Atomic and Nuclear r

Atomic and Nuclear r - 1. No specific comment available. 2....

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1. No specific comment available. 2. No specific comment available. 3. No specific comment available. 4. SL only This question was removed from the Paper. The syllabus guide refers to a graph of average binding energy per nucleon plotted against atomic number but all textbooks show graphs with mass number on the horizontal axis. Teachers are encouraged to teach the standard version of this graph, namely binding energy per nucleon as a function of mass number. 5. No specific comment available. 6. SL only Very rarely was it appreciated that changes in temperature and pressure do not affect rate of decay. Most candidates were able to complete the equation. The calculation was not often correct, as few candidates calculated the mass defect first. As a result, they got into difficulties with the complexities of the equation, and an inability to use index notation. This simple momentum problem was made complex for a significant number of candidates by putting it in the context of a nuclear decay. Candidates appear to learn their physics in ‘compartments’. Few succeeded in obtaining the ratio in (ii), and even fewer completed the deduction in part related to the kinetic energies in part (iii). The concept of fusion was generally well understood. However, the conditions required for it to occur, in terms of overcoming proton repulsion, was not well understood. 7. SL only The first two parts of the question were generally answered well but a great many candidates had a fundamental misunderstanding of the role of the moderator, thinking that along with the control rods, its purpose is to prevent an uncontrolled chain reaction. The idea that neutrons have more chance of producing fission with the scarce 235 U if they are slower moving, would seem to be not known to them. 1
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8. HL only Very rarely was it appreciated that changes in temperature and pressure do not affect rate of decay. Approximately 50% of candidates could relate decay constant to a probability of decay. However, many seemed to be unsure as to what would decay and in what length of time. The calculation was usually correct, but some candidates did not calculate the mass defect first. As a result, they got into difficulties with the complexities of the equation and an inability to use index notation. This simple momentum problem was explained satisfactorily by the more able candidates. Weaker candidates appear to learn their physics in ‘compartments’ and consequently were unable to give an explanation despite being told to consider momentum. Most succeeded in obtaining the ratio in (ii) even when their earlier explanations were unsatisfactory. The calculations based on radioactive decay proved to be accessible to most candidates although a significant number did not understand how to determine the average activity of the sample. The concept of fusion was generally well understood. However, the conditions required for it to
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This note was uploaded on 09/21/2009 for the course PHYSICS 2211 taught by Professor Uzer during the Fall '08 term at Georgia Tech.

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Atomic and Nuclear r - 1. No specific comment available. 2....

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