PHYSICS Radioactivity CHAPTER 7 (P5- The half-line of a radioactive…
PHYSICS Radioactivity CHAPTER 7
P1- A radioactive substance contains unstable nuclei that become stable by emitting radiation.
P2- An atoms has a small positively charged central nuclear where most of the atom's mass is located.
P4- Gamma radiation is stopped by thick lead and has an unlimited range in air. It consists of electromagnetic radiation.
P1- Radioactive sources emit alpha, beta and gamma radiation.
P1- There are three main types of radiation from radioactive substances - alpha, beta, gamma.
P1- Radioactive decay is a random event - you can't predict or influence when it will happen.
P2- Rutherford used alpha particles to probe inside atoms. He found that some of the alpha particles were scattered through large angels.
P2- The 'plumb pudding model' could not explain why some alpha particles were scattered through large angels.
P2- The nuclear model of the atom correctly explained why some alpha particles scattered through large angels.
P4- Alpha, beta and gamma radiation ionise substances they pass through. Ionisation in a living cell can damage or kill the cell.
P4- Beta radiation is stopped by a thin sheet of metal and has a range of about one metre in air.It consist of fast-moving electrons emitted from the nucleus. It is less ionising than alpha radiation and more ionising than gamma radiation.
P4- alpha radiation is stopped by paper and has a range of a few centimetres in air. It consists of particles, each composed of two protons and two neutrons. It has the greatest ionising power.
P5- The count rate of a Geiger counter caused by a radioactive source decreases as the activity of the source decreases.
P5- The half-line of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
P5- The count rate after n half-lives = the initial count rate ÷ 2n.
P5- The number of atoms of a radioactive isotope and the count rate both decrease by half every half-life.
P6- Radioactive isotopes are used in medicine for medical imaging, treatment of cancer, and as tracers to monitor organs.
P6- How useful a radioactive isotope is depends on; -its half life
-the type of radiation it gives out.
P6- For medical imaging with a radioactive isotope and for medical tracers, the half-life should be not too short and not too long.
P6- A gamma beam or a radioactive implant can destroy cancer cells in a tumour.
P7-Nuclear fission is the splitting of an atom's nucleus into two smaller nuclei and the release of two or three neutrons and energy.
P7- Induced fission occurs when a neutron is absorbed by a uranium-235 nucleus or a plutonium-239 nucleus and the nucleus splits. Spontaneous fission occurs without a neutron being absorbed.
P7- A chain reaction occurs in a nuclear reactor when each fission event causes further fission events.
P7- In a nuclear reactor, control rods absorb fission neutrons to ensure that, on average, only one neutron per fission goes on to produce further fission.
P8- Nuclear fusion is the process of forcing the nuclei of two atoms close enough together so that they form a single larger nucleus.
P8- Nuclear fusion can be brought about by making two light nuclei collide at very high speed.
P8- Energy is released when two light nuclei are fused together. Nuclear fusion in the suns core releases energy.
P8- A fusion reactor needs to be at a very high temperature before nuclear fusion can take place. The nuclei to be fused are difficult to contain.
ATOMS AND RADIATION
THE DISCOVERY OF THE NUCLEUS
CHANGES IN THE NUCLEUS
ALPHA, BETA AND GAMMA RADIATION
ACTIVITY AND HALF-LIFE
NUCELAR RADIATION IN MEDICINE