12. Nuclear Physics

Geiger-Marsden \mathbf{\alpha}α-scattering

Experiment: a beam of \alphaα-particles is fired at thin gold foil
Results of the experiment:
- Most particles pass straight through
- Some are scattered appreciably
- Very few – 1 in 8,000 – suffered deflections > 90^o
Conclusion:
- All mass and charge concentrated in the center of atom \therefore∴ nucleus is small and very dense
- Nucleus is positively charged as \alphaα-particles are repelled/deflected

The Nuclear Atom

Nucleon number: total number of protons and neutrons
Proton/atomic number: total number of protons
Isotope: atoms of the same element with a different number of neutrons but the same number of protons

During a nuclear process, nucleon number, proton number and mass-energy are conserved.

	α-particle	β-particle		γ-ray
	α-particle	β⁻	β⁺
Identity	Helium nucleus	Fast-moving electron/positron		Electro- magnetic
Symbol	₂⁴He	_− 1⁰e	_+ 1⁰e	γ
Charge	+ 2	− 1	+ 1	0
Relative Mass	4	1/1840		0
Speed	Slow (10⁶ ms^-1)	Fast (10⁸ ms^-1)		V of Light (3 × 10⁸ ms^-1)
Energy	Discrete	Varying
Stopped by	Paper	Few mm of aluminum		Few cm of lead
Ionizing power	High	Low		Very Low
Effect of Magnetic	Deflected slightly	Deflected greater		Undeflected
Effect of Electric	Attracted to -ve	Attracted to
Effect of Electric	Attracted to -ve	+ve	-ve

\mathbf{\alpha}α - decay: loses a helium proton
\mathbf{\beta}^{\mathbf{-}}β^-- decay: neutron turns into a proton and an electron & electron antineutrino are emitted
\mathbf{\beta}^{\mathbf{+}}β⁺- decay: proton turns into a neutron and a positron & electron neutrino are emitted
\mathbf{\gamma}γ - decay: a nucleus changes from a higher energy state to a lower energy state through the emission of electromagnetic radiation (photons)

Fundamental Particle: a particle that cannot be split up into anything smaller.
Electron is a fundamental particle but protons and neutrons are not.
Protons and neutrons are made up of different combinations of smaller particles called quarks.
Table of Quarks:
Quark Models:
- All particles have their corresponding antiparticle.
- A particle and its antiparticle are essentially the same except for their charge.
- Table of Antiquarks:These antiquarks combine to similarly form respective antiprotons and antineutrons

There are other families under Leptons
Leptons are a part of elementary particles
- There are other families under Hadrons too
- Hadrons are a part of composite particles