1. By the end of this presentation, you should be able to: Select and use Coulomb’s law to determine the force of repulsion, and Newton’s law of gravitation to determine the force of attraction, between two protons at nuclear separations and hence the need for a short- range, attractive force between nucleons. Describe how the strong nuclear force between nucleons is attractive and very short-ranged. Use nuclear decay equations to represent simple nuclear reactions. State the quantities conserved in a nuclear decay. Estimate the density of nuclear matter.

2.  Consider a helium nucleus (which has two protons in it)  Calculate the force of repulsion between them ◦ Use Coulomb’s Law and r = 1.6 x 10 -15 m (two proton radii)

3.  Calculate the force of attraction due to their masses. You want to see if this force is sufficient to overcome the repulsion an keep the constituents of the nucleus from flying apart ◦ Use Newton’s Law of Gravitation and r=1.6 x 10 -5 m (two proton radii)

4.  The electrostatic repulsion >> the gravitational attraction.  F E / F G = 90 / 7.3 x 10 -35 = 10 36  There must be another force that is attractive, acts at this small separation, and is very strong

5. 1.It is the strongest of all four forces 2.It acts over a very short distance 3.If an attempt is made to push nucleons closer, the force will become repulsive 4.If you increase the separation, the force rapidly drops to zero. i.e. is has no influence outside of the nucleus

7.  Small nucleus  nuclear force acts over small distance  all nucleons affected and kept together  nucleus is stable: N = Z  Large nucleus  strong nuclear force cannot act to influence all nucleons  protons cannot be too close together or they will fly apart  more neutrons (than protons) will force the protons to be further apart  repulsive electrostatic force is smaller: N > Z  Nuclei with 83 protons experience such a large electrostatic repulsion that they are unstable. This results in radioactivity

8. ALPHA DECAY: The nucleus emits a particle which consists of 2 protons and 2 neutrons. Alpha decay of plutonium-240 into uranium-236 and an alpha particle

9. BETA DECAY: There are 2 types of beta decay  beta-plus ( b + ) decay eta–minus ( b - ) decay tthe “weak interaction” between “quarks” is responsible for beta decay Beta-minus decay: a neutron in the nucleus decays into a proton (stays in the nucleus) and an electron and an electron antineutrino. The electron is detected as the beta particle. Beta-plus decay: a proton in the nucleus decays into a neutron (stays in the nucleus) and an electron and an electron neutrino. The electron is detected as the beta particle.

10. 1. Calculate the density of a proton considering: 2. Neutrons have a similar mass and volume to protons, therefore a similar density. 3. Since nuclei are made up of protons and neutrons in close proximity, then this must be similar to the density of the any nucleus.