Atomic Structure

Think of atoms as incredibly tiny building blocks - so small that their radius is about 1 × 10⁻¹⁰ metres! Every atom has a positively charged nucleus at its centre, made up of protons and neutrons, with negatively charged electrons whizzing around it at different distances.

Here's what makes atoms fascinating: the nucleus is absolutely tiny compared to the whole atom $less than 1/10,000 of the atom's radius$, yet it contains almost all the atom's mass. The electrons hang out at different energy levels around the nucleus, and they can jump between these levels by absorbing or releasing electromagnetic radiation.

What keeps everything balanced? In any atom, the number of electrons always equals the number of protons, giving the atom no overall charge. The atomic number tells you how many protons an element has, while the mass number is the total of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons - same element, different mass!

Quick Tip: Remember that atoms become positive ions when they lose electrons - this is crucial for understanding chemical reactions!

Development of Atomic Models and Radioactive Decay

Scientists didn't always know what atoms looked like - our understanding evolved through brilliant experiments! We went from thinking atoms were solid spheres, to the plum pudding model (a ball of positive charge with electrons stuck in it), to the nuclear model after the famous gold foil experiment showed that atoms have dense, charged centres.

Niels Bohr then suggested electrons orbit at specific distances, and later scientists like James Chadwick discovered neutrons. Science keeps evolving as new evidence emerges!

Some atomic nuclei are unstable and undergo radioactive decay - a completely random process where they release radiation to become more stable. We measure this activity in becquerels (Bq), which tells us the decay rate.

There are three main types of nuclear radiation: Alpha particles $2 protons + 2 neutrons, stopped by paper$, Beta particles $high-speed electrons, stopped by aluminium$, and Gamma rays (electromagnetic radiation, needs lead to stop). Each has different penetrating power and ionising ability.

Remember: Alpha particles are the most ionising but least penetrating - they're dangerous inside your body but can't even get through paper!

Nuclear Equations and Half-Life

Nuclear equations help us track what happens during radioactive decay. When an atom releases an alpha particle, both its mass and charge decrease. Beta decay keeps the mass the same but increases the charge. Gamma rays don't change either - they just release energy.

The concept of half-life is absolutely crucial: it's the time needed for half the radioactive nuclei in a sample to decay, or for the count rate to drop to half its original value. While individual atoms decay randomly (you can't predict which one will go next!), large groups follow predictable statistical patterns.

Half-life calculations follow a simple pattern: after each half-life period, you're left with half of what you started with. So if you begin with 100g and the half-life is 10 years, you'll have 50g after 10 years, 25g after 20 years, and so on.

Pro Tip: Half-life problems are common exam questions - practice the formula N = N₀ × (1/2)ⁿ where n is the number of half-lives!

Radiation Hazards and Protection

Understanding radiation hazards could literally save your life! Radioactive contamination means unwanted radioactive material gets on or in other objects, while irradiation is simply being exposed to radiation without becoming radioactive yourself.

Protection strategies are straightforward: use the lowest activity sources for the shortest time possible, wear protective clothing like lead aprons, and never handle radioactive sources with bare hands. The type of radiation matters hugely - contaminated food with alpha sources is more dangerous than gamma contamination because alpha particles are more ionising when inside your body.

Background radiation is everywhere, coming from natural sources like cosmic rays and rocks, plus human activities like nuclear weapons testing. We measure radiation exposure in sieverts (Sv), with 1000 millisieverts equaling 1 sievert.

Half-life length affects hazard levels differently: short half-lives mean intense but brief danger, while long half-lives create prolonged, lower-level risks that can persist for decades.

Key Point: Alpha contamination inside your body is extremely dangerous, but gamma contamination nearby poses the greater external threat due to its penetrating power!

Medical Uses of Nuclear Radiation

Nuclear radiation isn't just dangerous - it's incredibly useful in medicine! Doctors use radioactive isotopes as tracers to explore internal organs by injecting or having patients ingest them, then detecting the radiation from outside the body.

For treatment, focused gamma ray beams can destroy tumours, while radioactive iodine specifically targets thyroid problems. Kidney function monitoring works brilliantly: if radioactive material builds up in one kidney but not the other, doctors know there's a problem.

Choosing the right isotope requires careful consideration of half-life, activity, and radiation type. You need a half-life long enough to get results but short enough that patients don't stay radioactive for ages. Gamma sources make the best medical tracers because they penetrate tissue easily and are the least ionising.

Intestinal blockages show up clearly when radioactive tracers can't pass through, or when they leak into areas where they shouldn't be. It's like having a radioactive GPS system inside your body!

Medical Insight: Gamma rays are perfect for medical imaging because they can escape the body to be detected, unlike alpha or beta particles which get absorbed!