Radiation may seem frightening, but it naturally exists in the world and is widely used in medicine and industry. Let us understand it correctly.
Basic Knowledge
Radiation: A general term for high-energy particles and electromagnetic waves.
Main types:
① α (alpha) rays: Helium nuclei. Weak penetrating power (stopped even by paper), but strong ionizing power.
② β (beta) rays: Electrons. Medium penetrating power (stopped by a thin aluminum plate).
③ γ (gamma) rays: Electromagnetic waves. Strong penetrating power (weakened by lead・thick concrete).
④ X-rays: The same type of electromagnetic wave as γ rays, but produced differently. Used for X-ray examinations.
⑤ Neutron radiation: A flow of neutrons. Among the strongest in penetrating power.
Radiation (a flow like rays), radioactivity (the ability to emit radiation), and radioactive substances (substances that emit radiation) are different concepts.
Units of dose:
・Becquerel (Bq): The strength of radioactivity (the number of nuclei that decay in one second)
・Sievert (Sv): The magnitude of the effect on the human body
Radiation (High-energy particles・electromagnetic waves. α・β・γ・X・and neutron radiation)
Radioactivity (The ability to emit radiation. Refers to a property and amount)
Radioactive substance (A substance that emits radiation. Uranium・cesium・potassium, and so on)
Half-life (The time required for the amount of a radioactive substance to decrease by half)
Becquerel (Bq) (Unit of radioactivity. Number of decays per second)
Sievert (Sv) (Unit of effects on the human body)
In Depth (Background・Significance)
Radiation normally exists in nature, including cosmic rays, uranium・potassium in the Earth's crust, and radon in the air. The amount of natural radiation received by Japanese people is about 2.1 mSv per year.
Uses of radiation:
・Medicine: X-rays・CT (X-rays), PET examinations, and radiation therapy for cancer
・Industry: Nondestructive testing (welding defects in pipes), thickness gauges, and sterilization
・Agriculture: Pest control (sterilizing pests with radiation) and selective breeding
・Archaeology: Radiocarbon (C14) dating
・Power generation: Nuclear power generation (nuclear fission of uranium-235)
Risks of radiation: Large doses can damage DNA, cause cell death, and cause cancer. Safety management is important.
Half-life: The time required for the amount of a radioactive substance to decrease by half.
・Iodine-131: About 8 days
・Cesium-137: About 30 years
・Carbon-14: About 5730 years
・Uranium-238: About 45億 years
Measures against cesium-137 have become a long-term issue, particularly after the Fukushima Daiichi nuclear power plant accident.
- Radiation: α・β・γ・X・and neutron radiation
- Penetrating power: α<β<γ・X
- Radiation・radioactivity・and radioactive substances are different concepts
- Bq = strength of radioactivity, Sv = effects on the human body
- Natural radiation: about 2.1 mSv per year (Japanese average)
- Applications: medical diagnosis・cancer treatment・dating・and sterilization
- Half-life: iodine-131 about 8 days, cesium-137 about 30 years
Points to Note (Easily Confused)
① Strictly distinguish radiation (rays), radioactivity (ability), and radioactive substances (substances). “Radiation leak” is a colloquial expression; more precisely, it is a radioactive-substance leak. ② α rays are shielded by paper, β rays by aluminum, and γ rays by lead・concrete. ③ Bq indicates the activity of a substance, whereas Sv indicates effects on the human body. ④ Radiation also exists in nature and is not always artificial. Bananas also contain a small amount.
Practice
- Which has the strongest penetrating power among α・β・and γ rays?
- What is the unit of radioactivity?
- About how many years is the half-life of cesium-137?