IGCSE Physics 0625 — Topic 5: Nuclear Physics

Question 1

Most of an atom is empty space. What fraction of the atom's volume is occupied by the nucleus?

AAbout one half BAbout one thousandth CAbout one ten-thousandth DAbout one thousand-billionth (10⁻¹²)

Question 2

In the Rutherford alpha-scattering experiment, a thin gold foil is bombarded with alpha particles. What observation led to the conclusion that the nucleus is positively charged?

AMost alpha particles passed straight through the foil. BSome alpha particles were deflected through small angles. CA very small number of alpha particles bounced straight back. DAlpha particles were attracted towards the foil.

Question 3

An atom of oxygen has the nuclide notation ¹⁶₈O. How many neutrons does this atom contain?

A6 B8 C16 D24

Question 4

Which row correctly shows the relative charge and relative mass of a proton?

ACharge: +1, Mass: 1 BCharge: 0, Mass: 1 CCharge: +1, Mass: 1/1836 DCharge: −1, Mass: 1

Question 5

Two atoms are isotopes of the same element. Which statement about them must be true?

AThey have the same number of neutrons but different numbers of protons. BThey have the same number of protons but different numbers of neutrons. CThey have different numbers of electrons and different numbers of protons. DThey have the same mass number but different atomic numbers.

Question 6

An atom of chlorine-37 is represented as ³⁷₁₇Cl. An atom of chlorine-35 is represented as ³⁵₁₇Cl. Which particles are present in different numbers in these two atoms?

AProtons only BElectrons only CNeutrons only DProtons and neutrons

Question 7

In nuclear fusion, two light nuclei combine to form a heavier nucleus. Where does this process occur naturally?

AIn a nuclear power station BInside the core of stars CIn rocks underground DIn the Earth’s atmosphere

Question 8

Nuclear fission involves a heavy nucleus splitting into two smaller nuclei. Which element is commonly used as fuel in a nuclear fission reactor?

AHydrogen BHelium CCarbon DUranium

Question 9

In the Rutherford alpha-scattering experiment, most alpha particles passed straight through the gold foil. What does this observation tell us about the structure of the atom?

AThe atom is mostly empty space. BThe nucleus has a positive charge. CThe nucleus contains most of the mass. DElectrons orbit in fixed energy levels.

Question 10

A neutral atom of lithium has the nuclide notation ⁷₃Li. How many electrons does this atom have?

A3 B4 C7 D10

Question 11

Which of the following is the most significant source of background radiation for most people?

ANuclear power stations BRadon gas from rocks CMobile phone signals DMedical X-rays

Question 12

A Geiger-Müller (G-M) tube is used to detect radiation. What does the G-M tube actually detect?

ATemperature changes caused by radiation BIonisation of gas inside the tube CLight produced by radioactive decay DMagnetic fields from the source

Question 13

A G-M tube records 520 counts in 10 minutes from a radioactive source. The background count rate is 20 counts per minute. What is the corrected count rate from the source?

A32 counts per minute B50 counts per minute C500 counts per minute D52 counts per minute

Question 14

Which type of radiation consists of a helium nucleus?

AAlpha (α) BBeta (β) CGamma (γ) DNeutron

Question 15

Which type of radiation has the greatest ionising power?

AAlpha BBeta CGamma DAll three have equal ionising power

Question 16

A radioactive source is placed near a G-M tube. The count rate is measured. A sheet of aluminium 5 mm thick is placed between the source and the tube. The count rate drops to background level. What type of radiation was the source emitting?

AAlpha only BBeta only CGamma only DAlpha and beta only

Question 17

Which statement about gamma radiation is correct?

AIt is deflected towards the positive plate in an electric field. BIt is an electromagnetic wave with no charge and no mass. CIt is stopped by a thin sheet of paper. DIt has a charge of +2 and a mass number of 4.

Question 18

Beta particles are deflected in a magnetic field. In which direction are they deflected compared to alpha particles in the same field?

AThe same direction, but deflected less BThe same direction, but deflected more CThe opposite direction, and deflected more DNot deflected at all

Question 19

Radioactive decay is described as random. What does this mean?

AAll nuclei in a sample decay at the same time. BIt is impossible to predict which particular nucleus will decay next. CThe decay rate increases with temperature. DThe half-life changes each time a measurement is taken.

Question 20

A nucleus of radium-226 (²²⁶₈₈Ra) decays by emitting an alpha particle. What is the nuclide notation of the daughter nucleus?

A²²²₈₆Rn B²²⁴₈₇Fr C²²²₈₈Ra D²²⁶₈₆Rn

Question 21

A nucleus of carbon-14 (¹⁴₆C) decays by emitting a beta particle. What is the daughter nucleus?

A¹⁴₇N B¹⁰₄Be C¹⁴₅B D¹³₆C

Question 22

When a nucleus emits a gamma ray, what happens to the proton number and mass number of the nucleus?

ABoth proton number and mass number decrease. BProton number increases by 1, mass number stays the same. CBoth proton number and mass number stay the same. DProton number stays the same, mass number decreases by 4.

Question 23

Radioactive decay is described as spontaneous. What does this mean?

AThe decay is caused by external conditions such as heat or pressure. BThe decay happens without any external cause and cannot be influenced. CThe decay always produces the same type of radiation. DThe decay rate can be increased by heating the source.

Question 24

A source emits radiation that is stopped by a thin sheet of paper but not by air at a range of 3 cm. Which type of radiation is the source emitting?

AAlpha only BBeta only CGamma only DBeta and gamma

Question 25

When a nucleus undergoes beta decay, which change occurs?

AA proton changes into a neutron. BA neutron changes into a proton, and an electron is emitted. CTwo protons and two neutrons are ejected as a single particle. DAn electron from the outer shell is lost.

Question 26

A graph of count rate against time for a radioactive source shows the count rate falling from 400 counts per minute to 50 counts per minute in 9 hours. What is the half-life of the source?

A1.5 hours B3 hours C4.5 hours D9 hours

Question 27

Which statement correctly defines half-life?

AThe time taken for the count rate from a source to fall to zero. BThe time taken for half the undecayed nuclei in a sample to decay. CThe time taken for the mass of a source to reduce to zero. DThe time taken for the radiation to travel half the distance to the detector.

Question 28

A radioactive sample initially contains 12 000 undecayed atoms. The half-life is 4 days. How many undecayed atoms remain after 12 days?

A6 000 B3 000 C1 500 D750

Question 29

A radioactive source has a count rate of 640 counts per minute. The background count rate is 40 counts per minute. After 3 half-lives, what will the count rate reading (including background) be?

A75 counts per minute B80 counts per minute C115 counts per minute D120 counts per minute

Question 30

A radioactive isotope used in a smoke detector needs to have a long half-life. Which is the best reason for this?

AA long half-life means the source emits more radiation per second. BA long half-life means the source does not need to be replaced frequently. CA long half-life means the radiation is more penetrating. DA long half-life means the source is safer to handle.

Question 31

The table shows the corrected count rate from a radioactive source measured over time.

Time (min)	0	6	12	18	24
Count rate (counts/min)	800	400	200	100	50

What is the half-life of the source?

A3 minutes B6 minutes C12 minutes D24 minutes

Question 32

A radioactive source has an activity of 960 Bq. After 5 hours the activity has fallen to 30 Bq. How many half-lives have passed?

A3 B4 C5 D6

Question 33

A radioactive isotope is used to monitor the thickness of paper in a factory. Which type of radiation and half-life combination is most suitable?

AAlpha source with a short half-life BBeta source with a long half-life CGamma source with a short half-life DGamma source with a long half-life

Question 34

A radioactive tracer is injected into a patient’s bloodstream to investigate blood flow. Which half-life is most appropriate for this medical use?

A30 seconds B6 hours C30 years D5 000 years

Question 35

Food can be preserved by exposing it to gamma radiation. Why is gamma radiation used rather than alpha or beta?

AGamma radiation makes the food radioactive so bacteria cannot survive. BGamma radiation can penetrate the packaging and kill bacteria inside without making the food radioactive. CGamma radiation has the greatest ionising power and so is most effective at killing bacteria. DGamma radiation has mass and charge so it stays inside the food to keep it sterile.

Question 36

Exposure to ionising radiation can damage living cells. Which of the following is a possible effect on human cells exposed to high doses of radiation?

AThe cells become stronger and more resistant to disease. BThe cells can be killed or their DNA mutated, potentially causing cancer. CThe cells become radioactive and emit radiation themselves. DThe cells grow larger but function normally.

Question 37

A worker in a laboratory handles a sealed radioactive source. Which precaution reduces the dose of radiation the worker receives?

AHolding the source as close to the body as possible BKeeping the source out of its lead-lined container for as long as possible CUsing long-handled tongs to hold the source and keeping it at arm’s length DPointing the source towards other people in the room

Question 38

There are three key safety principles when working with radioactive sources. Which row correctly lists all three?

AMaximise distance, minimise time of exposure, use appropriate shielding BMinimise distance, maximise time of exposure, use no shielding CMaximise distance, maximise time of exposure, use thick glass shielding DMinimise distance, minimise time of exposure, use lead shielding

Question 39

Which type of radiation is most dangerous if the source is swallowed or inhaled into the body?

AAlpha, because it has the highest ionising power and damages nearby cells heavily. BBeta, because it can penetrate through the body and escape. CGamma, because it has no ionising power and passes through cells undetected. DAll three types are equally dangerous inside the body.

Question 40

In a hospital, a gamma-emitting source is used to destroy a cancerous tumour. Why is the gamma beam rotated around the patient so it always passes through the tumour?

ATo ensure the gamma rays are absorbed by the tumour and do not pass through. BTo give the tumour a high total dose while spreading the dose to surrounding healthy tissue so it receives less damage. CTo make the gamma source last longer by reducing the count rate. DTo convert the gamma rays into alpha particles which are better at killing cancer cells.

Paper 2 — Multiple Choice

Section A — Atomic Structure

Section B — Radiation Detection, Types & Decay

Section C — Half-life

Section D — Safety & Applications