radioactivity Flashcards
State what is meant by radioactive decay.
when unstable nuclei become more stable by emitting particles (known as nuclear radiation)
Describe the main features of a plum pudding model.
→ positively charged sphere
→ with -ive charges spread throughout
→ mass is evenly distributed
Describe the experimental set up for the alpha scattering experiment.
→ narrow beam of alpha particle
→ directed at thin piece of gold foil
→ microscope with fluorescent screen as detector
→ all in a vacuum
Describe the three results observed during Rutherford’s alpha scattering experiment.
→ most particles passed straight through = atom was mostly empty space
→ some were deflected by large angles = +ive charge was concentrated
→ some particles bounced back = most of atom’s mass is concentrated
Describe the nuclear model of the atom.
→ +ive nucleus where mass is concentrated
→ surrounded by -ve charges
Explain in terms of binding energy, why energy can be released when two nuclei undergo nuclear fission.
→ total mass of nuclei is more than mass of fusion
product
→ binding energy per nucleon increases when a nucleus is formed by fusion
State what is meant by corrected count rate.
measure and deduct background count (rate)
State two sources of radiation that has contributed to exposure of background radiation.
→ / nuclear waste
→ x-rays
Explain what is meant by a thermal neutron.
→ low (kinetic) energy neutrons
→ in thermal equilibrium with the moderator /
decsy constanr
probability of decay per unit time/
Explain how a thermal nuclear reactor works.
- U-235 undergoes nuclear fission
- releases heat energy and heats coolant
- coolant heats water and turns it into steam
In a nuclear reactors, state the purpose of a :
moderator
coolant
control rod
- slows down neutrons
- To remove the heat released by the fission reactions
- to absorb neutrons and maintain chain reaction
Explain why there is this imbalance between proton and neutron numbers by referring to
the forces that operate within the nucleus
→ strong nuclear force holds nucleons together
→ electromagnetic force acts on protons, increases with proton number
→ more neutrons are required to keep nuclei together as they reduce repulsion between protons
Explain why the metastable form of the isotope of technetium is suitable for use in medical diagnosis.
→ it only emits λ-rays
→ half-life is short enough not to remain in the body for too long but long enough for examination
Describe what happens when neutrons interact with U-235 and U-238 nuclei in a thermal
nuclear reactor.
→ thermal neutron with correct kinetic energy is absorbed by U-235
→ U-236 splits to produce daughter nuclei and more neutrons
→ these neutrons are scattered by U-238
