1.2 Stable and Unstable Nuclei Flashcards
What are the forces acting on the nucleons in the nucleus?
The electromagnetic force
The gravitational force
The strong nuclear force
What does the electromagnetic force cause in the nucleus?
The positively charged protons in the nucleus to repel each other
What does the gravitational force cause in the nucleus?
All the nucleons in the nucleus to attract each other due to their mass
What would happen if the gravitational and electromagnetic forces were the only forces acting in the nucleus?
The nucleus would fly apart as the repulsion from the electromagnetic force is much larger than the gravitational attraction
How strong is the strong nuclear force?
To hold the nucleus together, the strong nuclear force must be an attractive force that’s stronger than the electromagnetic force
What is the range of the strong nuclear force?
- repulsive until 0.5fm
- becomes attractive after 0.5fm
- as separation increases past the maximum attractive value attraction falls rapidly towards zero after about 3fm
How does the strong nuclear force work between nucleons?
The strong nuclear force works equally between all nucleons, meaning the size of the force is the same whether its proton-proton, neutron-neutron or proton-neutron
What is the range of the electromagnetic force?
The electromagnetic repulsive force extends indefinitely
Which nucleons feel the electromagnetic force?
Protons
When does alpha decay happen?
Alpha decay happens in very large atoms (more than 82 protons) because the nuclei of these atoms are too large for the strong nuclear force to keep them together, so they emit an alpha particle to make themselves more stable
What happens in alpha decay?
- An alpha particle is emitted (2 neutrons, 2 protons)
- proton number decreases by 2
- nucleon number decreases by 4
What is the range of alpha particles?
Very short range - only a few cm in air
How would you measure the range of an alpha particle?
- observe the tracks left by alpha particles in a cloud chamber
- bring a Geiger counter or spark counter up close to an alpha source and then move it away slowly
What is beta minus decay?
The emission of an electron from the nucleus along with an antineutrino particle
When does beta minus decay happen?
Beta minus decay happens in isotopes that are neutron-rich (have too many neutrons compared to protons in their nucleus)
What happens in the nucleus in beta minus decay?
One of the neutrons in the nucleus is changed into a proton
What happens to proton and nucleon number in beta minus decay?
- proton number increases by 1
- nucleon number stays the same§
What happens to proton and nucleon number in beta minus decay?
- proton number increases by 1
- nucleon number stays the same
How is energy and momentum conserved in beta minus decay?
The antineutrino particle released carries away some energy and momentum
What is the range of beta particles in air?
They can travel up to several metres in air (much greater than alpha particles)
