Fig. 46.1 shows the paths of three types of radiation passing between two charged plates. The table below summarises the properties of the three types of ra...

(a) Completing the six missing table entries

The six entries that were missing are shown in bold above. [1] for alpha = helium nucleus; [1] for gamma = electromagnetic wave; [1] for beta charge = -1 and beta stopped by aluminium.

(b) Why alpha curves toward the negative plate and beta toward the positive plate

• Alpha particles carry a positive charge (+2). In the electric field between the plates, they experience a force toward the negatively charged plate (opposite charges attract). [1]
• This force deflects the alpha path upward toward the negative plate. [1]
• Beta particles carry a negative charge (-1), so they are attracted toward the positive plate, curving their path downward. [1]

Gamma radiation has no charge (it is an electromagnetic wave), so it passes straight through the electric field without deflection.

(c) One practical use for each type of radiation

• Alpha: used in smoke alarms. The alpha particles ionise air in the detector; smoke disrupts this, triggering the alarm. [1]
• Beta: used in thickness monitoring in industry (e.g. paper or metal sheet manufacture). A beta source and detector are placed either side of the material; changes in detected count rate indicate thickness variation. [1]
• Gamma: used for sterilising medical equipment or as a medical tracer for imaging inside the body. Its high penetrating power makes it suitable for both applications. [1]