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Topic 5: Nuclear physics
Topic 5: Nuclear physics
Study guide
Study guide
Complete topic summary
Complete topic summary
1. The Atom:
Structure: Atoms consist of a nucleus containing protons (positive charge) and neutrons (no charge), surrounded by orbiting electrons (negative charge). "The nucleus is the dense center of an atom, made up of protons and neutrons."
Proton Number (Atomic Number, Z): Defines the element. "The Proton Number (often called the Atomic Number, Z) is the number of protons in the nucleus of an atom. This number defines the element"
Nucleon Number (Mass Number, A): The total number of protons and neutrons in the nucleus. "The Nucleon Number (or Mass Number, A) is the total number of protons and neutrons in the nucleus."
Neutron Calculation: Number of neutrons = A - Z. "To find the number of neutrons, you can use the formula: Number of neutrons = A − Z"
Nuclear Notation: A standardised way to represent an atom's composition. "Nuclear notation is a standardi s ed way to represent information about an atom." Example: Representation includes the chemical symbol, nucleon number (A), and proton number (Z).
2. Isotopes and Ions:
Isotopes: Atoms of the same element (same number of protons) but with different numbers of neutrons. " Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons." For example, Carbon-12 and Carbon-14. Isotopes have similar chemical properties but potentially different physical properties.
Ions: Atoms that have gained or lost electrons, resulting in a net electrical charge. "Atoms can gain or lose electrons to form ions, which are charged particles" Positive ions (cations) have lost electrons; negative ions (anions) have gained electrons.
3. Detection of Radioactivity & Background Radiation:
Background Radiation: Low-level ionising radiation that is always present in the environment from natural and man-made sources. "Background radiation is the low level of ionising radiation that is always present in the environment." Sources include radon gas, rocks and buildings, food and drink, and cosmic rays. "Radon is a naturally occurring radioactive gas that comes from the decay of uranium in the Earth's crust. It seeps out of the ground and accumulates in the air, particularly in buildings that are poorly ventilated."
Measuring Radiation: Ionising radiation is measured using a radiation detector connected to a counter, such as a Geiger-Müller (GM) tube. "Ionising radiation can be measured using a radiation detector connected to a counter."
Count Rate: The number of radioactive events detected per unit of time (e.g., counts per second or counts per minute). "The count rate is the number of radioactive events detected per second or minute."
4. Half-Life:
Definition: The time taken for half the nuclei of a radioactive isotope in a sample to decay. "The half-life of a radioactive isotope is defined as: The time taken for half the nuclei of that isotope in any sample to decay."
Calculation: Half-life can be calculated from data or decay curves (graphs showing the decline of radioactive material over time).
Background Radiation Considerations: Half-life calculations assume background radiation is not included in the initial measurements. "For calculations, it is assumed that background radiation is not included."
5. Types of Nuclear Emission (Radioactive Decay):
Radioactive Decay: The spontaneous and random process by which an unstable nucleus emits radiation to become more stable. "Radioactive decay is the process in which an unstable atomic nucleus emits radiation to become more stable."
Alpha (α) Radiation:Composed of 2 protons and 2 neutrons (Helium nucleus). "Composed of 2 protons and 2 neutrons."
Highly ionising. "Highly ionising due to its large mass and double positive charge."
Low penetration (stopped by paper or a few cm of air). "Low penetration. It can be stopped by a sheet of paper or a few centimeters of air."
Beta (β) Radiation:Beta-minus (β⁻) particles are electrons emitted from the nucleus. "Beta-minus (β⁻) particles are electrons emitted from the nucleus when a neutron decays into a proton."
Moderately ionising. "Moderately ionising."
Moderate penetration (stopped by a few mm of aluminium). "Moderate penetration. It can be stopped by a few millimeters of aluminium or other light metals."
Gamma (γ) Radiation:Electromagnetic wave (high-energy photons). "Electromagnetic wave with no mass and no charge."
Weakly ionising. "Weakly ionising."
High penetration (requires dense materials like lead or concrete for shielding). "High penetration. It can pass through several centimeters of lead or meters of concrete."
Nuclear Change During Decay: Alpha or Beta decay results in a change of element. "During alpha or beta decay, the nucleus changes to that of a different element."
6. Safety Precautions:
Effects of Ionising Radiation: Can cause cell death, mutations, and cancer. "Prolonged or high levels of radiation exposure can lead to cancer."
Safe Handling:Transportation: Radioactive materials are transported in specially designed containers made of thick lead or other shielding materials.
Usage: Remote tools and manipulators are used to maintain a safe distance.
Storage: Radioactive substances are stored in secure, lead-lined containers in designated areas. "Radioactive substances are stored in secure lead-lined containers to contain the radiation."
Shielding: The type and thickness of shielding depend on the type of radiation. Alpha can be stopped by paper, beta by aluminum, and gamma requires lead or concrete.
Example short answer questions
Example short answer questions
What is background radiation, and what are two common sources of it?
Background radiation is the low-level ionising radiation present in the environment at all times. Two common sources are radon gas from the ground and cosmic rays from space.
2. Explain how a Geiger-Müller tube is used to detect radiation and how the count rate is interpreted.
A Geiger-Müller tube detects radiation by sensing ionising particles, which then produce an electrical signal. The count rate, measured in counts per second or minute, indicates the amount of radiation present.
3. Define half-life, and explain what it signifies in the context of radioactive decay.
Half-life is the time it takes for half the nuclei of a radioactive isotope in a sample to decay. It signifies the rate at which a radioactive substance decays.
4. How do isotopes differ from one another, and what remains the same? Give an example.
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. For example, Carbon-12 and Carbon-14 are isotopes of carbon.
5. Describe three potential effects of ionising radiation on living things, and why they occur.
Ionising radiation can cause cell death by directly killing cells, mutations by altering DNA, and cancer by causing cells to divide uncontrollably. These effects result from the radiation's ability to knock electrons out of atoms, disrupting cellular processes.
6. What are some safety precautions taken when handling radioactive materials during transportation and storage?
Radioactive materials are transported in thick, lead-lined containers to prevent radiation leakage. Storage involves keeping substances in secure, lead-lined containers in designated areas with warning signs.
7. Describe the composition of an atom, including the location and properties of protons, neutrons, and electrons.
An atom consists of a nucleus containing protons (positive charge) and neutrons (no charge), surrounded by orbiting electrons (negative charge). Protons determine the element's identity, while neutrons and protons contribute to the atom's mass.
8. What are the nature, ionising effect, and penetrating abilities of alpha radiation?
Alpha radiation is composed of 2 protons and 2 neutrons (a helium nucleus), is highly ionising due to its large mass and charge, and has low penetrating ability, being stopped by paper or a few centimetres of air.
9. How does Beta decay change an unstable nucleus?
In Beta decay, a neutron in the nucleus is converted into a proton and an electron (beta particle), which is emitted from the nucleus. This results in an increase in the proton number by one, and a different element is formed.
10. What are isotopes and ions, and how do they differ from each other?
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons, leading to different nucleon numbers (mass numbers). For example, Carbon-12 and Carbon-14 are isotopes of carbon. They share similar chemical properties but may have different physical properties, such as different levels of radioactivity.
Ions, on the other hand, are formed when atoms gain or lose electrons, resulting in a net electrical charge. If an atom loses electrons, it forms a positive ion. If it gains electrons, it forms a negative ion. Ions of an element have differing chemical properties than their neutral atom counterpart.
11. What is background radiation, and what are its primary sources?
Background radiation refers to the low-level ionising radiation that is naturally present in the environment at all times. It originates from a combination of natural and man-made sources. Primary natural sources include radon gas (released from the Earth's crust), radioactive elements in rocks and buildings (like granite), trace amounts of radioactive elements in food and drink (such as potassium-40 in bananas), and cosmic rays from space. Man-made sources can include certain medical procedures and industrial processes, although natural sources tend to contribute more to overall exposure.
12. How is radioactivity detected and measured, and what is 'count rate'?
Radioactivity is detected using radiation detectors connected to a counter, a common example being the Geiger-Müller (GM) tube. The detector senses radiation, and the counter records the number of radioactive particles detected over a period of time.
The count rate is the number of radioactive events detected per unit of time, usually expressed in counts per second (counts/s) or counts per minute (counts/min). The count rate indicates the amount of radiation present in a particular area or the activity of a radioactive source.
13. What are the three main types of nuclear emission, and how do they differ in terms of nature, ionising effect, and penetrating ability?
The three main types of nuclear emission are alpha (α), beta (β), and gamma (γ) radiation.
Alpha (α) radiation: Consists of 2 protons and 2 neutrons (a helium nucleus), possessing a large mass and positive charge. It's highly ionising but has low penetration, being stopped by a sheet of paper or a few centimetres of air.
Beta (β) radiation: Consists of electrons (β⁻) emitted from the nucleus. It's lightweight and negatively charged. It has moderate ionising power and penetration, stopped by a few millimetres of aluminium.
Gamma (γ) radiation: Is a high-energy electromagnetic wave (photon) with no mass or charge. It's weakly ionising but has high penetration, requiring several centimetres of lead or meters of concrete for effective shielding.
14. What are the effects of ionising radiation on living things, and why is it important to handle radioactive materials safely?
Ionising radiation can cause several harmful effects on living things, including cell death (at high doses), mutations in DNA (potentially leading to genetic defects), and cancer (due to uncontrolled cell division). The severity of these effects depends on the type and amount of radiation exposure.
Due to these risks, it's crucial to handle radioactive materials safely. Safety measures include transporting materials in specially designed containers (often made of thick lead), using remote tools or manipulators to maintain a safe distance during usage, and storing materials in secure, lead-lined containers in designated storage areas with warning signs.
15. How does the number of protons and neutrons define an atom and its properties?
The number of protons in an atom's nucleus defines the element. All atoms with the same number of protons are considered to be the same element. This number is also called the atomic number (Z). The total number of protons and neutrons in the nucleus is known as the nucleon number or mass number (A). By subtracting the atomic number from the mass number (A - Z), you can determine the number of neutrons in the nucleus. While isotopes of an element can have different numbers of neutrons (affecting physical properties like radioactivity), they remain the same element due to the same number of protons. Changes to the number of protons can occur in alpha or beta decay and transforms the atom into a different element.
Key terms
Key terms
Atom: The basic building block of matter, consisting of protons, neutrons, and electrons.
Isotope: Atoms of the same element that have the same number of protons but different numbers of neutrons.
Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.
Radioactivity: The spontaneous emission of radiation from the nucleus of an unstable atom.
Alpha Radiation: A type of nuclear emission consisting of two protons and two neutrons (a helium nucleus).
Beta Radiation: A type of nuclear emission consisting of electrons or positrons.
Gamma Radiation: A type of nuclear emission consisting of high-energy electromagnetic waves.
Half-life: The time taken for half the nuclei of a radioactive isotope in a sample to decay.
Background Radiation: The low-level ionising radiation present in the environment from natural and man-made sources.
Count Rate: The number of radioactive events detected per unit of time, typically measured in counts per second (counts/s) or counts per minute (counts/min).
Proton Number (Atomic Number): The number of protons in the nucleus of an atom, which determines the element.
Nucleon Number (Mass Number): The total number of protons and neutrons in the nucleus of an atom.
Ionising Radiation: Radiation that has enough energy to remove electrons from atoms or molecules.
Geiger-Müller (GM) Tube: A device used to detect and measure ionising radiation.
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