Radioactivity Flashcards
Describe the structure of an atom.
- Atoms consist of a nucleus containing protons and neutrons.
- Electrons orbit the nucleus in energy levels.
- Example: Carbon-14 is written as ₆¹⁴C, where:
- 6 is the proton number.
- 14 is the mass number.
Define atomic (proton) number, mass (nucleon) number, and isotope.
- Atomic number (Z): Number of protons in the nucleus.
- Mass number (A): Total number of protons + neutrons.
- Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.
What are ionising radiations and how are they emitted?
- Alpha (α), beta (β⁻), and gamma (γ) radiation are emitted from unstable nuclei.
- The emission process is random.
- These radiations cause ionisation by knocking electrons from atoms.
Describe the nature of alpha, beta, and gamma radiation.
- Alpha (α): Helium nucleus (2 protons, 2 neutrons), highly ionising, stopped by paper.
- Beta (β⁻): High-energy electron, moderately ionising, stopped by aluminium.
- Gamma (γ): Electromagnetic wave, weakly ionising but highly penetrating, stopped by thick lead or concrete.
How do alpha, beta, gamma, and neutron radiation affect atomic and mass numbers?
- Alpha emission: Mass number decreases by 4, atomic number decreases by 2.
- Beta emission: A neutron changes into a proton, so atomic number increases by 1, mass number stays the same.
- Gamma emission: No change in atomic or mass numbers.
- Neutron emission: Mass number decreases by 1, atomic number stays the same.
How can ionising radiation be detected?
- Photographic film (darkens when exposed to radiation).
- Geiger-Müller detector (clicks when radiation is detected).
What are the sources of background radiation?
- Natural sources: Cosmic rays, rocks (radon gas), soil.
- Man-made sources: Nuclear power stations, medical uses (X-rays, radiotherapy).
- Background radiation levels vary by location.
What is half-life?
- The time taken for half of the radioactive nuclei in a sample to decay.
- It is different for different radioactive isotopes.
- Used in dating fossils and measuring the age of objects.
What is the equation for half-life calculations?
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Formula: N = N₀ × (1/2)^(t/T)
- N₀ = Initial activity or count rate.
- t = Time elapsed.
- T = Half-life of the isotope.
- Example: If a sample starts at 800 Bq and falls to 200 Bq in 6 hours, the half-life is 3 hours.
What are the uses of radioactivity in industry and medicine?
- Medical: Sterilising surgical equipment, treating cancer (radiotherapy), and medical tracers.
- Industrial: Checking welds for cracks (gamma scans), thickness control in paper mills.
- Carbon dating: Determining the age of organic materials.
- Smoke alarms: Alpha particles ionise air to detect smoke.
What is the difference between contamination and irradiation?
- Contamination: Radioactive material enters an object (e.g., dust, liquid spills).
- Irradiation: Exposure to radiation without direct contact.
- Irradiation stops when the source is removed, but contamination remains harmful.
What are the dangers of ionising radiation?
- Can cause mutations in living organisms, leading to cancer.
- Can damage cells and tissues.
- High doses cause radiation sickness.
- Radioactive waste needs safe disposal to reduce risks.
How can the risks of radioactive waste be reduced?
- Store waste in lead-lined containers.
- Bury waste deep underground or in geological storage sites.
- Use short half-life isotopes where possible.
How can the penetration power of radiation be investigated?
Equipment:
- Radioactive sources (α, β, γ)
- Geiger-Müller tube with counter
- Absorbing materials: Paper, aluminium, lead
- Ruler to measure distances
- Stopwatch for timed readings
Method:
1. Measure background radiation and subtract it from all readings.
2. Place a radioactive source at a fixed distance from the Geiger-Müller tube.
3. Record the count rate (clicks per second) without any material.
4. Insert paper between the source and detector, record the count rate.
5. Repeat with aluminium and lead, noting reductions in count rate.
Results:
- Alpha (α): Blocked by paper.
- Beta (β⁻): Blocked by aluminium.
- Gamma (γ): Reduced by lead but not fully blocked.
Conclusion:
- Radiation penetration ability increases in the order: Alpha < Beta < Gamma.
- Provides experimental proof of ionising radiation properties.
