Edexcel IGCSE Physics: Double Science Past Paper PDF

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Physics: Double Your notes Science Properties of Radiation Contents Atomic Structure Isotopes Types of Radiation Core Practical: Investigating Radi...

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Physics: Double Your notes Science Properties of Radiation Contents Atomic Structure Isotopes Types of Radiation Core Practical: Investigating Radiation Decay Equations Detecting Radiation Page 1 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Atomic Structure Your notes Atomic structure Atoms are the building blocks of all matter They are incredibly small, with a radius of only 1 × 10-10 m This means that about one hundred million atoms could fit side by side across your thumbnail Atoms have a tiny, dense nucleus at their centre, with electrons orbiting around the nucleus The radius of the nucleus is over 10,000 times smaller than the whole atom, but it contains almost all of the mass of the atom Atomic structure of lithium Diagram showing the structure of a Lithium atom. If drawn to scale then the electrons would be around 100 metres away from the nucleus! Particles in the atom The nucleus contains: Protons - positively charged particles with a relative atomic mass of one unit Neutrons – no charge, and also with a relative atomic mass of one unit Almost all of the atom is empty space, but moving around the nucleus there are: Electrons – negative charge with almost no mass (1/2000 the mass of a proton or neutron) The properties of each of the particles are shown in the table below: Table of particle properties Particle Location Relative charge Relative mass Page 2 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources proton in the nucleus +1 1 Your notes neutron in the nucleus 0 1 electron orbiting the nucleus −1 1/2000 (negligible) Charge in the atom Although atoms contain particles of different charge, the total charge within an atom is zero This is because the number of electrons is equal to the number of protons The following table sets out the calculation of the total charge in the lithium atom in the diagram above: Calculating total charge table Number of number × relative Particle Relative charge particles in lithium Total charge charge atom proton +1 3 +3 neutron 0 4 0 (+3) + 0 + (−3) = 0 electron −1 3 −3 If an atom loses electrons, then it is said to be ionised Symbols are used to describe particular nuclear by their element symbol, atomic number and mass number This notation is called nuclear notation Page 3 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Carbon 12 in nuclear notation Page 4 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes A nucleus of carbon-12 is shown below. How many electrons are there in an atom of carbon-12? Answer: Step 1: Count the number of protons in the carbon nucleus There are 6 protons in the carbon atom Step 2: Determine the number of electrons Remember, the number of electrons in an atom is equal to the number of protons Therefore there must be 6 electrons in the carbon atom Examiner Tip You may have noticed that the number of electrons is not part of the mass number. This is because electrons have a tiny mass compared to neutrons and protons. We say their mass is negligible when compared to the particles in the nucleus. Page 5 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Atomic & Mass Number Atomic number Your notes The number of protons in an atom is called its atomic number (it can also be called the proton number) Elements in the periodic table are ordered by their atomic number Therefore, the number of protons determines which element an atom is The atomic number of a particular element is always the same For example: Hydrogen has an atomic number of 1. It always has just one proton Sodium has an atomic number of 11. It has 11 protons Uranium has an atomic number of 92. It has 92 protons The atomic number is also equal to the number of electrons in an atom This is because atoms have the same number of electrons and protons in order to have no overall charge Mass number The total number of particles in the nucleus of an atom is called its mass number (it can also be called the nucleon number) The mass number is the number of protons and neutrons in the atom The number of neutrons can be found by subtracting the atomic number from the mass number number of neutrons = mass number – atomic number For example, if a sodium atom has a mass number of 23 and an atomic number of 11, then the number of neutrons would be 23 – 11 = 12 Nuclear notation The mass number and atomic number of an atom are shown by writing them with the atomic symbol This is called nuclear notation Here are three examples: Examples of nuclear notation for atoms of Hydrogen, Sodium and Uranium Page 6 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The top number is the mass number This is equal to the total number of particles (protons and neutrons) in the nucleus The lower number is the atomic number Your notes This is equal to the total number of protons in the nucleus The atomic and mass number of each type of atom in the examples above is shown in this table: Number of protons, neutrons & electrons table Number of neutrons Number of protons Number of electrons Atom (mass number − atomic (atomic number) (same as atomic number) number) hydrogen 1 1 1 sodium 11 12 11 uranium 92 143 92 Page 7 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes The element symbol for gold is 197 Au. 79 How many protons, neutrons and electrons are in an atom of gold? number of protons number of neutrons number of electrons A. 79 79 79 B. 197 79 118 C. 118 118 79 D. 79 118 79 ANSWER: D Step 1: Determine the atomic and mass number The gold atom has an atomic number of 79 (lower number) and a mass number of 197 (top number) Step 2: Determine the number of protons The atomic number is equal to the number of protons An atom of gold has 79 protons Step 3: Calculate the number of neutrons The mass number is equal to the number of protons and neutrons The number of neutrons is equal to the mass number minus the atomic number number of neutrons = 197 − 79 = 118 An atom of gold has 118 neutrons Step 4: Determine the number of electrons An atom has the same number of protons and electrons An atom of gold has 79 electrons Page 8 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Isotopes Your notes Isotopes For a particular element, the number of protons is always the same, but the number of neutrons can be different This is because the number of protons determines the element e.g. carbon atoms have 6 protons and iron atoms have 26 protons An isotope is defined as: An atom, or atoms, of the same element that have an equal number of protons but a different number of neutrons Each element can have more than one isotope Isotopes of hydrogen Some isotopes are more unstable than others due to the imbalance of protons and neutrons, which means Page 9 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources They may be more likely to decay They may be less likely to occur naturally For example, about 2 in every 10 000 atoms of hydrogen are the isotope deuterium Your notes The isotope tritium is even rarer (about 1 in every billion billion atoms of hydrogen) Worked example State the number of protons, neutrons and electrons in these two isotopes of chlorine: 35 Cl , 37 Cl 17 17 Answer: Step 1: Determine the number of protons The atomic number is the number of protons Both chlorine-35 and chlorine-37 have 17 protons Step 2: Determine the number of neutrons The mass number is the number of protons and neutrons Number of neutrons in chlorine-35 = 35 − 17 = 18 Number of neutrons in chlorine-37 = 37 − 17 = 20 Step 3: Determine the number of electrons The number of electrons is equal to the number of protons Both chlorine-35 and chlorine-37 have 17 electrons Page 10 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Types of Radiation Your notes Types of radiation Some atomic nuclei are unstable and radioactive This is because of an imbalance of protons or neutrons in the nucleus Carbon-14 is an example of an isotope of carbon which is unstable This is because it has two extra neutrons compared to a stable nucleus of carbon-12 Stable and unstable isotopes of carbon Carbon-12 is stable, whereas carbon-14 is unstable because it has two extra neutrons Unstable nuclei can emit radiation to become more stable Radiation can be in the form of a high-energy particle or wave This process is known as radioactive decay As the radiation moves away from the nucleus, it takes some energy with it This makes the nucleus more stable Radioactive decay of a nucleus Page 11 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Unstable nuclei decay by emitting high energy particles or waves When an unstable nucleus decays, it emits radiation The different types of radiation that can be emitted are: Alpha (α) particles Beta (β-) particles Gamma (γ) radiation These changes are spontaneous and random Worked example Which of the following statements is not true? A Isotopes can be unstable because they have too many or too few neutrons B The process of emitting particles or waves of energy from an unstable nucleus is called radioactive decay C Scientists can predict when a nucleus will decay D Radiation refers to the particles or waves emitted from a decaying nucleus ANSWER: C Answer A is true. The number of neutrons in a nucleus determines the stability Answer B is true. This is a suitable description of radioactive decay Answer D is true. Radiation is about emissions. It is different to radioactive particles Answer C is not true Radioactive decay is a random process It is not possible to predict precisely when a particular nucleus will decay Page 12 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes The terms unstable, random and decay have very particular meanings in this topic. Remember to use them correctly when answering questions! Page 13 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Properties of alpha, beta and gamma radiation Alpha particles Your notes The symbol for alpha is α An alpha particle is the same as a helium nucleus This is because it consists of two neutrons and two protons Beta particles The symbol for beta is β− Beta particles are high-energy electrons They are produced in nuclei when a neutron changes into a proton and an electron Gamma rays The symbol for gamma is γ Gamma rays are electromagnetic waves They have the highest energy of the different types of electromagnetic waves Alpha, beta & gamma radiation Alpha particles, beta particles and gamma waves can be emitted from unstable nuclei Properties of alpha, beta & gamma Alpha (α), beta (β) and gamma (γ) radiation can be identified by their: Nature (what type of particle or radiation they are) Ionising ability (how easily they ionise other atoms) Penetrating power (how far can they travel before they are stopped completely) Page 14 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Alpha, beta and gamma penetrate materials in different ways This means they are stopped, or reduced, by different materials Penetrating power of alpha, beta and gamma Your notes Alpha, beta and gamma are different in how they penetrate materials. Alpha is the least penetrating, and gamma is the most penetrating Alpha is stopped by paper, whereas beta and gamma pass through it Beta is stopped by a few millimetres of aluminium Gamma rays can pass through aluminium but are only partially stopped by thick lead Summary of the properties of nuclear radiation Particle Nature Range in air Penetrating power Ionising ability helium nucleus (2 protons, 2 low; stopped by a thin sheet of Alpha (α) a few cm high neutrons) paper moderate; stopped by a few high-energy Beta (β) a few 10s of cm mm of aluminium foil or moderate electron Perspex Page 15 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources electromagnetic high; reduced by a few cm of Gamma (γ) infinite low wave lead Your notes Worked example A student has an unknown radioactive source. They are trying to work out which type of ionising radiation is being emitted. They measure the count rate, using a Geiger-Muller tube, when the source is placed behind different materials. Their results are recorded in a table. no material thin sheet of paper 5 mm aluminium foil 5mm lead plate between source between source and between source and between source and detector detector detector and detector Count-rate 4320 4218 256 34 Which type(s) of ionising radiation is/are emitted by the source? A Alpha particles B Beta particles C Gamma rays D Alpha, beta and gamma radiation ANSWER: B The answer is not A or D because the radiation passed through the paper almost unchanged This means it is not alpha as alpha is stopped by a thin sheet of paper The answer is not C because the aluminium decreased the count rate significantly This means it is not gamma as gamma penetrates aluminium Therefore, the source must be beta particles Page 16 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Core Practical: Investigating Radiation Your notes Core practical 13: investigating radiation Aim of the experiment The aim of this experiment is to investigate the penetration powers of different types of radiation using either radioactive sources or simulations Variables: Independent variable = Absorber material Dependent variable = Count rate Control variables: Radioactive source Distance of GM tube to source Location / background radiation Equipment List Equipment Purpose radioactive sources (α, β and γ) to use as a source of radioactive emission to measure the distance between the source and ruler detector mount for radioactive source to secure the source in place Geiger-Muller tube and counter to measure the count rate of a radioactive source tongs to safely handle the sources at a distance selection of absorbing materials (paper, aluminium to place between the source and detector to foil, lead) investigate effect on count rate lead-lined containers for radioactive sources to store sources in when not in use Resolution of measuring equipment: Ruler = 1 mm Geiger-Müller tube = 0.01 μS/hr Method Page 17 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Apparatus for investigating the penetrating powers of different types of radiation 1. Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a period of one minute 2. Repeat this three times, and take an average. Subtract this value from all subsequent readings. 3. Place a radioactive source a fixed distance of 3 cm away from the tube and take another reading of count rate over a period of one minute 4. Take a set of absorbers, i.e. some paper, several different thicknesses of aluminium (increasing in 0.5 mm intervals) and different thicknesses of lead 5. One at a time, place these absorbers between the source and the tube and take another reading of count rate over a period of one minute 6. Repeat the above experiment for other radioactive sources Analysis of results If the count rate is similar to background levels (allowing for a little random variation), then the radiation has all been absorbed Note: some sources will emit more than one type of radiation If the count rate reduces when paper is present, the source is emitting alpha If the count rate reduces when a few mm of aluminium is present, then the source is emitting beta If some radiation is still able to penetrate a few mm of lead, then the source is emitting gamma Page 18 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Penetrating power of alpha, beta and gamma radiation Evaluating the experiment Systematic Errors: Make sure that the sources are stored well away from the counter during the experiment Conduct all runs of the experiment in the same location to avoid changes in background radiation levels Random Errors: The accuracy of such an experiment is improved with using reliable sources with a long half-life and an activity well above the natural background level Safety considerations When not using a source, keep it in a lead-lined container When in use, try and keep a good distance (a metre or so) between yourself and the source When handling the source, do so using tweezers (or tongs) and point the source away from you Page 19 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes When answering questions about the core practicals you could try to remember the acronym SCREAMS: S: Which variable will you keep the same C: which variable should you change R: what will you do to make your experiment reliable E: what special equipment and equations are required A: how will you analyse your results M: which variable will you measure S: what safety precautions will you take? Page 20 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Decay Equations Your notes Alpha, beta, gamma & neutron emission Alpha decay During alpha decay, an alpha particle is emitted from an unstable nucleus A completely new element is formed in the process Alpha decay usually happens in large unstable nuclei, causing the overall mass and charge of the nucleus to decrease An alpha particle is a helium nucleus It is made of 2 protons and 2 neutrons When the alpha particle is emitted from the unstable nucleus, the mass number and atomic number of the nucleus changes The mass number decreases by 4 The atomic number decreases by 2 Alpha decay can be represented by the following nuclear equation: AX → A − 4Y + 4α Z Z −2 2 Where: AX is the initial element X with mass number A and atomic number Z Z A − 4Y is the new element Y Z −2 Page 21 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4α is an alpha particle 2 Beta decay Your notes During beta decay, a neutron changes into a proton and an electron The electron is emitted and the proton remains in the nuclei A completely new element is formed because the atomic number changes Beta decay often happens in unstable nuclei that have too many neutrons. The mass number stays the same, but the atomic number increases by one A beta particle is a high-speed electron It has a mass number of 0 This is because the electron has a negligible mass, compared to neutrons and protons Therefore, the mass number of the decaying nuclei remains the same Electrons have an atomic number of -1 This means that the atomic number of the new nucleus will increase by 1 to balance the overall atomic number before and after the decay Beta decay can be represented by the following nuclear equation: AX → AY + 0β Z Z +1 −1 Where: AX is the initial element X with mass number A and atomic number Z Z AY is the new element Y Z +1 0β is a beta particle −1 Gamma decay During gamma decay, a gamma ray is emitted from an unstable nucleus This process makes the nucleus less energetic but does not change its structure Page 22 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Gamma decay does not affect the mass number or the atomic number of the radioactive nucleus, but it does reduce the energy of the nucleus The gamma ray that is emitted has a lot of energy, but no mass or charge Gamma decay can be represented by the following nuclear equation: AX → AX + 0 γ Z Z 0 Where: AX is the element X with mass number A and atomic number Z Z 0 γ is a gamma ray 0 Notice that the mass number and atomic number of the unstable nucleus remains the same during the decay Neutron emission A small number of isotopes can decay by emitting neutrons When a nucleus emits a neutron: The atomic number (number of protons) does not change The mass number (total number of nucleons) decreases by 1 Neutron emission can be represented by the following nuclear equation: AX → A − 1X + 1n Z Z 0 Where: AX is the element X with mass number A and atomic number Z Z 1n is a neutron 0 Notice that the atomic number remains the same during the decay but the mass number has changed Page 23 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources This means an isotope of the original element has formed Your notes Examiner Tip It is easy to forget that an alpha particle is a helium nucleus. The two are interchangeable, so don’t be surprised to see either used in the exam. You are not expected to know the names of the elements produced during radioactive decays, but you do need to be able to calculate the mass and atomic numbers by making sure they are balanced on either side of the reaction. Page 24 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Nuclear decay equations Radioactive decay events can be shown using nuclear decay equations Your notes A decay equation is similar to a chemical reaction equation as the particles present before the decay are shown before the arrow the particles produced in the decay are shown after the arrow In a decay equation: the sum of the mass numbers before and after the reaction must be the same the sum of the atomic numbers before and after the reaction must be the same The following decay equation shows polonium-212 undergoing alpha decay 212 Po → 208 Pb + 4α 84 82 2 When a nucleus of polonium-212 decays, a nucleus of lead-208 forms and an alpha particle is emitted To check if the equation is balanced: mass number: 212 = 208 + 4 atomic number: 84 = 82 + 2 The sum of the numbers are the same on each side, so the equation is balanced Page 25 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes A nucleus with 84 protons and 126 neutrons undergoes alpha decay. It forms lead, which has the element symbol Pb. A. 206 Pb 82 B. 208 Pb 82 C. 210 Pb 84 D. 214 Pb 86 Which of the isotopes of lead pictured is the correct one formed during the decay? ANSWER: A Step 1: Calculate the mass number of the original nucleus The mass number is equal to the number of protons plus the number of neutrons The original nucleus has 84 protons and 126 neutrons 84 + 126 = 210 The mass number of the original nucleus is 210 Step 2: Calculate the new atomic number The alpha particle emitted is made of two protons and two neutrons Protons have an atomic number of 1, and neutrons have an atomic number of 0 Removing two protons and two neutrons will reduce the atomic number by 2 84 – 2 = 82 The new nucleus has an atomic number of 82 Step 3: Calculate the new mass number Protons and neutrons both have a mass number of 1 Removing two protons and two neutrons will reduce the mass number by 4 210 – 4 = 206 The new nucleus has a mass number of 206 Page 26 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes A nucleus with 11 protons and 13 neutrons undergoes beta decay. It forms magnesium, which has the element symbol Mg. A. 20 Mg 9 B. 24 Mg 10 C. 23 Mg 11 D. 24 Mg 12 Which is the correct isotope of magnesium formed during the decay? ANSWER: D Step 1: Calculate the mass number of the original nucleus The mass number is equal to the number of protons plus the number of neutrons The original nucleus has 11 protons and 13 neutrons 11 + 13 = 24 The mass number of the original nucleus is 24 Step 2: Calculate the new atomic number During beta decay a neutron changes into a proton and an electron The electron is emitted as a beta particle The neutron has an atomic number of 0 and the proton has an atomic number of 1 So the atomic number increases by 1 11 + 1 = 12 The new nucleus has an atomic number of 12 Step 3: Calculate the new mass number Protons and neutrons both have a mass number of 1 Changing a neutron to a proton will not affect the mass number The new nucleus has a mass number of 24 (the same as before) Page 27 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Detecting Radiation Your notes Detecting radiation Ionising radiation can be detected using photographic film a Geiger–Müller tube Photographic film Photographic films detect radiation by becoming darker when it absorbs radiation, similar to when it absorbs visible light The more radiation the film absorbs, the darker it is when it is developed People who work with radiation, such as radiographers, wear film badges which are checked regularly to monitor the levels of radiation absorbed To get an accurate measure of the dose received, the badge contains different materials that the radiation must penetrate to reach the film These materials may include aluminium, copper, paper, lead and plastic The diagram shows what a typical radiation badge looks like: A badge containing photographic film can be used to monitor a person’s exposure to radiation Geiger-Müller tube The Geiger-Müller tube is the most common device used to measure and detect radiation Each time it absorbs radiation, it transmits an electrical pulse to a counting machine This makes a clicking sound or displays the count rate The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Müller tube is absorbing Page 28 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Therefore, it matters how close the tube is to the radiation source The further away from the source, the lower the count rate detected Your notes A Geiger-Müller tube (or Geiger counter) is a common type of radiation detector Worked example A Geiger-Müller tube is used to detect radiation in a particular location. If it counts 16,000 decays in 1 hour, what is the count rate? Answer: Step 1: Identify the different variables The number of decays is 16 000 The time is 1 hour Step 2: Determine the time period in seconds 1 hour is equal to 60 minutes, and 1 minute is equal to 60 seconds Time period = 1 × 60 × 60 = 3600 seconds Step 3: Divide the total counts by the time period in seconds Counts ÷ Time period = 16 000 ÷ 3600 = 4.5 Therefore, it detects 4.5 decays per second Page 29 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes If asked to name a device for detecting radiation, the Geiger-Müller tube is a good example to give. You can also refer to it as a GM tube, a GM detector, GM counter, Geiger counter etc. (The examiners will allow some level of misspelling, providing it is readable). Don’t, however, refer to it as a ‘radiation detector’ as this is too vague and may simply restate what was asked for in the question. Page 30 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Background radiation It is important to remember that radiation is a natural phenomenon Your notes Radioactive elements have always existed on Earth and in outer space However, human activity has added to the amount of radiation that humans are exposed to on Earth Background radiation is defined as: The radiation that exists around us all the time Every second of the day there is some radiation emanating from natural sources such as: Rocks Cosmic rays from space Foods Chart of Background Radiation Sources Background radiation is the radiation that is present all around in the environment. Radon gas is given off from some types of rock There are two types of background radiation: Natural sources Artificial (man-made) sources Natural Sources of Background Radiation Page 31 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Radon gas from rocks and buildings Airborne radon gas comes from rocks in the ground, as well as building materials e.g. stone and brick Your notes This is due to the presence of radioactive elements, such as uranium, which occur naturally in small amounts in all rocks and soils Uranium decays into radon gas, which is an alpha emitter This is particularly dangerous if inhaled into the lungs in large quantities Radon gas is tasteless, colourless and odourless so it can only be detected using a Geiger counter Levels of radon gas are generally very low and are not a health concern, but they can vary significantly from place to place Cosmic rays from space The sun emits an enormous number of protons every second Some of these enter the Earth’s atmosphere at high speeds When they collide with molecules in the air, this leads to the production of gamma radiation Other sources of cosmic rays are supernovae and other high energy cosmic events Carbon-14 in biological material All organic matter contains a tiny amount of carbon-14 Living plants and animals constantly replace the supply of carbon in their systems hence the amount of carbon-14 in the system stays almost constant Radioactive material in food and drink Naturally occurring radioactive elements can get into food and water since they are in contact with rocks and soil containing these elements Some foods contain higher amounts such as potassium-40 in bananas However, the amount of radioactive material is minuscule and is not a cause for concern Artificial Sources of Background Radiation Nuclear medicine In medical settings, nuclear radiation is utilised all the time For example, X-rays, CT scans, radioactive tracers, and radiation therapy all use radiation Nuclear waste While nuclear waste itself does not contribute much to background radiation, it can be dangerous for the people handling it Nuclear fallout from nuclear weapons Fallout is the residue radioactive material that is thrown into the air after a nuclear explosion, such as the bomb that exploded at Hiroshima While the amount of fallout in the environment is presently very low, it would increase significantly in areas where nuclear weapons are tested Nuclear accidents Nuclear accidents, such as the incident at Chornobyl, contribute a large dose of radiation to the environment Page 32 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources While these accidents are now extremely rare, they can be catastrophic and render areas devastated for centuries Your notes Accounting for background radiation Background radiation must be accounted for when taking readings in a laboratory This can be done by taking readings with no radioactive source present and then subtracting this from readings with the source present This is known as the corrected count rate Measuring background count rate The background count rate can be measured using a Geiger-Müller (GM) tube with no source present For example, if a Geiger counter records 24 counts in 1 minute when no source is present, the background radiation count rate would be: 24 counts per minute (cpm) 24/60 = 0.4 counts per second (cps) Measuring the corrected count rate of a source The corrected count rate can be determined by measuring the count rate of a source and subtracting the background count rate Then, if the Geiger counter records, for example, 285 counts in 1 minute when a source is present, the corrected count rate would be: 285 − 24 = 261 counts per minute (cpm) Page 33 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 261/60 = 4.35 counts per second (cps) When measuring count rates, the accuracy of results can be improved by: Repeating readings and taking averages Your notes Taking readings over a long period of time Page 34 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes A student uses a Geiger counter to measure the counts per minute at different distances from a source of radiation. Their results and a graph of the results are shown below. Determine the background radiation count. Answer: Step 1: Determine the point at which the source radiation stops being detected The background radiation is the amount of radiation received all the time When the source is moved back far enough it is all absorbed by the air before reaching the Geiger counter Results after 1 metre do not change Therefore, the amount after 1 metre is only due to background radiation Step 2: State the background radiation count The background radiation count is 15 counts per minute Page 35 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes The sources that make the most significant contribution are the natural sources: Radon gas from rocks and buildings Food and drink Cosmic rays Make sure you remember these for your exam! 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