Physics Unit 4 Radioactivity PDF

# Unit (4) Radioactivity ## Study Sheet ### Subject: Physics ### Grade: 9 ### Date: ### Block: 4 ### Week: ### Unit/Lesson/Topic: U(4) Radioactivity ### Objectives: - Recall from chemistry the structure of an atom in terms of protons, neutrons and electrons. - Identify the meaning of ion...

# Unit (4) Radioactivity ## Study Sheet ### Subject: Physics ### Grade: 9 ### Date: ### Block: 4 ### Week: ### Unit/Lesson/Topic: U(4) Radioactivity ### Objectives: - Recall from chemistry the structure of an atom in terms of protons, neutrons and electrons. - Identify the meaning of ionization. ## Unit (4) Radioactivity - The atom is the smallest unit of an element that maintains the chemical identity of that element. - Atoms are composed of particles called protons, neutrons, and electrons. - These particles are called subatomic particles. - Protons and neutrons are found in a small positively charged center of the atom called the nucleus that is surrounded by a cloud containing electrons. - Protons are particles with an electrical charge of 1+. - Electrons are particles with an electrical charge of 1-. - Neutrons are neutral particles that do not have an electrical charge. - Atoms are not charged even though they are made of charged protons and electrons. Neutral atoms have an equal number of protons and electrons whose charges cancel. **Example:** A lithium atom has 3 protons and 3 electrons. | Charge of | | | ---------- | -- | | 3 protons | +3 | | 3 neutrons | 0 | | 3 electrons | -3 | | Total charge | 0 | ### A: Mass number (nucleon number) (protons +neutrons). ### Z: Atomic number (proton number). ### Electron number= proton number. ### Neutron number= nucleon number - proton number (A-Z). ## What is the difference and similarities between these atoms? Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. ## Ionization In a neutral atom, the positive charges = negative charges. Ionization occurs when an atom loses or gains electrons, to be converted into positive or negative ions. **Positive ion:** when an atom loses electrons (positive charges > negative charges) **Negative ion:** when an atom gains electrons (negative charges > positive charges) ## Study Sheet ### Subject: Physics ### Grade: 9 ### Date: ### Block: 4 ### Week: ### Unit/Lesson/Topic: U(4) Radioactivity ### Objectives: - Identify the term of isotope Relate isotopes to their element. - Explain why some isotopes are radioactive. - Compare isotopes of hydrogen. - Interpret simple nuclear equations. - State that many elements have several isotopes, they are mostly non-radioactive (stable) but a few are radioactive. (eg., potassium (K-40) but it is only about 0.01% of natural potassium). ## Radioactive emission (decay): spontaneous random process in which unstable nuclei emit particles or waves to become stable, there are three types of emission, α, β, γ. ## Radioactivity of unstable nuclei: happens because these nuclei are too heavy (contain too many neutrons) so admit radiation to become more stable. ## Random process: This means we don't know which atom will decay next time, and don’t know in which direction next emission will be. Alpha and beta are particles, but gamma is electromagnetic waves. ## Isotopes It is a Greek word means the same place. Some elements have 36 isotopes. They are atoms of the same element with the same chemical properties and have the same number of protons but different numbers of neutrons. **Examples:** **Hydrogen** | | | | | ------------ | -- | --------- | | Protium | 1H | 1 proton | | Deuterium | 2H | 1 proton, 1 neutron | | Tritium | 3H | 1 proton, 2 neutrons | **Carbon** | | | | | | --------- | ------------- | -------------- | -------------- | | 12C | 12 Carbon | 6 protons, 8 neutrons | Carbon-12 | | 13C | 13 Carbon | 6 protons, 7 neutrons | Carbon-13 | | 14C | 14 Carbon | 6 protons, 8 neutrons | Carbon-14 | ## Stable and unstable nucleus of isotopes: | | | | | -------------- | ------------------------------ | ---------------------------------------- | | Stable nucleus | Balanced protons and neutrons. | Heavy as it has more neutrons. | | | Positive= negative | Unstable (change or decay randomly to be stable). | | | Remain stable (unchanged) | | ## Radioactive isotopes: an isotope having unstable nucleus that decomposes spontaneously Many (but not all) other elements have several isotopes. For naturally occurring materials, they are mostly non-radioactive (stable) but a few are radioactive. The most important example is potassium (K-40) but it is only about 0.01% of natural potassium ## Study Sheet ### Subject: Physics ### Grade: 9 ### Date: ### Block: 4 ### Week: ### Unit/Lesson/Topic: U(4) Radioactivity ### Objectives: - Describe the nature of alpha (α) particles, beta (β-) particles and gamma (γ) rays. - State the properties of alpha, beta, gamma decay. - Distinguish between alpha, beta and gamma. In terms of their structure, charge, penetration in air, and penetration through a variety of materials, deflection by electric field. ## 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 change - The mass number decreases by 4 - The atomic number decreases by 2 - The charge on the nucleus also decreases by 2 - This is because protons have a charge of +1 each. - An alpha particle can also be written as a helium nucleus (Symbol He) **e.g.** A X A-4 Z-2 Y 4 α 84 212Po 208 82 Pb 4 2 The polonium nucleus emits an alpha particle, causing its mass and charge to decrease. This means it changes into a new element. ## Beta Decay 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 new nuclei will increase its atomic number by 1 in order to maintain the overall atomic number before and after the decay 14C 14N -1 e- 6 7 0 - The carbon nucleus emits a beta particle, causing its charge to increase. This means it changes into a new element. ## Gamma Decay - During gamma decay, a gamma ray is emitted from an unstable nucleus - The process that makes the nucleus less energetic but does not change its structure 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. - Here is an example of Uranium-238 undergoing gamma decay - Notice that the mass number and atomic number of the unstable nuclei remains the same during the decay 238U 238U γ 92 92 Although the Uranium nucleus is unchanged in structure, its energy reduces during gamma decay ## properties of alpha, beta and gamma | Symbol | Penetrating power | Ionising power | Range in air | | -------- | ------------------------ | ---------------- | ------------ | | Alpha | Skin/paper | High | < 5 cm | | Beta | 3 mm aluminium foil | Low | ≈ 1 m | | Gamma | Lead/concrete | Very low | > 1 km | All types of radioactive decay can be detected by a Geiger-Muller tube or G-M tube. The radiations ionize the gas inside and the resulting charged particles move across the chamber and get counted as charges rather like an ammeter. ## Ionization (damage) - **Alpha (α):** - Strong - Slowest speed so more time for collision and interaction, - Largest charge. - Largest mass. - **Beta (β):** - Weak - Faster than alpha, more likely to pass straight without interaction. - Smaller charge. - Smaller mass.. - **Gamma (γ):** - Very weak - Fastest one. - No charge. - No mass. ## Deflection in electric field | | Alpha | Beta | Gamma | | ------------ | ---------- | ----------- | -------- | | Deflection in | Towards | Towards | Not Deflected | | electric field | negative plate. | positive plate. | (No Charge) | | | Weak deflection. | Strong deflection. | Straight line | | | Long curve. | Short curve. | | ## U(4) Radioactivity ### Study Sheet ### Subject: Physics ### Grade: 9 ### Date: ### Block: 4 ### Week: ### Unit/Lesson/Topic: U(4) Radioactivity ### Objectives: - State one medical one industrial use of radioactive isotopes - Relate each use of radiation to its property that make it suitable for this use - Explain why certain type of radiation is suitable for specific use while other type can't. ## Uses of Radiation Radiation is used in a number of different ways, for example: 1. Producing electricity through nuclear fission (Ur 235) 2. Checking the thickness of materials (Beta Particle) 3. Smoke detectors (Alpha particle) 4. Checking welding of metals (Gamma radiation) 5. Paper making (Beta particle) 6. Sterilization of medical tools (Gamma radiation) 7. Medical procedures including diagnosis and treatment (Beta particle) 8. Medical tracer (imaging) using technetium 99m (Gamma radiation) The properties of the different types of radiation determine which one is used in a particular application. ## Nuclear Power Stations Heat from the nuclear reaction is used to change water into steam in the boiler. The steam drives the turbine (heat to kinetic energy – the same as a conventional power station). This drives the generator to produce electricity - kinetic to electrical energy. ## **Uses of ALPHA particles** Used in smoke detectors (property - alpha particles ionize the air in the detector) Smoke alarms contain a weak source of alpha radiation. The alpha particles ionize the air. If there is smoke present, it interacts with the ions produced by the alpha particles and ionization is reduced. This means that less current is flowing through the air, which causes the alarm to sound. ## Uses of Beta particles - Prevents the build-up of static charges in paper-making, which could lead to dusty/dirty paper and/or fires. - Used in radiotherapy to weaken or damage cells, especially cancer cells (property – ionizing but with low penetration, so it can be focused on cancerous cells). - Used in Thickness gauge - Check thickness of materials/Use beta ray - If too thin, more beta particle penetrates through and the count rate increase - If too thick, less beta particle penetrates through and the count rate decrease ## Uses of Gamma waves - Produces pictures of welds to check for quality. - Sterilization of medical equipment (property – penetrating and ionising power of gamma radiation). - Medical imaging using technetium 99m (property – only emits gamma so there is little absorption and damage). Gamma rays can also be used to detect cracks after an object has been welded. Gamma rays are like X-rays. If a gamma source is placed on one side of the welded metal, and a photographic film on the other side, any flaws will show up on the film like an X-ray. ## Safety and radioactive sources Radiation can cause harm to living things, but the dangers can be minimized if the correct precautions are taken. 1. The time of exposure to ionising radiation should be limited. 2. Sources should be shielded from the body. 3. Sources should be stored in lead-lined containers to ensure no exposure to the environment whilst in storage. 4. Use lead apron and lead gloves when dealing with radioactive resources. 5. The radiation that a person receives can be monitored using film badges. 6. All areas containing ionising radiation sources will the show the hazard symbol.