Mass number, atomic number & isotopes

Figure 6 shows a diagram of a helium atom.

Complete the table for particles G and H, as shown in Figure 6.

An atom of beryllium has the symbol

Be 9 4

The beryllium atom has 4 protons.

Determine the number of neutrons in this atom.

Determine the number of electrons in this atom.

Which of these is the unit for the activity of a radioactive isotope?

The isotope nitrogen-13 (N-13) has a half-life of 10 minutes.

A sample of N-13 has an initial mass of 120 g.

Calculate the mass of N-13 that remains after 30 minutes.

mass remaining =_........

An atom has a central nucleus containing neutrons and protons.

Electrons orbit the nucleus.

Which row of the table gives the relative mass and charge of a proton?

An atom has a radius of 1.0 × 10^–10m.

A nucleus has a radius of 1.0 × 10^–15m.

Calculate the ratio of the radius of the atom to the radius of the nucleus.

Explain why an atom has no charge overall.

State the number of protons in one atom of carbon-14.

State the number of neutrons in one atom of carbon-14.

Figure 6 shows a graph for the decay of the radioactive isotope carbon-14.

Use the graph to estimate the half-life of carbon-14.

Figure 11 is the symbol for a nucleus of americium-241.

Figure 11

Americium-241 is a radioactive isotope of americium.

Americium-241 decays by emitting alpha (α) particles.

Which of these is the symbol for another radioactive isotope of americium?

Which of these is the approximate maximum distance that alpha particles can travel in air at normal atmospheric pressure?

Complete the equation in Figure 12 for americium-241 decaying into neptunium (Np).

Figure 12

The activity of a radioactive source is measured as 128 Bq.

This is shown as a point on the graph in Figure 13.

The half-life of this radioactive source is 17 s.

Use this information to plot three more points on the graph grid in Figure 13 to show how the activity of the source changes with time.

Describe what happens in the nucleus of an atom when a positron is emitted.

Figure 10 shows a safety sign on the door of a laboratory where radioactive materials are used.

State one way that radioactivity can be dangerous to humans.

State one piece of equipment that can be used to measure radioactivity.

Alpha (α) radiation and ultraviolet (UV) radiation are ionising radiations.

Give two other ionising radiations.

Sulfur‑35 is a radioactive isotope of sulfur.

Figure 11 represents a nucleus of sulfur‑35.

35 S 16

Figure 11

Draw one line from each type of particle to the number of that type of particle in a nucleus of sulfur‑35.

A sample of a radioactive isotope has a mass of 520 g.

The half‑life of the radioactive isotope is 18 days.

Calculate the mass of the original radioactive isotope remaining after 18 days.

mass after 18 days_........

Calculate the mass of the original radioactive isotope remaining after 54 days.

mass after 54 days_........

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.

Figure 14 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.

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.

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.

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

*(d) Exposing people to radioactive sources can be dangerous.

Describe the dangers of exposure to radioactive sources and what can be done to protect hospital staff when they are working with radioactive sources.

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

Sr 90 38

Figure 8

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

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

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.

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.

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.

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

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

Carbon‑13 and carbon‑14 are isotopes of carbon.

Nuclei of carbon‑13 and carbon‑14 can be represented by these symbols

13 14

Complete the table for an atom of carbon‑13 and an atom of carbon‑14.

State the name of an instrument that can be used to measure radioactivity.

State two sources of background radiation.

Carbon‑14 is radioactive and has a half‑life of 5 700 years.

The number of radioactive carbon‑14 atoms in a very old piece of wood is found to have decreased from 1 000 000 to 125 000.

Determine the age of the piece of wood.

Carbon‑14 decays into nitrogen‑14.

The symbol for nitrogen‑14 is¹⁴₇N

Explain what happens in a carbon‑14 nucleus when it decays to a nitrogen‑14 nucleus.