10. (i) What is meant by radioactivity? In an experiment, the radiation from a radioactive source is passed through an electric field, as shown in the diagram - Leaving Cert Physics - Question 10 - 2014

This experiment illustrates that there are three distinct types of radiation: positive, negative, and neutral. The behavior of the radiation in the presence of an electric field helps identify its charge. If the radiation is deflected towards the positively charged plate, it is negatively charged; if it goes towards the negatively charged plate, it is positively charged; and if it is not deflected, it is neutral.

1. Gamma (γ)
2. Alpha (α)
3. Beta (β)

2 / gamma / γ

1 / alpha / α

3 / beta / β

1. Alpha (α)
2. Beta (β)
3. Gamma (γ)

Uranium-235 (U-235) or Plutonium-239 (Pu-239) are suitable fuels for nuclear fission.

Neutrons play a critical role in nuclear fission by initiating the fission process. When a neutron collides with a fissile nucleus (such as U-235), it can cause the nucleus to become unstable and split into smaller nuclei, releasing a significant amount of energy along with additional neutrons that can trigger further fission reactions.

Control rods are made of materials that absorb neutrons, such as boron or cadmium. By inserting control rods into the reactor, the number of free neutrons available for fission can be reduced, effectively controlling the rate of the fission reaction. If the rods are fully inserted, they can absorb enough neutrons to halt the fission process entirely.

The half-life of iodine-131 is 8 days. After 24 days, which is three half-lives, the remaining fraction can be calculated as follows:

After 1 half-life (8 days): 1/2 remains
After 2 half-lives (16 days): 1/4 remains
After 3 half-lives (24 days): 1/8 remains.
Thus, the fraction of iodine-131 that remains after 24 days is 1/8.