Answer

The actual initial count rate is 2000 counts/minute because background is 50 counts/minute.

The half-life is 3.0 days; therefore after 9.0 days three half-lives have elapsed.

Therefore the activity is 250 counts/minute 9.0 days later, but the background radiation count rate of 50 counts/minute is assumed constant, so the actual count rate is 300 counts/minute.

Section 7c Fission and fusion

• Radioactivity, nuclear fission and nuclear fusion are three types of nuclear reaction.They all result in a release of energy.

Fission

• Nuclear power reactors (for example, at nuclear power stations) use a nuclear reaction called nuclear fission. Fission means splitting.
• Fission occurs when an unstable large nucleus splits to form two smaller nuclei, with the release of energy.
• Two isotopes commonly used as nuclear fuels are uranium-235 and plutonium-239. Both these isotopes are large nuclei and can be split relatively easily, especially when neutrons collide with them.
• Naturally occurring uranium is mostly uranium-238, with a very small percentage of the isotope uranium-235. When a neutron strikes (collides with) a uranium-235 nucleus, the nucleus becomes unstable (uranium-236).
• The unstable uranium-236 splits into two smaller radioactive nuclei, called daughter nuclei.