6.2 Radioactive Decay

Sometimes food can become contaminated with radioactive substances.

Describe the harmful effects of eating food contaminated with radioactive substances.

Gamma radiation can be used in food processing to irradiate food.

Explain why some food is irradiated with gamma radiation.

Gamma radiation is part of the electromagnetic spectrum.

When the nucleus of an atom emits a gamma ray, the number of protons in the nucleus and the number of neutrons in the nucleus do not change.

State how the nucleus does change when it emits a gamma ray.

Gamma radiation is produced by radioactive decay.

Alpha radiation and beta radiation are also produced by radioactive decay.

Compare the processes of alpha decay and beta decay.

Your answer should include what each radiation is and what effect each decay has on the original nucleus.

Which of these describes isotopes of an element?

Figure 9

Which decay is represented in Figure 9?

The half-life of cobalt-60 is 5 years.
A school cobalt source had an activity of 38.5 kBq in the year 2000.
Estimate the activity of this source in the year 2020.

activity = .............................................................. kBq

A G-M tube is connected to a counter.
A teacher places the G-M tube near to a radioactive source.
A student starts the counter and clock at the same time and writes down the readings shown on the counter every 15 s.

The student plots the readings with a line of best fit, as shown in Figure 10.

Figure 10

[2]

average count rate = .............................................................. counts/s

The teacher claims such results should be expected in radioactivity experiments.
Justify the teacher’s claim.

[2]

Figure 4 shows a Geiger-Müller (GM) tube used for measuring radioactivity.

Figure 4

A hospital uses a radioactive isotope with a half-life of 6 hours.

A technician measures a count rate of 80 counts per minute (cpm) from this isotope.

Figure 5

Complete the graph on Figure 5, as accurately as possible, to show how the count-rate from this isotope will change from the time of the first measurement.

The first point is already drawn in Figure 5.

One radioactive source used in hospitals is technetium (Tc).

Technetium is produced from the radioactive decay of molybdenum (Mo).

Complete the following nuclear equation.

Energy from the nuclei of atoms can be used in medical diagnosis and treatment.

[2]

Explain why the source of alpha radiation is usually inside the body but the source of gamma radiation can be outside the body.

[4]

Complete the table with the correct properties of alpha, beta and gamma radiation.

Plutonium−239 decays to uranium−235 through the emission of an alpha particle.

Determine the missing values in the decay equation:

Strontium−90 decays through beta−minus decay to form Yttrium−90.

Determine the missing values in the decay equation.

Fluorine−18 decays through beta−plus decay to form oxygen−18.

[2]

A student investigates the half−life of technetium with time. The box shows some of the variables in the experiment.

Using words from the box above:

The experiment uses a variety of apparatus. Draw a line to match the apparatus with its correct use.

Determine the half−life of the sample.