Radioactivity and particles

### The Atomic Nucleus

At the centre of every atom is a nucleus, containing positively charged protons and neutral neutrons. These are collectively known as nucleons. The identity of an element is determined by its atomic number (Z), which is the number of protons. The mass number (A) is the total number of protons and neutrons in the nucleus.

Atoms of the same element can have different numbers of neutrons; these are called isotopes. For example, Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons) are isotopes of carbon. While chemically identical, their nuclear properties can differ significantly. Some isotopic nuclei are inherently unstable due to an imbalance in the forces holding the nucleus together.

### Radioactive Decay

To achieve stability, an unstable nucleus undergoes radioactive decay, a process where it spontaneously emits energy and/or particles. This emission is known as nuclear radiation. The process is both spontaneous (it happens without any external influence) and random (it is impossible to predict which specific nucleus will decay next).

There are three main types of nuclear radiation:

* Properties: It has a charge of +2e, is relatively large and slow-moving. It has very high ionising power (it easily knocks electrons off atoms it passes) but very low penetrating power (it can be stopped by a sheet of paper or a few centimetres of air).

* Alpha Decay Process: When a nucleus emits an alpha particle, its mass number (A) decreases by 4 and its atomic number (Z) decreases by 2.

^A_ZX → ^A-4_Z-2Y + ⁴₂He

* Properties: It has a charge of -1e. It has medium ionising and penetrating power, being stopped by a few millimetres of aluminium.

* Beta Decay Process: When a nucleus undergoes beta decay, its mass number (A) remains unchanged, but its atomic number (Z) increases by 1.

^A_ZX → ^A_Z+1Y + ⁰_-1e

* Properties: Gamma rays have no mass and no charge. They have very low ionising power but extremely high penetrating power, requiring several centimetres of lead or thick concrete to be significantly absorbed.

### Half-Life and Activity

The activity of a radioactive source is the rate at which its nuclei decay, measured in becquerels (Bq), where 1 Bq = 1 decay per second. The rate of decay decreases over time as the number of unstable nuclei reduces.

The half-life (T_1/2) is a crucial concept. It is defined as the average time taken for the number of undecayed nuclei in a sample to be reduced to half its original value, or equivalently, the time it takes for the activity of the sample to halve. Half-lives can range from fractions of a second to billions of years.

After 'n' half-lives, the remaining fraction of undecayed nuclei is (1/2)ⁿ.

### Detection and Safety

Nuclear radiation is invisible but can be detected using instruments like the Geiger-Müller (GM) tube. When radiation enters the tube, it ionises the gas inside, creating a short electrical pulse that can be counted, producing the familiar 'clicking' sound.

It's important to account for background radiation, which is the low-level radiation present in our environment from natural sources (like cosmic rays and radioactive rocks) and man-made sources (like medical procedures). A measurement of background count should be taken and subtracted from any readings to find the true activity of a source.

Because ionising radiation can damage living cells, strict safety precautions are necessary:

* Minimise exposure time.

* Maximise distance from the source.

* Use appropriate shielding (e.g., lead aprons, concrete walls).