomic number in alpha decay?
It decreases by 2.
18.What happens to the mass number in beta decay?
It stays the same.
19.What happens to the atomic number in beta decay?
It increases by 1.
20.Why does the atomic number increase in beta decay?
A neutron in the nucleus changes into a proton and an electron, and the electron is emitted.
21.What effect does gamma emission have on mass and atomic number?
Neither changes. Gamma emission only removes energy from the nucleus.
22.What happens when a nucleus emits a neutron?
The mass number decreases by 1 and the atomic number stays the same.
23.Uranium-238 emits an alpha particle. What are the new mass and atomic numbers?
Mass number 234 and atomic number 90.
24.Carbon-14 emits a beta particle. What are the new mass and atomic numbers?
Mass number stays 14 and atomic number becomes 7.
25.How do you check a nuclear equation is balanced?
The mass numbers must total the same on both sides, and so must the atomic numbers.
26.Which type of decay changes the element?
Alpha and beta both do, because the number of protons changes. Gamma does not.
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