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Yr 10 Radioactivity (1) Learning Objectives
Students should understand the following:
- The basic structure of an atom is a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.
- Most of the mass of an atom is concentrated in the nucleus.
- The electrons are arranged at different distances from the nucleus (different energy levels).
- In an atom the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
- All atoms of a particular element have the same number of protons. The number of protons in an atom of an element is called its atomic number. The total number of protons and neutrons in an atom is called its mass number.
- Atoms can be represented as shown in this example:
- Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
- Atoms turn into positive ions if they lose one or more outer electron(s).
- Students should be able to relate differences between isotopes to differences in conventional representations of their identities, charges and masses.
- Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay.
- Activity is the rate at which a source of unstable nuclei decays.
- Activity is measured in becquerel (Bq)
- Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube).
- The nuclear radiation emitted may be:
- an alpha particle (α) – this consists of two neutrons and two protons, it is the same as a helium nucleus
- beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton
- a gamma ray (γ) – electromagnetic radiation from the nucleus
- a neutron (n).
- Required knowledge of the properties of alpha particles, beta particles and gamma rays is limited to their penetration through materials, their range in air and ionising power.
- Students should be able to apply their knowledge to the uses of radiation and evaluate the best sources of radiation to use in a given situation.
- Radioactive decay is random.
- The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
- Students should be able to explain the concept of half-life and how it is related to the random nature of radioactive decay.
- Students should be able to determine the half-life of a radioactive isotope from given information.
- Students should be able to calculate the net decline, expressed as a ratio, in a radioactive emission after a given number of half-lives.
- Radioactive isotopes have a very wide range of half-life values.
- Students should be able to explain why the hazards associated with radioactive material differ according to the half-life involved.
- Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.
- The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard.
- Irradiation is the process of exposing an object to nuclear radiation. The irradiated object does not become radioactive.
- Students should be able to compare the hazards associated with contamination and irradiation.
- Suitable precautions must be taken to protect against any hazard that the radioactive source used in the process of irradiation may present.
- Students should understand that it is important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists so that the findings can be checked by peer review.
- Nuclear radiations are used in medicine for the:
- exploration of internal organs
- control or destruction of unwanted tissue.
- Students should be able to:
- describe and evaluate the uses of nuclear radiations for exploration of internal organs, and for control or destruction of unwanted tissue
- evaluate the perceived risks of using nuclear radiations in relation to given data and consequences.
- LOGON SCIENCE CODES:
22.214.171.124, 126.96.36.199, 188.8.131.52, 184.108.40.206, 220.127.116.11, 18.104.22.168
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