Definition
Spontaneous process: Radioactive decay is a natural process that happens on its own without being started by anything outside. It occurs when the nucleus (center) of an unstable atom breaks down and gives off radiation so it can become more stable.
Random and uncontrollable: This process happens at unpredictable times. No one can say exactly when a single atom will decay, and we cannot stop it or speed it up by using machines or tools.
Unaffected by conditions: Radioactive decay is very special because it is not affected by outside changes like heat, cold, pressure, or chemical reactions. It keeps happening at the same rate no matter what the environment is like.
Types of Radioactive Decay
Alpha Decay
Alpha emission: In alpha decay, the nucleus of an atom becomes unstable and needs to get rid of some particles to become more stable. So, it releases a small, heavy particle called an alpha particle. This alpha particle is made up of 2 protons and 2 neutrons, which is exactly like the nucleus of a helium atom. That’s why scientists say an alpha particle is the same as a helium nucleus.
Nucleon loss: When the atom loses this alpha particle, it also loses 4 nucleons in total—nucleons are the particles inside the nucleus (protons and neutrons). Specifically, the atom gives up 2 protons and 2 neutrons.
Decrease in atomic numbers: Since the atom just lost 2 of its protons, its atomic number (which tells us what element it is) goes down by 2. And because it also lost 2 neutrons, its mass number (which is the total number of protons and neutrons) goes down by 4.
General alpha equation: Scientists show alpha decay using an equation like this: A/ZX → A-4/Z-2Y + ⁴₂He. This means an atom with mass number A and atomic number Z changes into a new atom (Y) with mass number A-4 and atomic number Z-2, plus an alpha particle.
Alpha example: A well-known example is Uranium-238, written as ²³⁸₉₂U. It undergoes alpha decay and turns into Thorium-234, written as ²³⁴₉₀Th, by giving off an alpha particle. The full equation looks like this: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He.
Beta Decay
Beta emission: In beta decay, the nucleus releases a beta particle, which is actually a very tiny and very fast-moving electron.
Neutron-to-proton conversion: Inside the nucleus, a neutron changes into a proton, and when this happens, it also gives off an electron (the beta particle), which shoots out of the atom.
Atomic number increase: Since the neutron became a proton, the atom now has one more proton, so the atomic number increases by 1. However, the mass number stays the same because a neutron and a proton both count as one nucleon.
General beta equation: The beta decay process is written like this: A/ZX → A/Z+1Y + ⁻¹₀e. This shows that the atom becomes a new element (Y) with one more proton and emits a beta particle.
Beta example: A common example is Carbon-14, written as ¹⁴₆C. It turns into Nitrogen-14 (¹⁴₇N) by giving off a beta particle. The equation looks like this: ¹⁴₆C → ¹⁴₇N + ⁻¹₀e.
Gamma Decay
Gamma emission: Gamma decay happens when the nucleus releases a burst of energy called a gamma ray. A gamma ray is a very strong and powerful energy wave, not a particle like alpha or beta particles.
Energy release only: During gamma decay, the nucleus doesn’t lose or gain any protons or neutrons. It just gives off extra energy, so the number of protons and neutrons stays exactly the same.
Gamma stability: The nucleus gives out gamma rays when it is in a high-energy state and wants to become more stable. Releasing this energy helps the nucleus settle down.
General gamma equation: The equation for gamma decay looks like this: A/ZX → A/ZX + γ*. The little star (*) means the nucleus had extra energy before it released the gamma ray.
Gamma example: An example of this is Cobalt-60, which gives off gamma rays to release energy and become more stable.
Radioactive Series
Decay sequence: Some radioactive atoms don’t become stable after just one decay. They need to go through a series of decays, step by step, until they finally turn into a stable atom.
Multiple decay types: This decay chain often includes both alpha decays and beta decays as the atom keeps changing and trying to reach stability.
Series example: A good example is Uranium-238. It goes through many changes, including both alpha and beta decays, until it finally becomes a stable atom called Lead-206.
Half-Life
Half-life definition: The half-life is the amount of time it takes for half of the radioactive atoms in a sample to change into something else (usually a different element or a stable form). If you start with 100 radioactive atoms, after one half-life, only 50 will still be radioactive—the other 50 will have decayed.
Unique property: Every type of radioactive substance (called a radioisotope) has its own special and fixed half-life. This number is different for each isotope and it does not change no matter what. Some half-lives are only seconds long, while others can last for millions of years.
Independence from conditions: The half-life stays the same even if the environment around it changes. This means whether the substance is hot, cold, under pressure, or kept in different chemical forms, the half-life does not get shorter or longer.
Decay progression: After each half-life, the number of radioactive atoms gets cut in half. So, after one half-life, half the atoms are left. After two half-lives, only a quarter of the original atoms remain. After three half-lives, only one-eighth is left, and so on.
Half-life formula:
N = (1/2)ⁿ × N₀
This formula helps you figure out how many radioactive atoms are left (N) after a certain number of half-lives (n). N₀ is how many atoms you started with.
Time relation:
n = t / T₁/₂
This formula tells you how many half-lives (n) have passed by dividing the total time (t) by the length of one half-life(T₁/₂).
Decay Curve
Graph of decay: A decay curve is a graph that shows how the number of radioactive atoms goes down over time. It helps us understand how fast or slow the atoms are decaying.
Undecayed nuclei: The curve shows the number of atoms that have not decayed yet (also called undecayed nuclei). As time goes on, this number keeps going down.
Halving behavior: The graph shows that after every half-life, the number of radioactive atoms is cut in half, following the same pattern as we explained earlier.
Exponential shape: The graph does not form a straight line. Instead, it has a curve that drops quickly at first and then slows down. This special kind of curve is called an exponential curve.
Applications of Radioisotopes
Medicine
Diagnostic tools: Doctors use radioactive substances called tracers to find out what’s happening inside the body. These tracers are injected or swallowed, and they travel through the body. Special cameras pick up the radiation they give off to show where the problem is, like a tumor or blocked organ.
Cancer treatment: Some types of radioactive materials are used to kill cancer cells. They give off strong radiation that can destroy cancer cells or make tumors smaller without surgery.
Industry
Thickness measurement: In factories, machines use radiation to measure how thick materials like paper, metal sheets, or plastic are while they’re being made. If the material is too thick or too thin, the machine can fix it automatically.
Flow tracking: Engineers add small amounts of radioactive material to liquids or gases inside pipes. The radiation helps them see how the fluid moves and find leaks or blockages in the system.
Archeology
Artifact dating: Scientists use radioactive materials to find out the age of ancient objects, like bones or tools. By measuring how much of the radioactive material is left, they can estimate how long ago the object was alive or used.
Carbon-14 dating: A special technique called carbon-14 dating is used to find out how old things are if they were once alive (like wood, cloth, or bone). Carbon-14 is a radioactive isotope found in all living things.
Other Uses
Sterilization: Radioactive rays can kill bacteria and germs, so they are used to clean food and medical tools without using heat or chemicals.
Liquid flow measurement: Scientists and engineers use radioisotopes to study how liquids move in big systems, like in water treatment plants or cooling systems.
Blood cell labeling: In labs, scientists attach tiny amounts of radioactive material to blood cells. They then track where the blood cells go in the body. This helps them study how the blood moves and diagnose problems.