8.2 Nuclear Physics - Alpha, Beta, Gamma radiation - Qs · 8.2 Nuclear Physics - Alpha, Beta, Gamma...

of 26

8.2 Nuclear Physics - Alpha, Beta, Gamma radiation – Questions

Q1. (a) Which ionizing radiation produces the greatest number of ion pairs per mm in air?

Tick (✓) the correct answer.

α particles

β particles

γ rays

X−rays

(1)

(b) (i) Complete the table showing the typical maximum range in air for α and β particles.

Type of radiation Typical range in air / m

α

β

(2)

(ii) γ rays have a range of at least 1 km in air. However, a γ ray detector placed 0.5 m from a γ ray source detects a noticeably smaller count-rate as it is moved a few centimetres further away from the source.

Explain this observation.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(c) Following an accident, a room is contaminated with dust containing americium which is an α−emitter.

Explain the most hazardous aspect of the presence of this dust to an unprotected human entering the room.

___________________________________________________________________

___________________________________________________________________

of 26

___________________________________________________________________

___________________________________________________________________ (2)

(Total 6 marks)

Q2. A radioactive nucleus decays with the emission of an alpha particle and a gamma-ray photon.

(a) Describe the changes that occur in the proton number and the nucleon number of the nucleus.

proton number ______________________________________________________

nucleon number _____________________________________________________ (2)

(b) Comment on the relative penetrating powers of the two types of ionizing radiation.

___________________________________________________________________

___________________________________________________________________ (1)

(c) Gamma rays from a point source are travelling towards a detector. The distance from the source to the detector is changed from 1.0 m to 3.0 m.

Calculate

intensity of radiation at 3.0 m

intensity of radiation at 1.0 m

answer ____________________ (2)

(Total 5 marks)

Q3. A freshly prepared radioactive source that emits negatively charged beta particles (β–) has an activity of 120 Bq and a half-life of 12 h.

(a) (i) State the effect on the proton number Z and the nucleon number A when a β– particle is emitted.

______________________________________________________________

of 26

______________________________________________________________ (2)

(ii) Sketch, on the axes below, a graph that shows how the activity varies during the two days after the source was prepared.

(3)

(b) (i) The total energy released in each decay is 5.5 × 10–13 J. Calculate the initial energy produced each second by the source.

initial energy ____________________ J (1)

(ii) Figure 1 shows the energy spectrum for the beta particles emitted in the decay.

It shows that different energy beta particles are possible.

Figure 1

of 26

Explain why all the beta particles that are emitted do not have 5.5 × 10–13 J of energy.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(c) The probability of one of the radioactive atoms decaying each second is 1.6 × 10–5.

How many radioactive atoms are present when the activity is 120 Bq?

number of radioactive atoms ____________________ (1)

(d) A scientist undertaking an investigation places the freshly prepared source close to a Geiger-Müller tube as shown in Figure 2 and records a count rate of 50 counts per second.

Figure 2

State and explain two reasons why the measured count rate is lower than the activity of the source.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q4. A radium-288 nuclide ( ) is radioactive and decays by the emission of a β– particle to form an isotope of actinium (Ac).

of 26

(a) Complete the equation for this decay.

(3)

(b) β– decay is the result of a neutron within a nucleus decaying into a proton. Describe the change in the quark sub-structure that occurs during the decay.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(Total 4 marks)

Q5. Iodine-123 is a radioisotope used medically as a tracer to monitor thyroid and kidney functions. The decay of an iodine-123 nucleus produces a gamma ray which, when emitted from inside the body of a patient, can be detected externally.

(a) Why are gamma rays the most suitable type of nuclear radiation for this application?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) In a laboratory experiment on a sample of iodine-123 the following data were collected.

time/h 0 4 8 12 16 20 24 28 32

count-rate /counts s–1 512 410 338 279 217 191 143 119 91

Why was it unnecessary to correct these values for background radiation?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) On the axes provided in the diagram below, complete the graph of count-rate against time.

of 26

(2)

(d) Use your graph to find an accurate value for the half-life of iodine-123. Show clearly the method you use.

Half-life ____________________ (3)

(e) Give two reasons why radioisotopes with short half-lives are particularly suitable for use as a medical tracer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 11 marks)

of 26

Q6. A student has access to a radioactive source that decays by emitting alpha, beta and gamma radiation. The student wishes to investigate whether the count rate due to the gamma radiation varies with distance from the source according to an inverse square law and sets up the source and detector as shown in Figure 1.

(a) State and explain how the student can ensure that only gamma radiation is detected during the investigation.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) The corrected count rate due to gamma radiation is 64 counts per second at a distance of 50 mm from the source. Assuming that an inverse square law is obeyed calculate the expected corrected count rate at a distance of 80 mm from the source.

Count rate at 80 mm ____________________ (2)

(c) Using the data from part (b) sketch, on the axes in Figure 2, the graph the student would expect if an inverse square law were obeyed. The corrected count rate at 50 mm has been plotted already.

of 26

Figure 2 (2)

(Total 6 marks)

Q7. Thallium (Tl) decays to a stable form of lead (Pb) with the emission of a β– particle. Complete the equation below for this decay.

(Total 3 marks)

Q8. (a) (i) Alpha and beta emissions are known as ionising radiations. State and explain

why such radiations can be described as ionising.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

of 26

(ii) Explain why beta particles have a greater range in air than alpha particles.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(b) The figure below shows the variation with time of the number of Radon (220Ra) atoms in a radioactive sample.

(i) Use the graph to show that the half-life of the decay is approximately 53 s. Show your reasoning clearly.

(3)

(ii) The probability of decay (decay constant) for 220Ra is 1.3 × 10–2 s–1. Use data from the graph to find the activity of the sample at a time t = 72 s.

activity ____________________ (3)

(Total 10 marks)

Q9. (a) In a radioactivity experiment, background radiation is taken into account when

taking corrected count rate readings in a laboratory. One source of background radiation is the rocks on which the laboratory is built. Give two other sources of background radiation.

of 26

source 1 ___________________________________________________________

source 2 ___________________________________________________________ (1)

(b) A γ ray detector with a cross-sectional area of 1.5 × 10–3 m2 when facing the source is placed 0.18 m from the source. A corrected count rate of 0.62 counts s–1 is recorded.

(i) Assume the source emits γ rays uniformly in all directions. Show that the ratio

is about 4 × 10–3.

(2)

(ii) The γ ray detector detects 1 in 400 of the γ photons incident on the facing surface of the detector. Calculate the activity of the source. State an appropriate unit.

answer = ____________________ unit ___________ (3)

(c) Calculate the corrected count rate when the detector is moved 0.10 m further from the source.

of 26

answer = ____________________ counts s–1

(3) (Total 9 marks)

Q10. (a) (i) Explain what is meant by background radiation.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) Name a source of background radiation.

______________________________________________________________ (1)

(b) State the meaning of each of the terms in the equation A = λN

A _________________________________________________________________

___________________________________________________________________

λ _________________________________________________________________

___________________________________________________________________

N _________________________________________________________________

___________________________________________________________________ (3)

(Total 6 marks)

Q11. The graph below shows how the nucleon number A changes with proton number Z for the decay series that starts with uranium-238. The half-lives of each decay are also shown.

of 26

(a) How many alpha particles and beta particles are emitted when a uranium-238 nucleus decays to radon-222 (222Rn)?

Number of alpha particles _____________________________________________

Number of beta particles ______________________________________________ (2)

(b) How many neutrons are there in a nucleus of polonium-210 (210Po)?

___________________________________________________________________ (1)

of 26

(c) Identify the stable isotope that results from this decay chain.

___________________________________________________________________ (1)

(d) 214 g of bismuth-214 (214 Bi) contains 6.0 × 1023 atoms. A sample containing only bismuth-214 has an initial mass of 0.60 g.

(i) After what period of time will the mass of bismuth-214 present in the sample be 0.15 g?

(2)

(ii) Determine the number of bismuth-214 atoms present after this time. (1)

(iii) Calculate the activity of the bismuth-214 in the sample after this time. (4)

(iv) Explain how the total activity of the sample will be different from the value calculated in (iii).

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(v) The bismuth-214 decays into polonium-214. Explain why you would find very little polonium-214 if you were to analyse the sample.

______________________________________________________________

______________________________________________________________ (2)

(Total 15 marks)

Q12. (a) State which type of radiation, α, β or γ,

(i) produces the greatest number of ion pairs per mm in air,

______________________________________________________________

(ii) could be used to test for cracks in metal pipes.

______________________________________________________________

______________________________________________________________ (2)

(b) Specific radioisotope sources are chosen for tracing the passage of particular substances through the human body.

of 26

(i) Why is a γ emitting source commonly used?

______________________________________________________________

______________________________________________________________

(ii) State why the source should not have a very short half-life.

______________________________________________________________

______________________________________________________________

(iii) State why the source should not have a very long half-life.

______________________________________________________________

______________________________________________________________ (3)

(c) A detector, placed 0.20 m from a sealed γ ray source, receives a mean count rate of 2550 counts per minute. The experimental arrangement is shown in the diagram below. The mean background radiation is measured as 50 counts per minute.

Calculate the least distance between the source and the detector if the count rate is not to exceed 6000 counts per minute.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (5)

(Total 10 marks)

Q13. Potassium-42 decays with a half-life of 12 hours. When potassium-42 decays it emits β–

of 26

particles and gamma rays. One freshly prepared source has an activity of 3.0 × 107 Bq.

(a) To determine the dose received by a scientist working with the source the number of gamma ray photons incident on each cm2 of the body has to be known.

One in every five of the decaying nuclei produces a gamma ray photon. A scientist is initially working 1.50 m from the fresh source with no shielding. Show that at this time approximately 21 gamma ray photons per second are incident on each cm2 of the scientist's body.

(2)

(b) The scientist returns 6 hours later and works at the same distance from the source.

(i) Calculate the new number of gamma ray photons incident per second on each cm2 of the scientist's body.

(3)

(ii) At what distance from the source could the scientist now work and receive the original dose of 21 photons per second per cm2 .

(2)

(c) Explain why it is not necessary to consider the beta particle emission when determining the dose of radiation the scientist receives.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 9 marks)

Q14. (a) The exposure of the general public to background radiation has changed

substantially over the past 100 years. State one source of radiation that has contributed to this change.

___________________________________________________________________

___________________________________________________________________ (1)

(b) A student measures background radiation using a detector and determines that background radiation has a mean count-rate of 40 counts per minute. She then places a γ ray source 0.15 m from the detector as shown below.

of 26

With this separation the average count per minute was 2050.

The student then moves the detector further from the γ ray source and records the count-rate again.

(i) Calculate the average count-rate she would expect to record when the source is placed 0.90 m from the detector.

count-rate = ____________________ min–1

(3)

(ii) The average count per minute of 2050 was determined from a measurement over a period of 5 minutes. Explain why the student might choose to record for longer than 5 minutes when the separation is 0.90 m.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(iii) When the detector was moved to 0.90 m the count-rate was lower than that calculated in part (b)(i). It is suggested that the source may also emit β particles.

Explain how this can be checked.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

of 26

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(Total 7 marks)

Q15. (a) Calculate the radius of the U nucleus.

r0 = 1.3 × 10–15 m

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) At a distance of 30 mm from a point source of rays the corrected count rate is C. Calculate the distance from the source at which the corrected count rate is 0.10 C, assuming that there is no absorption.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) The activity of a source of β particles falls to 85% of its initial value in 52 s. Calculate the decay constant of the source.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(d) Explain why the isotope of technetium, 99Tc m, is often chosen as a suitable source of radiation for use in medical diagnosis.

You may be awarded additional marks to those shown in brackets for the quality of written communication in your answer.

of 26

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 10 marks)

Q16. An isotope of technetium is a gamma emitter used by doctors as a tracer in the human body. It is injected into the patient’s blood stream. Scanners outside the body measure the gamma activity, enabling the blood flow to be monitored.

(a) The graph shows the variation of activity with time, t, for a sample of the isotope.

(i) Use data from the graph to determine the half-life of the technetium isotope. (3)

(ii) The decay constant of the technetium isotope is 3.2 × 10−5 s−1. Use data from the graph and the equation A = λN to calculate the number of nuclei of the radioactive technetium isotope present at time t = 0.

(2)

(b) (i) State why an alpha emitter would not be suitable in this application.

______________________________________________________________

______________________________________________________________

of 26

(1)

(ii) State why the half-life of the technetium isotope makes it suitable for this application.

______________________________________________________________

______________________________________________________________ (1)

(c) State and explain how the presence of the technetium isotope may do some damage to the patient.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 9 marks)

Q17. The radioisotope iodine-131 ( ) is used in medicine to treat over-active thyroid glands. It decays into an isotope of xenon (Xe) by β– emission with a half-life of 8.1 days. The xenon subsequently emits a γ ray.

(a) Explain what is meant by:

(i) isotope;

______________________________________________________________

______________________________________________________________ (2)

(ii) half-life.

______________________________________________________________

______________________________________________________________ (1)

(b) Write down the equation which represents the nuclear reaction. (3)

(c) Calculate the time (in days) for a sample of iodine to decay to 1% of its initial activity.

(4)

(d) State and explain which decay product can be detected outside the body during treatment.

___________________________________________________________________

of 26

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q18. is an isotope of uranium which decays through a decay chain to the isotope of lead, , which is stable. During the sequence of decays, both alpha particles and beta

particles are emitted.

(a) (i) represents an alpha particle.

State the values of:

A ___________________________________

Z ___________________________________ (1)

(ii) represents a beta particle.

State the values of:

A ___________________________________

Z ___________________________________ (1)

(iii) State and explain how many alpha particles are emitted during the decay chain

between .

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(iv) State and explain how many beta particles are emitted during the decay chain between and .

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(b) The decay of uranium can be used to measure the age of rocks. A rock, which

of 26

contained N0 atoms of when it was formed, will contain NU atoms of the isotope at a later time t.

(i) The relationship between N0, NU and t is:

NU = N0e–λt

State the meaning of the decay constant, λ.

______________________________________________________________

______________________________________________________________ (1)

(ii) Because the half-life of is much longer than that of any other member of the decay chain, it may be assumed that the number of atoms of present at time t is equal to the number of atoms which have decayed. Show that the ratio of the number of lead atoms (NP) to the number of uranium atoms at time t is given by:

= eλt – 1 (2)

(iii) The half-life of is 4.5 × 109 year. Calculate the age of a rock sample which contains 4.2 parts per million of and 0.62 parts per million of

. (4)

(iv) The above analysis assumes that the rock contained no lead when it was formed. State and explain the effect on the estimated age if the rock had contained lead when it was formed.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(v) State reasons why the measurement of the amount of uranium in a rock sample would be inaccurate when performed by a radiation counting technique.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

of 26

(2) (Total 17 marks)

Q19. The diagram below shows an arrangement used to maintain a constant thickness of sheet paper or steel as it is being rolled. A radioactive source and detector are used to monitor the thickness.

(a) Explain briefly how this arrangement works.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Alpha, beta or gamma sources could be selected for use in such an arrangement.

State which source should be selected in each case and explain briefly why the others would not be suitable.

Paper:

Source selected _____________________________________________________

Reasons why the others are unsuitable ___________________________________

___________________________________________________________________

___________________________________________________________________

Steel:

Source selected _____________________________________________________

Reasons why the others are unsuitable ___________________________________

___________________________________________________________________

___________________________________________________________________ (4)

of 26

(c) Cobalt-60 is commonly used as a source in such applications. This has a half-life of 5.3 years. When fresh the source contains 5.0 × 1020 radioactive atoms.

For it to be useful the source has to have an activity of at least 1.5 × 1012 Bq.

(i) What is meant by an activity of 1 Bq?

______________________________________________________________

______________________________________________________________ (1)

(ii) Draw a graph showing the number of radioactive atoms in the source over a period of 3 half-lives. Include suitable scales on the axes.

(2)

(iii) Determine the decay constant of cobalt-60 in s–1. (2)

(iv) After what time will it be necessary to replace the source? (3)

(Total 15 marks)

Q20. (a) Bi can decay into Pb by a β– followed by an α decay, or by an α followed by a

β– decay. One or more of the following elements is involved in these decays:

Write out decay equations showing each stage in both of these decays.

First decay path Second decay path

of 26

(6)

(b) (i) Describe how you would perform an experiment that demonstrates that gamma radiation obeys an inverse square law.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(ii) Explain why gamma radiation obeys an inverse square law but alpha and beta radiation do not.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (9)

(Total 15 marks)

Q21. The actinium series of radioactive decays starts with an isotope of uranium, nucleon (mass) number 235, proton (atomic) number 92.

Which line in the table shows the nucleon number and proton number of the isotope after the emission of 5 α particles and 2 β– particles?

of 26

Nucleon number proton number

A 213 82

B 215 80

C 215 84

D 227 87

(Total 1 mark)

Q22. β particles are emitted from a radioactive source in a school laboratory.

What is correct for these particles?

A A strong magnetic field will not deflect them.

B They are absorbed by aluminium.

C They do not damage human tissue.

D Their range in air is shorter than that of α particles.

(Total 1 mark)

Q23. An alpha particle moves at one-tenth the velocity of a beta particle. They both move through the same uniform magnetic field at right angles to their motion.

The magnitude of the ratio is

A

B

C

D (Total 1 mark)

Q24. A Geiger counter is placed near a radioactive source and different materials are placed between the source and the Geiger counter.

of 26

The results of the tests are shown in the table.

Material Count rate of Geiger counter / s–1

None 1000

Paper 1000

Aluminium foil 250

Thick steel 50

What is the radiation emitted by the source?

A α only

B α and γ

C α and β

D β and γ (Total 1 mark)

8.2 Nuclear Physics - Alpha, Beta, Gamma radiation - Qs · 8.2 Nuclear Physics - Alpha, Beta, Gamma...

Documents

Transcript of 8.2 Nuclear Physics - Alpha, Beta, Gamma radiation - Qs · 8.2 Nuclear Physics - Alpha, Beta, Gamma...