measurement or must be administered in a dangerously large dose Nuclear

Measurement or must be administered in a dangerously

This preview shows page 17 - 19 out of 20 pages.

measurement or must be administered in a dangerously large dose Nuclear Stability Inside nucleus, nucleons are sufficiently close → pull of the strong nuclear force is much greater than repulsion between protons → stable nucleus The strong nuclear force requires ideal distances between the protons o If distance between protons is too small, then strong nuclear force is repulsive o If the average separation of protons is too large, then the strong nuclear force is too weak to hold them Thus, if there are too few neutrons, or too many neutrons, the nucleus becomes unstable Sample Question: Outline the role of neutrons in the stability of nuclei. The repulsion due to the electrostatic forces between protons in a larger nucleus makes the nucleus less stable so more neutrons are required to maintain stability Large nuclei require extra neutrons add extra space between the protons, thus, decreasing their repulsions Model and explain the process of nuclear fission including the concepts of controlled and uncontrolled chain reactions and account for the release of energy in the process Fermi’s Contribution 17
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FINAL HSC PHYSICS NOTES Fermi’s conclusion – 2.5 neutrons with enough energy to cause additional transmutations needed to be emitted (on average) each transmutation for a chain reaction to be initiated and continued o The speed of bombarding neutrons resulted in different products Purpose of experiment – use neutrons to bombard uranium to see if he could produce new elements o Neutrons → relatively massive and uncharged → penetrate more than charged particles of similar mass o Uranium → naturally radioactive and very unstable to begin with Observation – fission of uranium atoms produced more neutrons o If fission was initiated by a bombarding neutron, then the neutrons produced by the fission process could also be used to produce more fission, and more neutrons → chain reaction Sample Question: Distinguish between the processes of nuclear fission and transmutation Transmutation is when an atomic nucleus decays into that of another element and releases radiation Nuclear fission involves the splitting of ‘heavy’ nuclei to form two or more daughter nuclei with the release of up to several neutrons and a large amount of energy Sample Question: Explain the difference between an uncontrolled fission reaction and a controlled fission reaction. Uncontrolled fission occurs when the rate of fission is not controlled and a chain reaction occurs that accelerates rapidly, resulting in an explosion and the release of huge amounts of energy Controlled fission occurs when the rate of fission is achieved o Keeping fuel rods separated from one another so they are near the critical mass density o Using control rods that absorb neutrons to control the number of neutrons available in the reactor o Using a moderator (heavy water) that slows high energy neutrons down to the lower energies Analyse relationships that represent conservation of mass-energy in spontaneous and artificial nuclear transmutations, including alpha decay, beta decay, nuclear fission and nuclear fusion
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