3.2.1.2 Stable and Unstable Nuclei Flashcards
Name the two forces acting on the nucleons in the nucleus of the atom.
Electromagnetic Force
Gravitational Force
How does the electromagnetic force act on the nucleus?
The electromagnetic forces cause the positively charged protons to repel each other within the nucleus.
How does the gravitational force act in the nucleus?
The gravitational forces causes all the nucleons in the nucleus to attract to each other due to their mass.
Which if larger, the electromagnetic repulsion or the gravitational attraction?
The electromagnetic repulsion is much larger.
What would happen if these two forces were the only two acting in the nucleus?
The nucleons would fly apart.
What is the nuclear strong force?
This force is the attractive force which holds stable nuclei together, so that they do not disintegrate.
Is the nuclear strong force attractive or repulsive?
It is an attractive force.
Why does the Nuclear strong force have to be stronger than the electromagnetic forces?
It has to be stronger because it must overcome the repulsion between the protons in the nucleus, and keep all the nucleons together.
What is 1 femtometre equivalent to?
1 femtometre is equivalent to 10^-15 metres.
What is the range of the nuclear strong force?
It has a very short range.
No more than about 3 - 4 femtometres.
This is about the same as the diameter of a nucleus.
What does this fact about the range tell us about the force?
It tells us that the force can only hold nucleons together when they are separated by anything up to this range,
What is the range of the electrostatic force acting on two charged particles?
It has an infinite range.
How does the nuclear strong force act on nucleons?
It works equally between all nucleons. It has the same effect on two protons, as it does between two neutrons, or a proton and neutron.
This means that the size of the force is the same in all situations.
What fact tells relates the range of the force to the nature of the force?
The nuclear strong force is an attractive force from 3-4 femtometres, down to about 0.5 fm.
What is the nature of the nuclear strong force below 0.5 fm? Why?
It is a repulsive force that acts to prevent neutrons and protons being pushed into each other.
Describe the graph that shows the relationship between the nuclear strong force and nucleon separation.
Attraction and Repulsion on the x-axis.
Nucleon Separation on the y - axis.
Repulsive force upwards on the x axis (>0)
Attractive force downwards on the x axis (<0)
Nuclear Strong force:
Curve which starts repulsive, then cuts the x-axis and becomes attractive to a maximum, then becomes less and less attractive, and flattens.
Cuts the x axis at 0.5fm and starts to plateau at 3 fm.
Electromagnetic Force:
Repulsive force which extends over a larger range.
Remains repulsive.
At low nucleon separations, it is high, but as the y variable increases, it decreases.
Where on the graph is the equilibrium separation for the nuclear strong force?
Where the force curve crosses the x-axis at about 0.5 fm.
Why do unstable nuclei emit particles?
To become more stable.
What is it called when an unstable nucleus emits particles to become more stable?
It is called nuclear decay.
When does alpha decay happen?
Alpha decay only happens in very big atoms with more than 82 protons.
Why does alpha decay only happen in these kinds of atoms?
The nuclei of atoms like these are just too big for the nuclear strong force to keep them stable. To make them more stable, they must emit an alpha particle from their nucleus.
What is an alpha particle?
An alpha particle is the nucleus of a helium atom.
4He2.
An alpha particle has 2 protons and 2 neutrons.
What happens to the atom when an alpha particle is emitted?
The proton number decreases by two.
The nucleon number decreases by four.
What is the range of alpha particles?
They have a very short range - only a few centimetres in air.
What is beta-minus decay?
Beta-minus decay is the emission of a fast moving electron from a nucleus, and an antineutrino particle.
When does beta decay happen?
Beta decay happens in isotopes that are neutron rich. This means that they have too many neutrons compared to protons in their nucleus.
What are the properties of a beta-minus particle?
It has the same mass and charge of an electron.
What happens to a neutron when a nucleus ejects a beta minus particle?
One of the neutrons becomes a proton. The beta particle is created when the change happens and is emitted instantaneously. In addition, an antiparticle with no charge called an antineutrino is emitted.
What happens to the atomic and mass number when a beta particle is emitted?
The proton number increases by one, as a neutron changed into a proton. Therefore the element changes.
The nucleon number stays the same.
What is the purpose of the antineutrino particle?
It carries away some energy and momentum.
What is the range of a beta-particle?
Beta particles have a much greater range than alpha particles. They can travel up to several metres through air.
What is gamma radiation?
Gamma radiation is electromagnetic radiation by an unstable nucleus.
What are the properties of gamma radiation?
It can pass through thick metal plates.
It has no mass and no charge.
When is gamma radiation emitted?
It is emitted by a nucleus with too much energy, following an alpha or beta decay.
What happens to the atom when gamma radiation is emitted? Why?
The proton number and nucleon number does not change as gamma radiation is only energy and makes no difference to the isotope/ nucleus itself.
