Knowt
Radioactivity
Atomic Structure
Inside the Atom
The atom consists of a small, dense, positively charged nucleus surrounded by negatively charged electrons. The nucleus contains protons and neutrons.
Protons have a positive charge. Neutrons have no charge. Electrons have a negative charge.
The diameter of a nucleus is about 100,000 times smaller than the diameter of the whole atom. However, almost all the mass of an atom is in the nucleus.
Electrons exist in shells or energy levels at different distances from the nucleus. The inner shells are filled before the outer shells.
Subatomic Particles
Protons have a relative mass of 1 and a charge of +1. Found in the nucleus.
Neutrons have a relative mass of 1 and no charge. Found in the nucleus.
Electrons have a very small relative mass and a charge of -1. Found in electron shells.
Atomic Number and Mass Number
Each element has a unique atomic number (Z) equal to the number of protons in the nucleus. This defines the element.
The mass number (A) is the total number of protons and neutrons in the nucleus.
Isotopes of an element have the same atomic number but different mass numbers due to varying numbers of neutrons.
Electron Structure
The first shell can hold up to 2 electrons, the second up to 8, the third up to 8, and the fourth up to 18.
Electrons fill the lowest available energy levels first, following the Aufbau principle - which states that, in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy level before occupying higher energy levels.
Valence electrons in the outermost occupied shell determine chemical properties.
Ions
Atoms can gain or lose electrons to form ions with a net positive or negative charge.
Cations are positively charged ions formed when atoms lose electrons.
Anions are negatively charged ions formed when atoms gain electrons.
Radioactive Decay
Types of Radiation
There are 3 main types of radiation that are emitted during radioactive decay:
Alpha (α) particles - Made up of 2 protons and 2 neutrons. They have a +2 charge and are the least penetrating type of radiation. They can be stopped by a thin sheet of paper or the outer layer of human skin. Another property of alpha particles is that they are the same as a helium nucleus.
Beta negative (β) particles - Fast moving electrons ejected from the nucleus during decay. They have a -1 charge and can pass through a few millimetres of aluminium but can be stopped by the thickness of a hand. A beta particle is essentially be seen as an electron emitted from the nucleus during radioactive decay.
Gamma (γ) rays - High frequency electromagnetic waves emitted from the nucleus. They have no charge and are the most penetrating type of radiation. They can pass through several centimetres of lead but can be stopped by a thick concrete wall. Gamma rays are a form of electromagnetic radiation emitted from the atomic nucleus.
Radiation Properties
Ionizing radiation can remove electrons from atoms, causing cell damage.
Alpha particles have very short range but high ionising power.
Beta particles can travel further and have medium ionising power.
Gamma rays have long range and low ionising power but are penetrative.
Radioactive Decay
Radioactive decay is the process where an unstable nucleus spontaneously emits radiation and transforms into a more stable nucleus. There are several types of radioactive decay:
Alpha Decay - The nucleus emits an alpha particle, reducing the atomic number by 2 and the mass number by 4. For example:
238U → 234Th + 4He
Beta Decay - A neutron in the nucleus is converted into a proton, electron, and neutrino. The atomic number increases by 1 while the mass number stays the same. For example:
214Bi → 214Po + e- + ν
Gamma Decay - The nucleus emits a gamma ray photon, losing energy but without any change to the composition of the nucleus. Gamma decay often follows alpha or beta decay.
Positron Decay - A proton is converted into a neutron, positron, and neutrino. The atomic number decreases by 1 while the mass number stays the same.
Measuring Radioactivity
These are 2 methods for measuring and detecting radioactivity:
Photographic Film:
Photographic film operates on the principle of ionization in its emulsion. When exposed to radiation, ionization occurs, leading to chemical changes in the film. Darkened areas on the film indicate the intensity and type of radiation exposure. This method is commonly employed in dosimetry and environmental monitoring.
Geiger–Müller Tube:
The Geiger–Müller tube detects ionizing radiation by measuring electrical charge produced during ionization events. As radiation enters the tube, ionization of the gas inside generates an electric pulse. This pulse is amplified and counted, providing information on radiation intensity. Geiger–Müller tubes are widely used in laboratories and environmental monitoring to detect and measure alpha, beta, and gamma radiation.
Half-Life
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or for the rate of decay to halve.
Short half-life isotopes decay more rapidly, while long half-life isotopes decay slowly over longer periods.
The activity of a radioactive sample decreases over time as more nuclei decay. The time for the activity to halve is the same as the half-life.
Uses of Radioactive Materials
Medicine - Radiotracers used in imaging scans (PET and SPECT), radiation therapy for cancer treatment.
Industry - Thickness and density gauges, radiography to check for cracks and faults.
Agriculture - Sterilisation of food, and tracers to monitor processes in plants.
Archaeology - Carbon dating to determine the age of ancient artifacts.
Power generation - Nuclear fission reactors, radioisotope thermoelectric generators.
Dangers and Control of Radiation
Biological Effects
Ionising radiation can damage cells and cause mutations that may lead to cancer.
Contamination from radioactive sources must be carefully controlled and disposed of.
Exposure to radiation should be kept as low as reasonably achievable.
Cumulative exposure increases lifetime risk.
Exposure Limits
Time - Minimise exposure time.
Distance - Maximize distance from source.
Shielding - Use lead, concrete, and water to absorb radiation.
Monitoring - Use Geiger counters and dosimeters.
Protectiveequipment - Lab coat, gloves, safety goggles.
Proper handling, storage and disposal of radioactive waste is vital. Nuclear waste is buried deep underground.
Nuclear Fission and Fusion
Nuclear Fission
Heavy nuclei like uranium-235 can split into lighter nuclei when hit by a neutron.
Fission releases energy and more neutrons that can cause further splitting.
This chain reaction is controlled in nuclear reactors to produce energy.
Nuclear Fusion
Fusion joins together light nuclei to make heavier ones, releasing energy.
Occurs naturally in stars where high temperatures overcome electrostatic repulsion.
Extreme conditions are needed to achieve controlled fusion for energy production.
Nuclear equations
Nuclear radioactive decay equations provide insights into the alterations in mass and charge within decaying nuclei. Each term in these equations is designated by the chemical symbol of the element or the type of radiation involved.
Nuclear Notation
The upper number, A, signifies the nucleon number or mass number, representing the total count of protons and neutrons in the nucleus. The lower number, Z, denotes the proton or atomic number, indicating the total count of protons in the nucleus.
AZ X
A : nucleon number
Z : prison number
X : chemical symbol for the elemenr
Balancing Nuclear Equations
Similar to chemical equations, nuclear equations must be balanced. This entails ensuring that the sum of the nucleon numbers on the left equals the sum on the right, and the sum of the proton numbers is balanced on both sides.
Alpha Decay Equation
For alpha decay, the nucleon number of the daughter nucleus is 4 less than that of the parent, and the proton number is 2 less.
AZ X —> A-4Z-2 Y + 42 Alpha particle
the mass number decreases by 4
the atomic number decreases by 2
Beta Minus Decay Equation
In beta minus decay, the nucleon number of the daughter nucleus remains the same as the parent, while the proton number increases by 1.
AZ X —> AZ+1 Y + B0-1 Beta particle
the mass stays the same
the atomic number increases by 1
Beta Plus Decay Equation
For beta plus decay, the nucleon number of the daughter nucleus matches the parent, but the proton number decreases by 1.
AZ X —> AZ-1 Y + B0+1 Beta particle
the mass stays the same
the atomic number decreases by 1
Gamma Decay Equation
In gamma decay equations, both the nucleon and proton numbers of the daughter nucleus remain the same as the parent.
AZ X —> AZ X + G00 Gamma particle
Radioactivity
Atomic Structure
Inside the Atom
The atom consists of a small, dense, positively charged nucleus surrounded by negatively charged electrons. The nucleus contains protons and neutrons.
Protons have a positive charge. Neutrons have no charge. Electrons have a negative charge.
The diameter of a nucleus is about 100,000 times smaller than the diameter of the whole atom. However, almost all the mass of an atom is in the nucleus.
Electrons exist in shells or energy levels at different distances from the nucleus. The inner shells are filled before the outer shells.
Subatomic Particles
Protons have a relative mass of 1 and a charge of +1. Found in the nucleus.
Neutrons have a relative mass of 1 and no charge. Found in the nucleus.
Electrons have a very small relative mass and a charge of -1. Found in electron shells.
Atomic Number and Mass Number
Each element has a unique atomic number (Z) equal to the number of protons in the nucleus. This defines the element.
The mass number (A) is the total number of protons and neutrons in the nucleus.
Isotopes of an element have the same atomic number but different mass numbers due to varying numbers of neutrons.
Electron Structure
The first shell can hold up to 2 electrons, the second up to 8, the third up to 8, and the fourth up to 18.
Electrons fill the lowest available energy levels first, following the Aufbau principle - which states that, in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy level before occupying higher energy levels.
Valence electrons in the outermost occupied shell determine chemical properties.
Ions
Atoms can gain or lose electrons to form ions with a net positive or negative charge.
Cations are positively charged ions formed when atoms lose electrons.
Anions are negatively charged ions formed when atoms gain electrons.
Radioactive Decay
Types of Radiation
There are 3 main types of radiation that are emitted during radioactive decay:
Alpha (α) particles - Made up of 2 protons and 2 neutrons. They have a +2 charge and are the least penetrating type of radiation. They can be stopped by a thin sheet of paper or the outer layer of human skin. Another property of alpha particles is that they are the same as a helium nucleus.
Beta negative (β) particles - Fast moving electrons ejected from the nucleus during decay. They have a -1 charge and can pass through a few millimetres of aluminium but can be stopped by the thickness of a hand. A beta particle is essentially be seen as an electron emitted from the nucleus during radioactive decay.
Gamma (γ) rays - High frequency electromagnetic waves emitted from the nucleus. They have no charge and are the most penetrating type of radiation. They can pass through several centimetres of lead but can be stopped by a thick concrete wall. Gamma rays are a form of electromagnetic radiation emitted from the atomic nucleus.
Radiation Properties
Ionizing radiation can remove electrons from atoms, causing cell damage.
Alpha particles have very short range but high ionising power.
Beta particles can travel further and have medium ionising power.
Gamma rays have long range and low ionising power but are penetrative.
Radioactive Decay
Radioactive decay is the process where an unstable nucleus spontaneously emits radiation and transforms into a more stable nucleus. There are several types of radioactive decay:
Alpha Decay - The nucleus emits an alpha particle, reducing the atomic number by 2 and the mass number by 4. For example:
238U → 234Th + 4He
Beta Decay - A neutron in the nucleus is converted into a proton, electron, and neutrino. The atomic number increases by 1 while the mass number stays the same. For example:
214Bi → 214Po + e- + ν
Gamma Decay - The nucleus emits a gamma ray photon, losing energy but without any change to the composition of the nucleus. Gamma decay often follows alpha or beta decay.
Positron Decay - A proton is converted into a neutron, positron, and neutrino. The atomic number decreases by 1 while the mass number stays the same.
Measuring Radioactivity
These are 2 methods for measuring and detecting radioactivity:
Photographic Film:
Photographic film operates on the principle of ionization in its emulsion. When exposed to radiation, ionization occurs, leading to chemical changes in the film. Darkened areas on the film indicate the intensity and type of radiation exposure. This method is commonly employed in dosimetry and environmental monitoring.
Geiger–Müller Tube:
The Geiger–Müller tube detects ionizing radiation by measuring electrical charge produced during ionization events. As radiation enters the tube, ionization of the gas inside generates an electric pulse. This pulse is amplified and counted, providing information on radiation intensity. Geiger–Müller tubes are widely used in laboratories and environmental monitoring to detect and measure alpha, beta, and gamma radiation.
Half-Life
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or for the rate of decay to halve.
Short half-life isotopes decay more rapidly, while long half-life isotopes decay slowly over longer periods.
The activity of a radioactive sample decreases over time as more nuclei decay. The time for the activity to halve is the same as the half-life.
Uses of Radioactive Materials
Medicine - Radiotracers used in imaging scans (PET and SPECT), radiation therapy for cancer treatment.
Industry - Thickness and density gauges, radiography to check for cracks and faults.
Agriculture - Sterilisation of food, and tracers to monitor processes in plants.
Archaeology - Carbon dating to determine the age of ancient artifacts.
Power generation - Nuclear fission reactors, radioisotope thermoelectric generators.
Dangers and Control of Radiation
Biological Effects
Ionising radiation can damage cells and cause mutations that may lead to cancer.
Contamination from radioactive sources must be carefully controlled and disposed of.
Exposure to radiation should be kept as low as reasonably achievable.
Cumulative exposure increases lifetime risk.
Exposure Limits
Time - Minimise exposure time.
Distance - Maximize distance from source.
Shielding - Use lead, concrete, and water to absorb radiation.
Monitoring - Use Geiger counters and dosimeters.
Protectiveequipment - Lab coat, gloves, safety goggles.
Proper handling, storage and disposal of radioactive waste is vital. Nuclear waste is buried deep underground.
Nuclear Fission and Fusion
Nuclear Fission
Heavy nuclei like uranium-235 can split into lighter nuclei when hit by a neutron.
Fission releases energy and more neutrons that can cause further splitting.
This chain reaction is controlled in nuclear reactors to produce energy.
Nuclear Fusion
Fusion joins together light nuclei to make heavier ones, releasing energy.
Occurs naturally in stars where high temperatures overcome electrostatic repulsion.
Extreme conditions are needed to achieve controlled fusion for energy production.
Nuclear equations
Nuclear radioactive decay equations provide insights into the alterations in mass and charge within decaying nuclei. Each term in these equations is designated by the chemical symbol of the element or the type of radiation involved.
Nuclear Notation
The upper number, A, signifies the nucleon number or mass number, representing the total count of protons and neutrons in the nucleus. The lower number, Z, denotes the proton or atomic number, indicating the total count of protons in the nucleus.
AZ X
A : nucleon number
Z : prison number
X : chemical symbol for the elemenr
Balancing Nuclear Equations
Similar to chemical equations, nuclear equations must be balanced. This entails ensuring that the sum of the nucleon numbers on the left equals the sum on the right, and the sum of the proton numbers is balanced on both sides.
Alpha Decay Equation
For alpha decay, the nucleon number of the daughter nucleus is 4 less than that of the parent, and the proton number is 2 less.
AZ X —> A-4Z-2 Y + 42 Alpha particle
the mass number decreases by 4
the atomic number decreases by 2
Beta Minus Decay Equation
In beta minus decay, the nucleon number of the daughter nucleus remains the same as the parent, while the proton number increases by 1.
AZ X —> AZ+1 Y + B0-1 Beta particle
the mass stays the same
the atomic number increases by 1
Beta Plus Decay Equation
For beta plus decay, the nucleon number of the daughter nucleus matches the parent, but the proton number decreases by 1.
AZ X —> AZ-1 Y + B0+1 Beta particle
the mass stays the same
the atomic number decreases by 1
Gamma Decay Equation
In gamma decay equations, both the nucleon and proton numbers of the daughter nucleus remain the same as the parent.
AZ X —> AZ X + G00 Gamma particle
