Magnetism and magnetic fields Study Guide

Radioactive decay releases several types of radiation, each with distinct penetration properties. Understanding these differences is crucial for safety and for their applications. Alpha particles are relatively heavy and carry a positive charge. They interact strongly with matter, causing them to lose energy quickly. This means alpha particles have a very short range in air and can be stopped by a thin sheet of paper or even the outer layer of dead skin cells. Beta particles are much lighter and have a negative charge. They interact less strongly than alpha particles, allowing them to penetrate further. Beta radiation can travel several metres in air and requires a few millimetres of aluminium to be completely absorbed. Gamma rays are electromagnetic radiation, not particles. They have no mass or charge and interact very weakly with matter. This gives them the greatest penetrating power. Gamma rays can travel long distances in air and require thick layers of dense materials like lead or concrete to significantly reduce their intensity. These differences mean that the hazard posed by each radiation type depends on whether the source is inside or outside the body. Alpha emitters are very dangerous if ingested or inhaled, as their high ionising power can damage internal tissues. Outside the body, they pose less risk due to their low penetration. Conversely, gamma emitters are a significant external hazard due to their high penetration, but less dangerous internally per unit energy due to their low ionising power.

The electromagnetic spectrum is a continuous range of waves, all of which are transverse waves and travel at the speed of light in a vacuum. These waves vary in their properties, specifically their frequency and wavelength. Frequency is defined as the number of wave cycles passing a point per second, measured in Hertz (Hz). Wavelength is the distance between two consecutive identical points on a wave, such as two crests or two troughs, measured in metres (m). There is a fundamental relationship between frequency, wavelength, and the speed of a wave, expressed by the wave equation: wave speed (v) = frequency (f) × wavelength (λ). For all electromagnetic waves, their speed in a vacuum is constant, approximately 3 x 10^8 metres per second (m/s). This constant speed means that as the frequency of an electromagnetic wave increases, its wavelength must decrease proportionally, and vice versa. This inverse relationship is crucial for understanding the entire electromagnetic spectrum, from long-wavelength radio waves with low frequencies to short-wavelength gamma rays with very high frequencies. For example, radio waves have very long wavelengths, often hundreds of metres, and correspondingly low frequencies. Microwaves have shorter wavelengths than radio waves, and therefore higher frequencies. Visible light occupies a small portion of the spectrum, with different colours corresponding to different wavelengths and frequencies. Ultraviolet, X-rays, and gamma rays have progressively shorter wavelengths and higher frequencies. This relationship helps explain why different regions of the spectrum have different energy levels and uses. Higher frequency (shorter wavelength) waves carry more energy, which is why gamma rays and X-rays are ionising and can be harmful to living tissue, while radio waves are relatively harmless.