Name: CS P1 F Radioactivity. Date: Time: 29 minutes. Total marks available: 29. Total marks achieved: Questions

Transcription

1 Name: CS P1 F Radioactivity Date: Time: 29 minutes Total marks available: 29 Total marks achieved: Questions

2 Q1. An atom contains electrons, neutrons and protons. Use words from the box to complete the sentences. neutral much larger than a neutron positive negative much smaller than a neutron the same size as a neutron (i) The charge on an electron is... (ii) An electron has a mass that is... Q2. Other unstable isotopes emit alpha particles. Which of these describes an alpha particle? A B C D a hydrogen nucleus a hydrogen atom a helium nucleus a helium atom (Total for question = 1 mark) Q3. Alpha, beta and gamma are types of ionising radiation.

3 State twoways in which gamma radiation is different from alpha radiation. (2) Q4. Carbon-14 is a radioactive isotope that occurs naturally. Scientists use carbon-14 to help find the age of old pieces of wood. This technique is called carbon dating. It uses the idea of half-life. Sketch a graph to show how the activity of a radioactive isotope changes with time. Use the axes below. Start your line from point P. (3)

4 Q5. An isotope of krypton, krypton-89, is produced in a nuclear reactor. A nucleus of this isotope can be represented as Describe the structure of a nucleus of krypton-89. (4) Q6. The diagram shows the structure of an atom. (i) Complete the sentence by putting a cross ( ) in the box next to your answer. The size of the charge on each electron is A a third of the charge on the proton

5 B half the charge on the proton C the same as the charge on the proton D twice the charge on the proton (ii) Complete the sentence by putting a cross ( ) in the box next to your answer. The atomic number of a neutral atom is always the same as the number of A electrons B electrons and neutrons C protons and neutrons D neutrons Q7. Particles released during radioactive decay can have different energies. A suitable unit for these energies is MeV. For one type of decay, the particles released have energies between 4.0 MeV and 10.0 MeV. The graph shows how far the particles with these energies travel in air. (i) State the name of this type of particle. (ii) Use information from the graph to describe how the distance travelled in air depends on the

6 energy of the particle. (2) Q8. Uranium-238 is an isotope of uranium. It may undergo either radioactive decay or nuclear fission. A nucleus of uranium-238 is shown as Q in the chart. State two letters from the chart which show isotopes of the same element....and.... Q9.

7 Choose words from the box to complete the following sentences. Words may be used once, more than once or not at all. The radiation that is a wave is... The particle that is negatively charged is... Q10. Alpha, beta and gamma are types of ionising radiation. Explain how an atom becomes ionised by radiation. (2) Q11. Which of these is correct for half-life? Put a cross ( ) in the box next to your answer. A It is half the time for all the atoms to decay B It is the time it takes for an atom to half decay C It is the time it takes for half an atom to decay

8 D It is the time it takes for half the atoms to decay Q12. The graph shows how the activity of a sample of a radioactive material changes with time. The sample has an initial activity of 80 counts per minute. (i) Use the graph to find the half-life of the material. half life =...days (ii) Another sample of the material has an initial count rate of 40 counts per minute. Sketch, on the same axes, the activity of this sample for the first 4 days. (2) Q13. Everyone is exposed to background radiation. Some of this radiation comes from natural

9 sources. (i) One example of a source of background radiation that does not occur naturally is radiotherapy. State oneother source of background radiation that does not occur naturally. (ii) Radon gas is a natural source of background radiation. In some parts of the country, a lot of the background radiation comes from radon gas. Explain why there is no radon gas in some other parts of the country. (2) Examiner's Report Q1. (i) Most candidates knew that electrons had a negative charge and so scored the mark for this question. (ii) The majority of candidates knew that the mass of an electron is much smaller than the mass of a neutron. Q2. No Examiner's Report available for this question

10 Q3. As expected here, the vast majority of candidates were able to state two ways in which gamma radiation is different from alpha radiation. Results Plus: Examiner Comments Two clear differences are given here, penetrating power and ionising ability. This answer scored 2 marks. Results Plus: Examiner Comments This response gives only one difference, to do with penetrating power so scored only 1 mark. Q4. To gain full credit for this sketch of a decay curve, the axes needed to be labelled. The label or the unit was acceptable. The decay curve had to be the correct shape and not touch the time axis.

11 Results Plus: Examiner Comments The y-axis shows the correct unit and the time axis shows the label and the unit. The curve is the correct shape and is just smooth enough to be acceptable. It does not reach the time axis. The other information, to do with half-life was good but irrelevant here. This response scored all 3 marks. Q5. Many candidates scored very well on this question. The easiest way to score full marks in this question was to write down the number of protons = 36 and to calculate the number of neutrons i.e = 53 neutrons. Weaker candidates often misread the question and tried to give the structure of the atom including the electron configuration.

12 Results Plus: Examiner Comments This type of response was fairly common. Despite the confusion about nucleon and proton numbers this response scored 2 marks for correctly stating the names of two particles in the nucleus. Results Plus: Examiner Comments An example of one of the many responses that scored full marks. Q6. No Examiner's Report available for this question Q7.

13 (i) This item asked for inference from the data given on a table. This proved to be an item of high discrimination with only the more able really successful in relating the distance travelled in air to the range expected of the different radioactive particles. Results Plus: Examiner Comments Some candidates arrived at the correct answer presumably by a process of elimination! (ii) The descriptions of a relationship shown on a graph were limited. Results Plus: Examiner Comments Most, like this example, managed to score the first mark. Results Plus: Examiner Comments Comparatively few made any attempt to go further either to describe the curved nature (as here) or to assume it was straight and give a value for the gradient. This example scored 2 marks.

14 Q8. No Examiner's Report available for this question Q9. Whilst most got the two responses correct a significant number of candidates misidentified the negatively charged particle. Results Plus: Examiner Comments There were not many incorrect responses to this question; this was the most common. Results Plus: Examiner Tip Think clearly and carefully. Positrons are the antiparticles of electrons; so if electrons are negatively charged, positrons must be positively charged. Q10. In explaining how atoms can become ionised by radiation, candidates were expected to know that the radiation causes the atom to lose or gain electrons. The majority of candidates scored at least 1 mark here with a large number going on to score both marks.

15 Results Plus: Examiner Comments This clearly expresses the idea that the radiation causes the atom to lose an electron. It was awarded 2 marks. Q11. No Examiner's Report available for this question Q12. (ii) This item tested the ability to use data to construct a graphical representation of the effect of a change in initial conditions. Parts 6ci and 6cii appear together. A large majority correctly identified the half-life as 2 days, in part i, but comparatively few knew how to use this with different initial conditions for part ii.

16 Results Plus: Examiner Comments Despite the wobbly line this was a good 'sketch'as it included the important points at 40, 20 and 10 which showed the shape of the curve. It was good enough to score both of the 2 marks. Perhaps the most unusual answer was this.

17 Results Plus: Examiner Comments It scored 0 for part ii. Q13. (i) Many candidates did not appreciate that the question asked for a source of background radiation that does not occur naturally, which ruled out cosmic rays, food, etc. This question also showed that a significant number of candidates believe that chemotherapy is radioactive rather than being treatment by drugs. The most frequently seen correct answer was X-ray (machines). (ii) The fact that radon gas originates in granite rocks was known by surprisingly few candidates. However, if the origin was known then it easily explained why some parts of the country did not have radon and this gave candidates the opportunity of scoring both marks.

18 Results Plus: Examiner Comments Power plants were quite often believed to be the origin of radon gas. No marks were awarded. Results Plus: Examiner Comments This is a rare example where 1 mark was awarded. The candidate knows the origin of radon gas but does not explain why it is not found in some parts of the country. Mark Scheme Q1. Answer Acceptable answers Mark (i) negative (ii) (much) smaller than a neutron

19 Q2. Q3. (i) Answer Acceptable answers Mark Any twoof: Reverse arguments (2) Gamma is a wave Alpha is a helium nucleus Alpha is charged Alpha has a mass Gamma penetrates further/ highly Gamma weakly ionising Gamma travels faster em radiation Gamma has no charge Gamma has no mass examples of penetrating power alpha highly ionising ignore vague comments eg stronger Ignore uses and dangers Q4. Answer Acceptable answers Mark axes labelled correctly With label or unit activity / Bq / count rate ignore radioactivity time/ seconds/ any time unit (3) correct shaped smooth curve line does not reach zero activity

20 Q5. Q6. Answer Acceptable answers Mark (i) Cthe same as the charge on the proton (ii) Aelectrons Q7.

21 Answer Acceptable answers Mark (i) alpha Alpha ray, alpha particle, α Ignore capital letters (ii) A description including two of (2) one increases as other increases rate of increase is in the range from 1.17 to 1.33 (cm/mev) range gradually increases more with energy the particles with higher energy travel further accept values quoted from graph not (quite) linear/not proportional /curves upwards accept values quoted from graph Q8. Answer Acceptable answers Mark P and M one mark for a pair OR OR OR M and P N and Q Q and N Q9. Q10. Answer Acceptable answers Mark An explanation linking: (2)

22 electron(s) is/are lost/gained do not allow positive electron knocked off / removed/ released Q11. Answer Acceptable answers Mark D It is the time it takes for half the atoms to decay Q12. Answer Acceptable answers Mark i (days) ii Ignore any part of line after 4 days plotting (0,40), (2,20 ) and (4,10) OR ANYline which passes through those coordinates (2) smooth curve through those points Q13. Answer Acceptable answers Mark any one of nuclear weapons (tests) nuclear X-ray (machines) / smoke alarms/ power plants (medical)

23 Powered by TCPDF ( (i) nuclear/ radioactive waste tracers/technetium (ii) an explanation linking: comes from granite / rocks none/ less of these (rocks) in some areas in some areas/cornwall/aberdeen (2) the second mark is dependent on the first.