Comprehensive Notes on Radiation, Radioactivity, and Nuclear Technology

Discovery and Characteristics of Radioactivity

• In 1902, E. Rutherford was able to distinguish three distinct types of radiation based on three shared properties:
  • The origin of the radiation lies within the atomic nucleus.
  • Through the process of decay, the potential energy of the nucleus is reduced.
  • The decay occurs spontaneously.
• A primary identifier of the different types of radioactive radiation is their behavior in physical fields: $\gamma$-radiation, for instance, is not deflected.

Alpha (\alpha) Decay

• Definition and Mechanism:
  • Alpha decay is a nuclear transformation process.
  • It occurs because the nucleus is too heavy, making it inherently unstable.
  • The nucleus becomes more stable by emitting an alpha particle.
• Example Equation:
  • $^{238}_{92}\text{U} \rightarrow ^{234}_{90}\text{Th} + \alpha$
• Properties:
  • Range: It has a low range, measured in centimeters ($cm$).
  • Shielding: It is easily shielded or blocked by thin materials.
  • Biological Impact: It is characterized by very high harmfulness (a relative biological effect factor of $20$).

Beta (\beta) Decay

• Definition and Mechanism:
  • Beta decay is a nuclear transformation process occurring in two distinct forms: $\beta^-$-decay and $\beta^+$-decay.
  • In both cases, the nucleus possesses less energy after the decay occurs.
  • The energy decrease is attributed to the decaying nucleon jumping to a lower energy level.
• Properties:
  • Range: Approximately $10\,m$ in air.
  • Biological Impact: It has a relative harmfulness factor of $1$.

Gamma (\gamma) Radiation

• Definition and Mechanism:
  • This radiation occurs when an excited nucleon jumps to a lower energy level and emits a high-energy photon.
  • It is described as a "quantum jump in the nucleus."
• Properties:
  • Energy: Gamma radiation is the most energetic of all electromagnetic radiations.
  • Range: It has a very high range, extending for many kilometers ($km$).
  • Shielding: It can only be attenuated (weakened) but can never be completely shielded.
  • Biological Impact: It has a relative harmfulness factor of $1$.

Summary Table of Radioactive Radiation Types

• Alpha Radiation ($\alpha$):
  • Cause: Nucleus is too heavy.
  • General Formula: $^A_Z\text{X} \rightarrow ^{A-4}_{Z-2}\text{Y} + ^4_2\text{He}$
  • Example: $^{238}_{92}\text{U} \rightarrow ^{234}_{90}\text{Th} + \alpha$
  • Range in Air (m): $10^{-1}$
  • Range in Water (m): $10^{-4}$
  • Range in Lead (m): $10^{-5}$
  • Relative Biological Effect: $20$
• Beta-Minus Radiation ($\beta^-$):
  • Cause: Excess of neutrons.
  • General Formula: $^A_Z\text{X} \rightarrow ^{A}_{Z+1}\text{Y} + e^- + \overline{\nu}_e$
  • Example: $^{14}_{6}\text{C} \rightarrow ^{14}_{7}\text{N} + e^- + \overline{\nu}_e$
  • Range in Air (m): $10$
  • Range in Water (m): $10^{-3}$
  • Range in Lead (m): $10^{-4}$
  • Relative Biological Effect: $1$
• Beta-Plus Radiation ($\beta^+$):
  • Cause: Excess of protons.
  • General Formula: $^A_Z\text{X} \rightarrow ^{A}_{Z-1}\text{Y} + e^+ + \nu_e$
  • Example: $^{40}_{19}\text{K} \rightarrow ^{40}_{18}\text{Ar} + e^+ + \nu_e$
  • Range in Air (m): $10$
  • Range in Water (m): $10^{-3}$
  • Range in Lead (m): $10^{-4}$
  • Relative Biological Effect: $1$
• Gamma Radiation ($\gamma$):
  • Cause: Nucleus has too much energy.
  • General Formula: $^A_Z\text{X}^* \rightarrow ^A_Z\text{X} + \gamma$
  • Example: $^{60}_{28}\text{Ni}^* \rightarrow ^{60}_{28}\text{Ni} + \gamma$
  • Range in Air (m): $10^3$
  • Range in Water (m): $10^0$
  • Range in Lead (m): $10^{-1}$
  • Relative Biological Effect: $1$

Radiation Exposure and Safety Standards

• Exposure in Austria:
  • The average radiation exposure in Austria is approximately $4\,mSv$ (Millisievert) per year.
  • The largest contributor to this exposure is Radon. Approximately $15\%$ of all lung cancer deaths are attributed to this noble gas.
• Workplace Safety:
  • The legal limit for occupational exposure (e.g., for physicians or physicists) is set at $30\,mSv$ per year.
  • Exposure levels are monitored and measured using a device called a dosimeter.

Nuclear Energy: History and Fission Mechanics

• Historical Background:
  • Uranium is identified as the heaviest naturally occurring element.
  • In 1938, Otto Hahn and Fritz Strassmann attempted to create even heavier nuclei by bombarding Uranium with neutrons.
  • The experiment did not result in heavier elements; instead, new medium-heavy elements were created. This was explained by Lise Meitner and the researchers as the Uranium nuclei splitting into two parts due to neutron bombardment.
• Process of Nuclear Fission:
  • When a neutron strikes an isotope such as $^{235}\text{U}$, the nucleus becomes unstable and decays (splits).
  • Heavy nuclei use a large number of neutrons as "putty" (Kitt) to hold the core together. Medium-heavy nuclei resulting from fission require fewer neutrons.
  • Consequently, each fission event releases additional neutrons, which then hit other nuclei, leading to a self-sustaining chain reaction.

Nuclear Power Plant Operation and Risk Management

• Operational Principle:
  • Nuclear power plants are essentially thermal power plants.
  • The energy released during nuclear fission is used to generate steam. This steam drives a turbine, which in turn powers a generator to produce electricity.
• Risk Mitigation Strategies:
  • Ionizing Radiation: The reactor core is surrounded by meter-thick concrete walls to block radiation.
  • Leakage of Radioactive Material: Uranium fuel is welded into tubes. A secondary security container surrounds the fuel. The system is kept under negative pressure, and all exhaust air is filtered.
  • Power Control (Excessive Power): Control rods are used to manage the number of available neutrons. The process is managed by an automatic reactor control system.
  • Cooling System Failure: If the cooling system fails, the reactor is automatically shut down, and an emergency cooling system is activated.

Transport, Waste, and Global Scale

• Fuel Management:
  • Transport: Fuel elements are moved in heavily protected containers.
  • Reprocessing: Spaltable (fissile) material is recovered, and radioactive waste is prepared for final storage via irradiation.
• Final Disposal:
  • Radioactive waste (including air filters, water filters, and spent fuel elements) is solidified in bitumen and cast into steel drums.
  • These drums are stored in final repositories, such as decommissioned mines.
• Global Statistics:
  • As of 2007, there were $441$ nuclear power plants operating in $33$ countries worldwide.

Nuclear Fusion

• Basic Principle: Kernfusion (Nuclear fusion) involves merging light atomic nuclei into heavier ones, a process that releases massive amounts of energy.
• Natural Occurrence: In the Sun, fusion creates the light and heat necessary to sustain life on Earth.
• Technological Progress:
  • Realizing fusion on Earth requires extremely high temperatures and specialized facilities.
  • ITER: The ITER research reactor in France is a critical step toward fusion power. Based on the Tokamak principle, it is designed to generate a hydrogen plasma for the first time in 2025.

Nuclear Weapons

• Mechanism: The energy of nuclear weapons is derived from the chain reaction principle.
• Detonation Process:
  • Fissile material is initially arranged to be subcritical, meaning no spontaneous explosion occurs.
  • Conventional explosives are used to force subcritical masses together, making the mass supercritical and triggering an explosion.
• Effects:
  • Extreme temperatures exceeding $100 \times 10^6\,K$ ($100$ million Kelvin).
  • Extreme pressure waves.
  • Ionizing radiation and radioactive fallout that persists for years or even centuries.
• The Hydrogen Bomb (Thermonuclear Weapon):
  • An atomic (fission) bomb is used as an igniter.
  • The resulting heat and pressure trigger the fusion of Deuterium and Tritium nuclei contained in a separate tank.
  • The impact and destructive power are significantly greater than a standard atomic bomb.
• Global Context: There are currently approximately $13,000$ nuclear warheads in the world, a quantity sufficient to destroy the Earth countless times.