When radioactive substances decay

Transcription

1 When radioactive substances decay P2 72 minutes 72 marks Page of 3

2 Q. (a) The names of three types of radiation are given in List A. Some properties of these three types of radiation are given in List B. Draw one line from each type of radiation in List A to its correct property in List B. List A Type of radiation alpha beta gamma List B Property of radiation will pass through paper but is stopped by thin metal has the shortest range in air will not harm human cells is very weakly ionising (3) (b) The radioactive isotope iodine-23 can be used by a doctor to examine the thyroid gland of a patient. The iodine, taken as a tablet, is absorbed by the thyroid gland. The gamma radiation emitted as the iodine atoms decay is detected outside the body. The doctor uses an isotope emitting gamma radiation to examine the thyroid gland rather than an isotope emitting alpha or beta radiation. Which one of the following gives a reason why gamma radiation is used? Tick ( ) one box. Gamma radiation will pass through the body. Gamma radiation is not deflected by a magnet. Gamma radiation has a long range in air. () Page 2 of 3

3 (c) Iodine-23 has a half-life of 3 hours. Use a word from the box to complete the sentence. all half most After 3 hours... of the iodine-23 atoms the thyroid absorbed have decayed. () (d) Iodine-23 and iodine-3 are two of the isotopes of iodine. Draw a ring around the correct answer to complete the sentence. electrons The nucleus of an iodine-23 atom has the same number of neutrons as the protons nucleus of an iodine-3 atom. () (Total 6 marks) Q2. (a) Sources of background radiation are either natural or man-made. Which two of the sources listed in the box are natural sources of background radiation? Draw a ring around each of your answers. cosmic rays nuclear accidents X-rays radon gas (2) Page 3 of 3

4 (b) A teacher used a Geiger-Műller (GM) tube and counter to measure the background radiation in her laboratory. The teacher reset the counter to zero, waited one minute and then took the count reading. The teacher repeated this two more times. The three readings taken by the teacher are given in the table. Count (i) The three readings are different. What is the most likely reason for this? Tick ( ) one box. The teacher did not reset the counter to zero. Radioactive decay is a random process. The temperature in the laboratory changed. () Calculate the mean (average) value of the three readings given in the table. Mean (average) value =... counts () Page 4 of 3

5 (iii) The diagram shows how the teacher used the GM tube and counter to measure the radiation emitted from a radioactive source. The counter was reset to zero. The count after one minute was 59. Calculate how many counts were due to the radiation from the radioactive source. Counts due to the radiation from the radioactive source =... () (iv) The teacher then put a powerful magnet between the radioactive source and the GM tube. The counter was reset to zero. The number on the counter shows the count after one minute. What type of radiation was being emitted from the radioactive source? Draw a ring around your answer. alpha beta gamma Explain the reason for your answer. (3) Page 5 of 3

6 (c) At the end of the lesson the teacher put the radioactive source back inside its storage box. Why is the inside of the box lined with lead? () (d) Which one of the following questions cannot be answered by scientific study? Tick ( ) one box. Where does background radiation come from? What is meant by the half-life of a radioactive source? Should radioactive waste be dumped in the oceans? () (Total 0 marks) Page 6 of 3

7 Q3. The pie chart shows the sources of the background radiation and the radiation doses that the average person in the UK is exposed to in one year. Radiation dose is measured in millisieverts (msv). (a) (i) What is the radiation dose that the average person in the UK receives from radon gas? Radiation dose from radon gas =... msv () A person may receive a higher than average dose of radiation from background sources. Suggest two reasons why (2) Page 7 of 3

8 (b) Exposure to radon gas can cause lung cancer. A recent study has compared the risk of getting lung cancer, by the age of 75 years, for cigarette smokers and non-smokers. The people in the study had been exposed throughout their lives to different levels of radon gas. A summary of the data produced from the study is given in the table. Exposure to radon gas Risk of lung cancer by age of 75 Non-smoker Smoker No exposure 0.4 % 0 % Moderate exposure Very high exposure.0 % 4 %.5 % 32 % (i) Why were people that have had no exposure to radon gas included in the study? () Using information from the table, what conclusions can be made about exposure to radon gas and the risk of getting lung cancer? (2) Page 8 of 3

9 (c) At the moment, the regulations designed to protect people from over-exposure to radiation are based on a model called the linear no-threshold (LNT) model. Some scientists believe that the LNT model is too simple.these scientists believe that at low radiation levels a process called radiation hormesis happens. The graphs show that each model suggests a link between the risk of developing a cancer and exposure to low levels of radiation. The link between the risk of developing cancer and exposure to low levels of radiation suggested by each of the models is different. Describe how (2) (d) Scientists have conducted experiments in which mice have been exposed to different levels of radiation. The number of mice developing a cancer has then been measured. Discuss whether it is ethical to use animals in scientific experiments (2) (Total 0 marks) Page 9 of 3

10 Q4. (a) The graph shows how the count rate from a sample containing the radioactive substance cobalt-60 changes with time. (i) What is the range of the count rate shown on the graph? From... counts per second to... counts per second. () How many years does it take for the count rate to fall from 200 counts per second to 00 counts per second? Time =... years () (iii) What is the half-life of cobalt-60? Half-life =... years () Page 0 of 3

11 (b) The gamma radiation emitted from a source of cobalt-60 can be used to kill the bacteria on fresh, cooked and frozen foods. Killing the bacteria reduces the risk of food poisoning. The diagram shows how a conveyor belt can be used to move food past a cobalt-60 source. (i) Which one of the following gives a way of increasing the amount of gamma radiation the food receives? Put a tick ( ) in the box next to your answer. Increase the temperature of the cobalt-60 source. Make the conveyor belt move more slowly. Move the cobalt-60 source away from the conveyor belt. () To protect people from the harmful effects of the gamma radiation, the cobalt-60 source has thick metal shielding. Which one of the following metals should be used? Draw a ring around your answer. aluminium copper lead () Page of 3

12 (c) A scientist has compared the vitamin content of food exposed to gamma radiation with food that has not been exposed. The table gives the data the scientist obtained when she tested kg of cooked chicken. Vitamin Food not exposed to gamma radiation Mass in milligrams Food exposed to gamma radiation Mass in milligrams B B E Niacin Riboflavin Considering only this data, which one of the following is a correct conclusion? Put a tick ( ) in the box next to your answer. Vitamin content is not affected by gamma radiation. Gamma radiation completely destroys some types of vitamin. Exposure increased the content of some types of vitamin. () (Total 6 marks) Q5. In 20 an earthquake caused severe damage to a nuclear power station in Japan. The damage led to the release of large amounts of radioactive iodine-3 atmosphere. into the (a) The table gives some information about an atom of iodine-3. Complete the table. mass number 3 number of protons 53 number of neutrons () Page 2 of 3

13 (b) Complete the sentence. The number of protons in an atom is called the proton number or the... number. () (c) An atom of iodine-3 decays into an atom of xenon (Xe) by emitting a beta particle. (i) The decay of iodine-3 can be represented by the equation below. Complete the equation by writing the correct number in each of the two boxes. (2) A sample of rainwater contaminated with iodine-3 gives a count rate of 200 counts per second. Calculate how many days it will take for the count rate from the sample of rainwater to fall to 75 counts per second. Half-life of iodine-3 = 8 days Show clearly how you work out your answer.... days (2) (iii) If people drink water contaminated with iodine-3, the iodine-3 builds up in the thyroid gland. This continues until the thyroid is saturated with iodine-3 and cannot absorb any more. The radiation emitted from the iodine-3 could cause cancer of the thyroid. In Japan, people likely to be drinking water contaminated with iodine-3 were advised to take tablets containing a non-radioactive isotope of iodine. Suggest why this advice was given. (2) (Total 8 marks) Page 3 of 3

14 Q6. (a) A teacher used a Geiger-Műller (GM) tube and counter to measure the background radiation in her laboratory. The teacher reset the counter to zero, waited one minute and then took the count reading. The teacher repeated the procedure two more times. (i) Background radiation can be either from natural sources or from man-made sources. Name one man-made source of background radiation. () The three readings taken by the teacher are given in the table. Count after one minute The readings given in the table are correct. Why are the readings different? () (b) Some scientists say they have found evidence to show that people living in areas of high natural background radiation are less likely to develop cancer than people living in similar areas with lower background radiation. The evidence these scientists found does not definitely mean that the level of background radiation determines whether a person will develop cancer. Suggest a reason why () Page 4 of 3

15 (c) An atom of the isotope radon-222 emits an alpha particle and decays into an atom of polonium. An alpha particle is the same as a helium nucleus. The symbol below represents an alpha particle. (i) How many protons and how many neutrons are there in an alpha particle? Number of protons =... Number of neutrons =... (2) The decay of radon-222 can be represented by the equation below. Complete the equation by writing the correct number in each of the two boxes. (2) (d) The graph shows how, in a sample of air, the number of radon-222 nuclei changes with time. Use the graph to find the half-life of radon-222. Time in days Show clearly on the graph how you obtain your answer. Half-life =... days (2) (Total 9 marks) Page 5 of 3

16 Q7. Atoms contain three types of particle. (a) Draw a ring around the correct answer to complete the sentence. The particles in the nucleus of the atom are electrons and neutrons. electrons and protons. neutrons and protons. () (b) Complete the table to show the relative charges of the atomic particles. Particle Relative charge Electron Neutron Proton (2) (c) (i) A neutral atom has no overall charge. Explain this in terms of its particles..... (2) Complete the sentence. An atom that loses an electron is called an... and has an overall... charge. (2) Page 6 of 3

17 (d) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Some substances are radioactive. They may emit alpha or beta particles. Describe the characteristics of alpha particles and beta particles in terms of their: structure penetration through air and other materials deflection in an electric field (6) (Total 3 marks) Page 7 of 3

18 Q8. Nuclear fission and nuclear fusion are two processes that release energy. (a) (i) Use the correct answer from the box to complete each sentence. Geiger counter nuclear reactor star Nuclear fission takes place within a.... Nuclear fusion takes place within a.... (2) State one way in which the process of nuclear fusion differs from the process of nuclear fission... () (b) The following nuclear equation represents the fission of uranium-235 (U-235). Chemical symbols: Ba - barium Kr - krypton (i) Use the information in the equation to describe the process of nuclear fission (4) Page 8 of 3

19 An isotope of barium is Ba-39. Ba-39 decays by beta decay to lanthanum-39 (La-39). Complete the nuclear equation that represents the decay of Ba-39 to La-39. (3) (Total 0 marks) Page 9 of 3

20 M. (a) 3 lines correct allow mark for each correct line if more than one line is drawn from any type of radiation box then all of those lines are wrong 3 (b) Gamma radiation will pass through the body (c) half (d) protons [6] M2. (a) cosmic rays radon gas (b) (i) Radioactive decay is a random process 9 (iii) 40 accept 59 their (b)(i) correctly calculated (iv) gamma the count stayed the same Page 20 of 3

21 or gamma does not have a charge accept gamma is an electromagnetic wave (so) gamma is not deflected / affected by the magnetic field accept magnet for magnetic field do not accept is not attracted to the magnet last two marks may be scored for an answer in terms of why it cannot be alpha or beta only answer simply in terms of general properties of gamma are insufficient (c) lead absorbs (some of the) radiation accept radiation cannot pass through (the lead) or less radiation emitted into the (storage) room (d) Should radioactive waste be dumped in the oceans [0] M3. (a) (i).25 (msv) any two from: (frequent) flying accept stated occupation that involves flying living at altitude living in areas with high radon concentrations accept a specific area, eg Cornwall living in a building made from granite (blocks) having more than the average number of X-rays or having a CT scan accept more medical treatments working in a nuclear power station accept any suggestion that could reasonably increase the level from a specific source (b) (i) to be able to see the effect of exposure (to radon gas) or as a control accept to compare (the effect of) exposure (with no exposure) 2 Page 2 of 3

22 increased levels of exposure increases the risk (of developing cancer) accept exposure (to radon gas) increases the risk smoking increases the (harmful) effect of radon answers that simply reproduce statistics are insufficient (c) LNT model risk increases with increasing radiation (dose) level accept in (direct) proportion accept low doses increase the risk (d) Radiation hormesis - low radiation (dose) levels reduce the risk two valid points made examples: animals have no choice and so should not be used should not make animals suffer better to experiment on animals than humans experiments lead to a better understanding / new knowledge experiments may lead to health improvement / cures for humans results for animals may not apply to humans is insufficient 2 [0] M4. (a) (i) 200 to 50 accept either order 5.3 accept values between 5.2 and 5.4 inclusive (iii) 5.3 accept values between 5.2 and 5.4 inclusive or their (a) (b) (i) Make the conveyor belt move more slowly lead Page 22 of 3

23 (c) Exposure increased the content of some types of vitamin. [6] M5. (a) 78 (b) atomic (c) (i) 3 correct order only 54 (iii) 32 (days) allow mark for showing 4 half-lives provided no subsequent step limits amount of iodine-3 / radioactive iodine that can be absorbed accept increases level of non-radioactive iodine in thyroid do not accept cancels out iodine-3 2 so reducing risk of cancer (of the thyroid) accept stops risk of cancer (of the thyroid) [8] M6. (a) (i) any one from: nuclear power (stations) accept nuclear waste accept coal power stations nuclear weapons (testing) accept nuclear bombs / fallout nuclear accidents accept named accident, eg Chernobyl or Fukushima accept named medical procedure which involves a radioactive source accept radiotherapy accept X-rays accept specific industrial examples that involve a radioactive source nuclear activity / radiation is insufficient smoke detectors is insufficient Page 23 of 3

24 (radioactive decay) is a random process accept an answer in terms of background / radiation varies (from one point in time to another) (b) any one from: (maybe) other factors involved accept a named sensible factor, eg smoking evidence may not be valid accept not enough data may not have (a complete) understanding of the process (involved) (c) (i) correct order only 84 (d) 3.8 (days) allow mark for showing correct method using the graph provided no subsequent steps correct answers obtained using numbers other than 800 and 400 gain 2 marks provided the method is shown 2 [9] M7. (a) neutrons and protons (b) 0 (+) (c) (i) total positive charge = total negative charge accept protons and electrons have an equal opposite charge (because) no of protons = no of electrons ion Page 24 of 3

25 positive (d) Marks awarded for this answer will be determined by the quality of communication as well as the standard of the scientific response. Examiners should apply a best-fit approach to the marking. 0 marks No relevant content Level ( 2 marks) There is a basic description of at least one of the particles in terms of its characteristics. Level 2 (3 4 marks) There is a clear description of the characteristics of both particles or a full description of either alpha or beta particles in terms of their characteristics. Level 3 (5 6 marks) There is a clear and detailed description of both alpha and beta particles in terms of their characteristics. examples of the physics points made in the response: structure alpha particle consists of a helium nucleus alpha particle consists of 2 protons and 2 neutrons a beta particle is an electron a beta particle comes from the nucleus penetration alpha particles are very poorly penetrating alpha particles can penetrate a few cm in air alpha particles are absorbed by skin alpha particles are absorbed by thin paper beta particles can penetrate several metres of air beta particles can pass through thin metal plate / foil beta particles can travel further than alpha particles in air beta particles can travel further than alpha particles in materials eg metals deflection alpha particles and beta particles are deflected in opposite directions in an electric field beta particles are deflected more than alpha particles alpha particles have a greater charge than beta particles but beta particles have much less mass or beta particles have a greater specific charge than alpha particles 6 [3] M8. (a) (i) nuclear reactor Page 25 of 3

26 star nuclei are joined (not split) accept converse in reference to nuclear fission do not accept atoms are joined (b) (i) any four from: neutron (neutron) absorbed by U (nucleus) ignore atom do not accept reacts do not accept added to forms a larger nucleus (this larger nucleus is) unstable (larger nucleus) splits into two (smaller) nuclei / into Ba and Kr releasing three neutrons and energy accept fast-moving for energy 56 (Ba) 4 57 (La) if proton number of Ba is incorrect allow mark if that of La is greater accept e for β scores 3 marks [0] Page 26 of 3

27 E. (a) Surprisingly nearly one third of students scored zero. (b) (c) (d) The vast majority of students were able to identify the correct reason for using gamma radiation. Over half of the students scored this mark. The most popular incorrect answer was all. Very poorly answered with over half of the students failing to score the mark. E2. (a) Just under two thirds of students correctly identified the two sources. X-rays was a commonly given incorrect answer. (b) (i) Just under two thirds of students gained this mark. (iii) (iv) Most students were able to correctly calculate the mean value. Only the more able students understood that the background count needed to be subtracted from 59. Many students gave the answer as 59 having ignored the background value. Just over half of students recognised that gamma was being emitted from the source, but few could give a valid explanation for this. A significant number of students simply wrote about the relative penetrating power of alpha, beta and gamma, with many of these students thinking that the gamma rays could pass through the actual magnets. The more able students explained that gamma rays were not deflected by the magnetic field, but only a few stated that the count had stayed the same. (c) (d) Nearly two thirds of the students gained this mark. Most of these gave an answer in terms of lead absorbing radiation. A common error was to say that the lead stopped the source from getting out. Just under half of the students identified the correct answer. Page 27 of 3

28 E3. (a) (i) It is perhaps surprising that only two-thirds of students scored this mark. Many students failed to read the question carefully and gave an answer of 2.5, the total dose received. Most students scored one mark, usually for a response associated with flying, but only half of which went on to score both marks. Most errors were due to lack of detail, for example, working in a power station rather than a nuclear power station, or simply living in an area with a high background level without specifying the source of that increased level. (b) (i) Almost two-thirds of students scored this mark. The most popular correct response was the idea of a control. The most common error was stating to compare smokers to non-smokers with no reference to radon gas. Just over half the students scored one mark for making the simple link between exposure to radon gas and the increased risk of cancer. Less than a third of students made a correct link to smoking increasing the harmful effect of the radon gas exposure. (c) (d) This question was generally well answered with just over half of students scoring both marks a further quarter of students scoring one mark. Those students scoring no marks often simply described the shape of the graph line rather than identifying the differences between the two models. Just over half of students scored both marks often producing a well written balanced view. A further third of students scored one mark. E4. (a) (i) This question was well done with two thirds of students scoring the mark. A common incorrect response was to give a range of 0 to 200. (iii) This was poorly done with only a third of students being able to obtain the correct time from the graph. Most students did not realise that they had been led to the value of the half-life in part (a).consequently many students began to calculate the half-life value again, mostly with little success. Only a quarter of students scored this mark. (b) (i) Only just over half the students scored this mark. Just over three fifths of students were able to correctly identify lead. (c) Most students were able to identify a correct conclusion to score this mark. Page 28 of 3

29 E5. (a) A majority of students scored this mark. (b) Again, a majority of students scored this mark. (c) (i) Over half of students scored zero, the most common error being an attempt to change mass and proton numbers in accordance with alpha decay. Students who got the proton number correct almost always scored full marks. The most common mistake made with the mass number was subtracting rather than adding. (iii) Under half of students correctly answered this for both marks. A minority of students scored one mark for correctly identifying four half-lives sufficiently well to gain credit. The most common mistake amongst students scoring one mark was to neglect to multiply 4 by 8, leaving 4 as the answer. Of the students who failed to score any marks 200/75 to give 6 days was one common misconception, another was in counting five half-lives, i.e. 200 as half-life, 600 as 2 half-lives etc. resulting in an answer of 40. A disappointing number of students could not multiply 4 8 correctly, giving answers of 24 or 36. Only 0% of students scored both marks for this question. Some students scored one mark for correctly stating that the tablets inhibit the absorption of I-3 but not stating the link to a reduced chance of developing cancer. Some students scored one mark for indicating that the tablets did reduce the chance of developing cancer but with incorrect reasoning. Two common misconceptions were that the tablet acted like a vaccination to prepare the body to deal with the radioactive iodine using anti-bodies, or that the non-radioactive iodine would in some way neutralise the radioactivity of I-3. E6. (a) (i) Surprisingly only just over half of students gained this mark, with the popular answers being nuclear power stations or nuclear weapons testing. X-Rays was also a common response. The common incorrect responses were smoke detectors and vague answers referring to medical uses without being specific. A significant number of students failed to see that man-made sources was in bold and responded with cosmic rays and rocks. Several students gave the correct response in terms of background radiation varying but relatively few gave the answer in terms of decay being a random process. Common incorrect answers referred to the teacher moving the experiment around the lab to cause the differences or to other radioactive sources being present at the times of the three readings, including the introduction of radioactive materials into the room and the presence of different food being present when the readings were taken. Many did use vary or changes but too many gave responses showing a complete lack of understanding of this process. (b) (c) (d) The most common correct response was other factors. When other factors were mentioned, it was usually smoking. Several students gave answers referring to the hereditary aspect of cancer. Very few answers talked about the validity of the evidence, or the sample size. The majority of the students gained both marks. Almost two thirds of the students gave the correct response of 3.8 days, with a few giving the answer as a fraction and one or two converting 0.8 days into hours and minutes. Nearly all correct answers used the counts of 800 and 400 to determine the half-life. A few misread the x axis scale and then answered 3.4 days and a few, after drawing correct lines then put down an incorrect answer. Common errors included believing the 222 of radon was important and so a line was drawn across from a count of 222 to give a half-life near 7 days. Page 29 of 3

30 E8. (a) (i) Nearly all students knew that nuclear fission takes place within a reactor and that nuclear fusion takes place within a star. Less than half of the students could state a way in which fusion differs from fission. Many statements referred to atoms or elements instead of nuclei. (b) (i) A nuclear equation representing fission was given and students were asked to use the information in the equation to describe the process of fission. This was well answered, with just under half of the students gaining all four marks. Many statements relating to fission were seen which ignored the given equation. For example two or three neutrons are released when the equation clearly showed three. Only a quarter of students could complete a nuclear equation depicting beta minus emission by adding subscripts for atomic number and a correct symbol for a beta particle. Many students are unclear concerning the symbol, subscript and superscript for a beta particle. Page 30 of 3

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