Supervised assessment: Ionising radiation

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1 Physics 27 Sample assessment instrument and indicative Supervised assessment: Ionising radiation This sample is intended to inform the design of assessment instruments in the senior phase of learning. It highlights the qualities of student work and the match to the syllabus standards. Criteria assessed Knowledge and conceptual understanding Investigative processes Evaluating and concluding Assessment instrument The presented in this sample is in to assessment items. Context The instrument is a supervised assessment on the topic of ionising radiation and nuclear reactions. The focus of the unit was nuclear medicine and radioisotopes. Materials supplied Periodic table Constants: Speed of light = 3 x 8 m/s Mass of amu = kg ev =.6-9 J As stimulus material, Radioisotopes: their role in society today (a PowerPoint presentation produced by the Australian Nuclear Science and Technology Organisation (ANSTO) will be provided to students one week before the supervised assessment. Students may highlight the materials, but may not make any additional notations. Note: The instrument is not provided in this section as the items and s are presented together in the section of this document.

Instrument-specific criteria and standards Student s have been matched to instrument-specific criteria and standards; those which best describe the student work in this sample are shown below.

2 Instrument-specific criteria and standards Student s have been matched to instrument-specific criteria and standards; those which best describe the student work in this sample are shown below. For more information about the syllabus dimensions and standards descriptors, see Standard A Standard B Standard C Knowledge and conceptual understanding reproduction and interpretation of complex and challenging concepts, theories and principles (Q6) comparison and explanation of complex concepts, processes and phenomena (Q5) linking and algorithms, concepts, principles, theories and schema to find solutions in complex and challenging situations (Q7). reproduction and interpretation of challenging concepts, theories and principles (Q4, ) comparison and explanation of concepts, processes and phenomena (Q9, 4) linking and algorithms, concepts, principles, theories and schema to find solutions in challenging situations (Q3,, 6). reproduction of concepts, theories and principles (Q) explanation of simple processes and phenomena (Q3) algorithms, principles, theories and schema to find solutions in simple situations (Q2, 5). Investigative processes adaptation of equipment, and appropriate technology to gather, record and process valid data (Q6) systematic analysis of secondary data to identify relationships between patterns and trends (Q6). selection of equipment, and appropriate technology to gather, record and process data analysis of secondary data to identify patterns and trends (Q8). selection of equipment, and appropriate technology to gather and record data analysis of secondary data to identify obvious patterns and trends (Q8). Evaluating and concluding analysis and evaluation of complex scientific interrelationships (Q8) exploration of scenarios and possible outcomes with justification of conclusions (Q6, 8). analysis of complex scientific interrelationships explanation of scenarios and possible outcomes with discussion of conclusions (Q8). description of scientific interrelationships (Q2) description of scenarios and possible outcomes with statements of conclusion. Note: Colour highlights emphasise the qualities that discriminate between the standards. Key: Cognition demonstrated Qualifier Note: While the indicative demonstrates an on-balance match with the Standard A in each criterion, the instrument also provides opportunities for s across a range of syllabus standards descriptors. In order to show the relationship between the questions provided in the sample assessment instruments and the standards descriptors being addressed, the number of the item (or question, e.g. Q8) is provided in the matrix next to the descriptor. 2 Physics 27 Sample student assessment and s

3 Indicative Standard A The annotations show the match to the instrument-specific standards. Comments Question reproduction of concepts 25 52Te This symbol describes a particular nucleotide. Explain what each component of the symbol represents and state the number of subatomic particles in the element. Te is the symbol for the element tellurium. 25 is the mass number, which is the number of protons plus neutrons. 52 is the atomic number, which is the number of protons. Therefore, tellurium-25 has 73 neutrons, 52 protons and 52 electrons. Question 2 algorithms and theories to find solutions in simple situations Identify the isotope produced when particle. The daughter isotope is thallium Bi decays by emitting an alpha Bi 8Tl + 2He Question 3 Identify the second element formed in this reaction. If this daughter nucleus has mass number of 36, calculate how many neutrons are produced in the reaction n + U Sr +? +? n linking and concepts, principles, theories and schema to find solutions in a challenging situation = = n + U Sr + Xe + 2 n 92 Daughter nucleus is xenon neutrons are produced Queensland Studies Authority September 23 3

reproduction and interpretation of challenging concepts Question 4 (a) Compare Rutherford and Bohr models of the atom. (b) Identify the main evidence that caused acceptance of the Bohr model.

Electrostatic forces provided the attraction instead of gravity. The Bohr model proposed that electrons in atoms orbit at discrete sets of distances from the nucleus.

4 reproduction and interpretation of challenging concepts Question 4 (a) Compare Rutherford and Bohr models of the atom. (b) Identify the main evidence that caused acceptance of the Bohr model. (a) Rutherford s model of the atom had a small positive nucleus with empty space and electrons orbiting the nucleus like planets around the sun. Electrostatic forces provided the attraction instead of gravity. The Bohr model proposed that electrons in atoms orbit at discrete sets of distances from the nucleus. Both models suggested a central positive core with negative electrons around it of relatively the same size. The Bohr model was an improvement on the Rutherford model in that it had the electrons travelling at discrete levels from the nucleus. Rutherford model Bohr model (b) The Bohr model explained the Rydberg formula for the spectral emission lines of atomic hydrogen. The lines represented the energy released when an electron dropped back from an outer orbital to one nearer the nucleus. The Rutherford model was flawed in that spinning electrons would lose energy and spiral into the nucleus. It predicted all atoms were unstable. algorithms and theories to find solutions in simple situations. Question 5 A half-life of radium-226 is 62 years. What is the time taken in years for 7/8 of the material to decay? Assume original mass is kg. Every 62 y, half the material decays: kg 62 y kg 62 y 2 kg 62 y 4 8 kg It takes 3 62 y = 486 y for 7/8 of the material to decay. 4 Physics 27 Sample student assessment and s

5 Question 6 A student measured the count rate for a radioactive sample. The results are recorded in the following table. Time (minutes) Count rate (s - ) Ln (count rate) Using your graphics calculator, construct an appropriate graph of this data to determine the half-life of this sample. Include a sketch of your data plot in your. Time (minutes) Count rate (s - ) Ln (count rate) linking and concepts, principles, theories and schema to find solutions in a challenging situation Sketch adaptation of equipment, and appropriate technology to gather, record and process valid data. ln (count rate) Time (min) Queensland Studies Authority September 23 5

6 systematic analysis of secondary data to identify relationships between patterns and trends linking and concepts, principles, theories and schema to find solutions in a challenging situation exploration of scenarios and possible outcomes with justification of conclusions Question 6 (continued) Equation of line: y =.926x + 6. ln A =.926t + 6. A = e.926t+6. = e.926t e 6. = 43e.926t This equation is plausible since the initial count rate of 4 min - 43 min - from the equation. t /2 = ln2.926 = 7.5 The half-life of the sample is 7.5 minutes. This is plausible since the count rate drops from 4 s - to 94 s - in 8 minutes. Question 7 In the carbon cycle in the sun, firstly, carbon-2 (C-2) absorbs a proton to form a nucleus, X. Then X decays by positron emission to X 2, which then absorbs a proton to become X 3, which itself absorbs a proton to become X 4. X 4 then decays to X 5 by positron decay and X 5 absorbs a proton to give C-2 again. Determine the identities of X to X 5 and write a balanced equation for the net reaction. linking and concepts, principles, theories and schema to find solutions in a complex and challenging situation H He + 2e + + 2ν + 3γ 6 Physics 27 Sample student assessment and s

7 Question 8 The graph below shows changes in the composition of a kg sample of radioactive material over 5 years. The original parent material decays to produce a daughter material, which in turn decays to a stable material. 8 Mass (g) Time (y) Parent Daughter Stable material analysis of secondary data to identify obvious patterns and trends analysis of secondary data to identify patterns and trends explanation of scenarios and possible outcomes with discussion of conclusions (a) Estimate the half-life of the parent material. (b) Determine whether the half-life of the daughter material is longer or shorter than that of the parent material. Refer to features of the graph to explain your conclusion. (c) If the half-life of the daughter material was doubled, what would the differences in the material present be after 5 years? Show this by drawing lines to illustrate on the graph. (a) Half-life of parent material year (b) The half-life of the daughter material is longer than that of the parent material. This is evident because once the parent material has completely decayed (i.e. approx. 6 years), the rate of decrease of the daughter material is much slower than original rate of decrease of the parent material. (c) analysis and evaluation of complex scientific interrelationships exploration of scenarios and possible outcomes with justification of conclusions. If the half-life of the daughter material was doubled, it would take longer to decay. So there would be more of the daughter material remaining and less of the stable material produced at the 5-year mark. Queensland Studies Authority September 23 7

8 Question 9 comparison and explanation of concepts, processes and phenomena 238 U eventually decays to 26 Pb. During the decay there is α decay, β decay and γ radiation emitted. Compare the effect of α decay and β decay on the number of protons and neutrons in the nuclei and explain why Pb is the final element. α decay causes the number of protons and neutrons to diminish by two, whereas β decay diminishes the number of neutrons by one and increases the number of protons by one. The instability caused by α decay is corrected by the eventual β decay. Lead is more stable than the radioactive elements in the series before it. reproduction and interpretation of challenging concepts, theories and principles Question Uranium can be made to undergo fission by the bombardment of neutrons to form krypton-89 and barium-44. (a) Write the reaction to show all likely products of this reaction. (b) This artificial nuclear transformation is one of the nuclear reactions used to produce energy in nuclear power plants. Identify one characteristic of this reaction that makes it suitable for energy production and one danger associated with the reaction. (a) U + n 89 36Kr Ba + 3 n + γ (b) The reaction is suitable for energy production because the three neutrons that are produced can start a chain reaction. A danger is that the chain reaction must be kept in check so that the heat and radiation released can be controlled. linking and algorithms and concepts to find a solution in a challenging situation. Question One of the nuclear fusion reactions that occurs in stars is: Ne+ He Mg n where the masses are: 2 Ne = u, n =.8665u He = 4.263u, 24 2 Mg = u, Calculate the amount of energy (in MeV) released in this reaction. Mass deficit = (mass of neon + helium) (mass of Mg + neutron) = ( u u) ( u u) =.2745u =.2745u kg/u = kg E = mc 2 = kg (3 x 8 m/s) 2 = J = J.6-9 J/eV = ev = 2.56 MeV 8 Physics 27 Sample student assessment and s

9 description of scientific interrelationships In answering Questions 2 6, you may refer to information in the stimulus material Radioisotopes: their role in society today. Question 2 Consider the naturally occurring radioisotopes that are used in industry and science to measure the ages of different materials, i.e. carbon-4, chlorine-36, lead-2 and hydrogen-3. Describe the relationship between the half-life of each of these radioisotopes and the age of the materials they are able to measure. The longer the half-life of the radioisotope, the older the material it is able to measure. explanation of simple processes and phenomena Question 3 Explain why X-rays are useful in medical imaging. X-rays are able to penetrate soft tissue but not bone. An X-ray image shows the bones as a shadow. comparison and explanation of concepts, processes and phenomena Question 4 Explain the difference between diagnostic radiopharmaceuticals and therapeutic radiopharmaceuticals, giving an example of an isotope used in each process. Diagnostic radiopharmaceuticals are used to study the way the body is functioning and identify if something is going wrong. Isotopes that are used include Tc-99m and I-23. Therapeutic radiopharmaceuticals are used to kill cancer cells, which are sensitive to damage by radiation, e.g. I-3. comparison and explanation of complex concepts, processes and phenomena. Question 5 Technetium-99m is the most widely used radioisotope in nuclear medicine imaging. Compare the half-life of this isotope to other reactor-produced medical isotopes. Use this comparison to identify a reason why technetium- 99m may be a useful medical radioisotope. The half-life of Tc-99m is 6. hours. This is much shorter than the half-lives of other medical radioisotopes, e.g. Sm-53 (46.7 h), Mo-99 (66 h). This means Tc-99m will decay into stable isotopes quickly and will stop producing radiation after a day or two. This is an advantage because the patient will not be exposed to dangerous radiation for a long time. The other radioisotopes may be emitting radiation for weeks. Queensland Studies Authority September 23 9

10 reproduction and interpretation of complex and challenging concepts, theories and principles. Question 6 Americium-24 is used in smoke detectors. Given this function, identify what type of radiation americium-24 is likely to emit: alpha, beta or gamma particles. A smoke detector works because the Am-24 ionises atoms of air. To do this, it must produce radiation, which is highly ionising, i.e. alpha particles. If it produced beta or gamma radiation, this would probably pass through the air without ionising it. Am-24 emits alpha particles. Physics 27 Sample student assessment and s

Unit 3: Chemistry in Society Nuclear Chemistry Summary Notes

St Ninian s High School Chemistry Department National 5 Chemistry Unit 3: Chemistry in Society Nuclear Chemistry Summary Notes Name Learning Outcomes After completing this topic you should be able to :