Atoms, nuclei and radiation
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What did the α-particle scattering experiment reveal about the atom's structure?
The experiment showed that the atom contains a tiny, dense, positively charged nucleus. This refuted the plum pudding model and suggested most of the atom is empty space.
Describe the simple nuclear model of the atom.
The nuclear model consists of a central nucleus containing protons and neutrons, surrounded by orbiting electrons. The nucleus contains almost all the mass of the atom.
Distinguish between nucleon number (A) and proton number (Z).
Nucleon number (A) is the total number of protons and neutrons in the nucleus. Proton number (Z) is the number of protons in the nucleus, which defines the element.
What are isotopes?
Isotopes are forms of the same element that have the same number of protons but different numbers of neutrons in their nuclei.
Explain the notation A Z X for representing nuclides.
A Z X represents a nuclide where X is the element symbol, A is the nucleon number (mass number), and Z is the proton number (atomic number).
State the conservation laws applicable to nuclear processes.
In nuclear processes, both nucleon number (A) and charge (Z) are conserved. The total number of nucleons and the total charge before and after the process remain constant.
Describe the composition, mass, and charge of α-radiation.
α-radiation consists of helium nuclei (2 protons and 2 neutrons). It has a mass of approximately 4u and a charge of +2e (where e is the elementary charge).
Describe the composition, mass, and charge of β-radiation.
β-radiation consists of either electrons (β⁻) or positrons (β⁺). Both have a mass close to 0u and charges of -e (β⁻) or +e (β⁺), respectively.
Describe the composition, mass, and charge of γ-radiation.
γ-radiation consists of high-energy photons. It has zero mass and zero charge.
What is an antiparticle, and what is the antiparticle of an electron?
An antiparticle has the same mass as its corresponding particle but opposite charge. The antiparticle of an electron is a positron.
What particles are emitted during β⁻ and β⁺ decay?
During β⁻ decay, an electron and an antineutrino are emitted. During β⁺ decay, a positron and a neutrino are emitted.
Explain why α-particles have discrete energies, while β-particles have a continuous range of energies.
α-particles have discrete energies because the energy released in α-decay is fixed. β-particles have a continuous range of energies because the energy is shared with the (anti)neutrino also emitted in β-decay.
Represent the alpha decay of Uranium-238.
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Define the unified atomic mass unit (u).
The unified atomic mass unit (u) is defined as 1/12 of the mass of a neutral carbon-12 atom. It is approximately equal to 1.66 x 10⁻²⁷ kg.
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