Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.
In the early nineteenth century, Dalton proposed some fundamental properties of atoms that would explain existing laws of chemistry. One century later, a range of experiments provided evidence that enabled scientists to develop models of the structure of the atom. These included using radiation in the form of X-rays and alpha particles, and the passing of particles through a magnetic field to determine their mass (ACSCH010). Evidence from French physicist Becquerel’s discovery of radioactivity suggested the presence of subatomic particles, and this was also a conclusion from gas discharge experiments. British physicist J.J. Thomson was able to detect electrons, and his results, combined with the later work of Millikan, an American experimental physicist, resulted in both the charge and mass of electrons being calculated (ACSCH009). The British chemist Rutherford proposed a model of the atom comprising a heavy nucleus surrounded by space in which electrons were found, and Danish physicist Bohr’s model further described how these electrons existed in distinct energy levels. The last of the main subatomic particles, the neutron, was discovered by the English physicist Chadwick in 1932, by bombarding samples of boron with alpha particles from radioactive polonium (ACSCH010).
Radioisotopes have a wide variety of uses, including Carbon-14 for carbon dating in geology and palaeobiology; radioactive tracers such as Iodine-131 in nuclear medicine; radioimmuno-assays for testing constituents of blood, serum, urine, hormones and antigens; and radiotherapy that destroys damaged cells (ACSCH011). Use of radioisotopes requires careful evaluation and monitoring because of the potential harmful effects to humans and/or the environment if their production, use and disposal are not managed effectively (ACSCH013). Risks include unwanted damage to cells in the body, especially during pregnancy, and ongoing radiation produced from radioactive sources with long half-lives.
Analysis of the distribution of elements in living things, Earth and the universe has informed a wide range of scientific understandings, including the role of calcium exclusion from bacteria in the evolution of shells and bones; the proliferation of carbon (rather than silicon, which has similar properties and is more abundant in Earth’s crust) in living things; the elemental composition of historical artefacts; and the origin of elements through nuclear fusion in stars (ACSCH011). Analysis of element distribution is informed by data from spectral analysis and other technologies. Evidence from these techniques enables scientists to draw conclusions about a range of phenomena, such as the chemical changes involved in natural processes in both biological and cosmological systems, and the geographic source of historical artefacts (ACSCH014).