VCE Physics Unit 1:AOS 2 FINAL

Geiger counter function

Detects radioactive emissions by ionising argon gas inside a tube, creating a pulse of electrons that registers as a count.

Penetration power of radiation

Alpha: Low, stopped by paper | Beta: Moderate, stopped by a few mm of aluminium | Gamma: High, requires thick lead or concrete.

Ionising ability comparison

Alpha: Strongly ionising, interacts with many atoms | Beta: Moderately ionising, glancing collisions | Gamma: Weakly ionising, interacts infrequently.

Isotopes

Atoms with the same number of protons but different numbers of neutrons.

Radioisotope

An unstable isotope that emits radiation to become more stable.

Artificial transmutation

When a nucleus is altered by external particles, e.g., bombarding nitrogen with alpha particles to produce oxygen and hydrogen.

Strong nuclear force

Overcomes electrostatic repulsion between protons to hold the nucleus together.

Alpha decay

Nucleus emits an alpha particle (2 protons, 2 neutrons), reducing atomic number by 2 and mass number by 4.

Beta-minus decay

A neutron transforms into a proton, emitting a beta-minus particle (electron) and an antineutrino.

Beta-plus decay

A proton transforms into a neutron, emitting a beta-plus particle (positron) and a neutrino.

Gamma decay

The nucleus releases excess energy as gamma radiation after alpha or beta decay.

Decay series

A sequence of radioactive decays where an unstable isotope forms another unstable isotope until a stable isotope is reached.

Half-life

The time required for half of a radioactive sample to decay.

Nuclear fission

The splitting of a heavy nucleus into smaller nuclei, releasing energy.

Nuclear fusion

The combination of light nuclei to form a heavier nucleus, releasing energy.

Why fusion is harder to achieve

Requires overcoming strong electrostatic repulsion between positively charged nuclei.

E=mc^2 significance

Mass lost in nuclear reactions is converted into energy.

Binding energy per nucleon

Indicates nuclear stability; elements with highest binding energy per nucleon (around Fe-56) are the most stable.

Binding energy curve trends

Nuclei with A ≈ 60 are most stable | Lighter nuclei undergo fusion | Heavier nuclei undergo fission | Peak at Fe-56.

Mass defect

Difference between the mass of a nucleus and the sum of its nucleons' masses, due to energy binding them together.

Mass defect and nuclear energy

Missing mass is converted into energy (E=mc²), explaining energy release in fission and fusion.

Absorbed dose

Amount of radiation energy absorbed per kg of tissue, measured in Gray (Gy).

Equivalent dose

Considers the type of radiation and its biological impact, measured in Sieverts (Sv).

Effective dose

Accounts for the sensitivity of different organs to radiation.

Somatic vs Genetic effects of radiation

Somatic: Damage to body cells, leading to sickness or cancer | Genetic: Damage to reproductive cells, causing mutations in offspring.

Background radiation in Australia

~2.0 mSv annually from natural sources like cosmic rays and radon gas.

Becquerel (Bq)

Unit of radioactive activity; 1 Bq = 1 decay per second.

Why fusion releases more energy per nucleon

Fusion occurs in nuclei with low mass numbers, leading to a larger mass defect and higher energy release per nucleon.

Neutron-to-proton (N/Z) ratio and stability

If N/Z is too high → beta-minus decay | If N/Z is too low → beta-plus decay or alpha decay.

Why does a nucleus release gamma radiation?

After alpha or beta decay, the nucleus is in an excited state and releases extra energy as gamma rays to reach a stable state.

Why is ionisation dangerous to living tissue?

Ionisation can break molecular bonds in DNA, leading to mutations, cancer, or cell death.

Why is nuclear fusion difficult on Earth?

High temperatures and pressures are needed to overcome repulsion between positively charged nuclei.

How does half-life affect radioactive waste management?

Short half-life → decays quickly, but high initial activity | Long half-life → low activity but persists for a long time.

Why do we use lead shielding for gamma radiation?

Gamma rays are highly penetrating, and lead has a high density that absorbs their energy.

What is the weak nuclear force responsible for in the nucleus?

The weak nuclear force causes beta decay by changing a neutron into a proton (β⁻ decay) or a proton into a neutron (β⁺ decay).

What is the effect of shape and mass on nuclear criticality?

A larger mass and a compact shape increase the likelihood of a sustained fission chain reaction by keeping neutrons within the material.

How does neutron moderation work in a fission reaction?

Neutron moderators (like water or graphite) slow down fast neutrons, increasing the probability of further fission reactions.

How do α, β, and γ radiation affect humans?

α radiation: Highly ionising but stopped by skin; dangerous if ingested or inhaled. β radiation: Can penetrate skin but stopped by aluminium; causes moderate damage. γ radiation: Deeply penetrating; can cause DNA damage and increase cancer risk.

What are the differences between absorbed dose, equivalent dose, and effective dose?

Absorbed dose (gray, Gy): Energy absorbed per kg of tissue. Equivalent dose (sievert, Sv): Adjusts for radiation type's biological effect. Effective dose (sievert, Sv): Accounts for tissue sensitivity to radiation.

How are medical radioisotopes used in therapy?

They target cancer cells with radiation (e.g., iodine-131 for thyroid cancer), but can also harm healthy tissues if not carefully applied.

What is nuclear energy?

Nuclear energy is released when mass is converted into energy, according to Einstein's equation \( E = mc^2 \).

What does a binding energy curve show?

It shows that fusion (small nuclei joining) and fission (large nuclei splitting) both release energy because they move towards a more stable binding energy per nucleon.

Why is nuclear fusion not currently a viable energy source?

It requires extremely high temperatures and pressures, making it difficult to sustain in a controlled environment.

What are the advantages and disadvantages of nuclear energy for Australia?

Pros: Low carbon emissions, high energy output, reliable. Cons: Expensive infrastructure, radioactive waste, political/public opposition.