Radioactive Decay (Edexcel GCSE Physics)

Figure 8 shows the symbol for the nucleus of an atom of strontium‐90.

Figure 8

i) How many protons are in the nucleus of an atom of strontium‐90?

☐ A 38

☐ B 52

☐ C 90

☐ D 128

[1]

ii) How many neutrons are in the nucleus of an atom of strontium‐90?

☐ A 38

☐ B 52

☐ C 90

☐ D 128

[1]

The half‐life of strontium‐90 is 29 years.

The table in Figure 9 gives some information about how the mass of a sample of strontium‐90 changes with time.

Figure 9

Complete the table in Figure 9.

A teacher sets up an experiment to show some students how far beta particles travel in air.

Figure 10 shows some of the equipment she uses.

Figure 10

i) State the scientific name for the radioactivity detector shown in Figure 10.

The teacher also has:

• a radioactive source that emits only beta particles

• a metre rule.

[1]

ii) State two precautions the teacher must take to protect herself from the effects of radioactivity.

1 .....................................................................................................

2 .....................................................................................................

[2]

iii) Describe how the teacher could show how far beta particles travel in air.

[4]

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

Figure 4

Describe how a teacher should use a Geiger-Müller (GM) tube to compare the count-rates from two different radioactive rocks.

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.

i) Fluorine-18 is a radioactive isotope used in PET scanners for medical diagnosis.

Explain why fluorine-18 must be produced close to the hospital where it is used.

[2]

ii) Some tumours inside the body can be treated by using either alpha radiation or gamma radiation.

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

[4]

i) In a controlled chain reaction of uranium-235, which of these could cause a uranium-235 nucleus to undergo fission?

ii) The kinetic energy of one of the particles released in a fission reaction is 1.2×10^–11 J.

The mass of the particle is 1.4×10^–25 kg.

Calculate the velocity of the particle.

velocity of the particle = .................................... m/s[3]

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.

(i) Describe what happens in beta-positive decay.

[2]

(ii) Determine the missing values in the decay equation.

[2]

Define half−life.

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:

(i) State the independent variable

[1]

(ii) State the dependent variable

[1]

(iii) State the control variables for the experiment

[3]

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

The student plots the following graph of their results.

Determine the half−life of the sample.

This question is about radioactivity.

Alpha (α), beta (β) and gamma (γ) are three types of radioactive emissions.

Which statement describes all of these radioactive emissions?

Fluorine-19 is a stable isotope of the element fluorine

The element fluorine also has several radioactive isotopes.

Describe one similarity and one difference between the numbers of particles in one nucleus of fluorine-19 and one nucleus of a radioactive isotope of fluorine.

similarity ..........................................................................................................

difference ..........................................................................................................

Figure 3 shows a Geiger-Muller (G-M) tube attached to a counter.

The G-M tube is used to measure the activity of a source of beta (β) radiation.

There is an aluminium sheet between the beta source and the G-M tube.

The counter is switched on and after 1 minute shows a count of 268.

Figure 3

i) The aluminium sheet is taken away.

The counter is reset to zero and then switched on again.

A new count is taken for 1 minute.

Explain why the new count is greater than 268.

[2]

ii) The beta source is then also taken away.

The counter is reset to zero and switched on again.

A new count is taken for 1 minute.

Give a reason why there would now be a reading on the counter.

[1]

iii) State the SI unit for the activity of a radioactive source.

[1]

Radium-223 is a radioactive substance.

Radium-223 is an alpha emitter.

The half-life of radium-223 is 11 days.

A radioactive source contains 1.7 × 10²³ nuclei of radium-223.

Calculate the number of radium-223 nuclei remaining in the source after a time of 33 days.

number of radium-223 nuclei remaining = ..............................

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 represents a decay that can happen inside the nucleus of an atom.

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

Explain what can happen to the body if a person has a prolonged exposure to gamma rays.

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

i) Calculate the average count rate, in counts/s, from the graph. Show your working on the graph.

average count rate = ......................................... counts/s[2]

ii) The student says that the experiment must have been done carelessly because the data seemed quite scattered away from the best fit line. 

The teacher claims such results should be expected in radioactivity experiments.

Justify the teacher’s claim.

[2]