Radioactivity (Cambridge O Level Physics)

There are three naturally occurring isotopes of hydrogen: hydrogen-1, hydrogen-2 and hydrogen-3.

Hydrogen-1 is the simplest nuclide containing only one proton. Each isotope of hydrogen is represented by the symbol .

Write down the symbols, using nuclide notation, for:

hydrogen-1 ...................................

hydrogen-2 ...................................

hydrogen-3 ...................................

Extended

In a fusion reactor, a nucleus of hydrogen-2 and a nucleus of hydrogen-3 undergo fusion.

Fig 1.1 shows a neutron colliding with a nucleus of uranium-235, producing a number of products.

[3]

Explain how the process shown in Fig 1.1 can lead to a chain reaction.

This process releases energy.

Explain the energy transfer taking place in this reaction.

A radiation detector in a laboratory records a reading of 10 counts/min. There are no radioactive samples in the laboratory.

Fig.12.1 shows a radioactive source placed close to a radiation detector and counter. The detector can detect α, β and γ radiation.

The radioactive source emits β-particles only.

 
Describe how you could show that the source emits β-particles only.
As part of your answer, you may draw on Fig.12.1 and add any other apparatus you may need.

In the first experiment the count rate for a sample of a radioactive isotope is measured every 30 seconds for 6 minutes.

The results are shown in Table 12.1.

Estimate the half-life of the radioactive isotope. Use the information in the table.

In the second experiment the teacher repeats the procedure with another sample of the same radioactive isotope. The mass of the second sample is greater than that of the first sample.

 
Suggest a value for the count rate for this sample at the start of the experiment.

One type of particle emitted during radioactive decay is an α-particle (alpha particle).

Describe:

[1]

[1]

[1]

State the type of radioactive emission that causes

The isotope radon-220 is radioactive and it decays by α-particle emission.

An experiment takes place in a laboratory shielded from all background radiation. A sample of radioactive material is wrapped in aluminium foil of thickness 0.1 mm. A detector of ionising radiation placed 1 cm from the foil records a reading.

A piece of aluminium of thickness 5 mm is placed between the detector and the foil. The detector reading drops to zero.

 
State and explain any type of radiation passing through the aluminium foil.

Radioactive sources emit α-(alpha), β-(beta) and γ-(gamma) radiations.

State which of these types of radiation can pass through paper.

Barium-137 is a radioactive isotope. The nuclide notation for barium-137 is

Determine the number of neutrons in a nucleus of barium-137.

An isotope of barium–137 has a half-life of 3 minutes.

A radioactive source contains 36 mg of this isotope.

Calculate the mass of the isotope that remains in the source after 9 minutes.

Fig. 10.1 shows a vacuum tube with a radioactive source. The radioactive source emits α-particles, β-particles and γ -rays. There is a very strong magnetic field between the N pole and the S pole of the magnet.

The lead cylinder has a narrow central hole. State and explain the effect of the lead cylinder.

Extended

Describe the paths of the α-particles, β-particles and γ -rays as they pass through the magnetic field. Explain your answers.

Radioactive decay may include the emission of:

α-radiation

β-radiation

γ-radiation

In a factory, rollers press aluminium metal to make thin foil sheets. An automatic system for controlling the thickness of the foil uses a radioactive source. The automatic system changes the gap between the top and bottom roller. Fig. 12.1 shows the equipment.

(i)

Use your ideas about the properties of radiation to suggest and explain the type of radiation used.

 

type of radiation: ..........................................................................................

 

explanation: ..........................................................................................

[2]

 

(ii)

The aluminium foil passing the radiation detector is too thin. Describe how this fault affects the reading on the counter.

[1]

 

(iii)

Suggest how the fault in (b)(ii) is corrected. State what happens to the rollers.

[1]

 

(iv)

The source used is strontium-90. A nucleus of strontium-90 can be described as . State the number of protons in a nucleus of strontium-90.

[1]

Radon-222 is radioactive. It can be represented as .

For a neutral atom of radon-222, state

Extended

A radon-222 nucleus decays by α-particle emission to a polonium (Po) nucleus.

Complete the equation for the decay of radon-222.

Radon-222 has a half-life of 3.8 days.

At a certain time, a sample contains 6.4 × 10⁶ radon nuclei.

Calculate the number of α-particles emitted by the radon nuclei in the following 7.6 days.

number = ...........................................................

The nuclide notation describes the nucleus of one type of atom.
Draw a line from each symbol to the correct description for that symbol.

A radioactive nucleus of uranium-235 decays to a nucleus of thorium and emits an α-particle.
Complete the equation.

A nucleus of uranium-235 undergoes nuclear fission in a reactor.

The thorium produced by the decay in (a) is also radioactive and has a half-life of 26 hours.

At a certain time, a pure sample of this isotope initially contains 4.8 × 10⁹ atoms.

Calculate the number of atoms of this sample that decay in the following 52 hours.

number = ...........................................................

Table 10.1 contains details of the nature and some properties of alpha, beta and gamma emissions.

Table 10.1

Complete Table 10.1 by filling in the missing details.

Surgical instruments in sealed plastic bags are placed in thin plastic boxes. A conveyor belt takes the boxes close to a cobalt-60 source which sterilises the instruments.

This is shown in Fig. 10.1.

Fig. 10.1 (viewed from above)

The cobalt-60 source is a radioactive isotope of cobalt that emits gamma-radiation

[2]

[1]

[1]

[1]

Geiger and Marsden performed an experiment in which alpha-particles were fired at a thin film of gold.
 

(i)

Fig. 10.2 shows an alpha-particle passing close to the nucleus of a gold atom.

Fig. 10.2

Explain why the alpha-particle is deflected

. [2]

. [2]

Fig. 9.1 shows the main parts of a nuclear reactor.

Fig. 9.1

The fuel rod contains uranium-235, which can undergo nuclear fission.

Describe the process of nuclear fission that occurs in the fuel rod.

Your description should include the role of neutrons in the process.

Explain what happens as a control rod is moved out of the reactor core.

The nuclear reactor releases energy at a steady rate. 

By referring to neutrons, describe what is happening to achieve this steady rate.

Explain the purpose of the moderator in the nuclear reactor.