Topic 7

Question 1

A freshly prepared sample contains 4.0 μg of iodine-131. After 24 days, 0.5 μg of iodine-131 remain. The best estimate of the half-life of iodine-131 is
A. 8 days.
B. 12 days.
C. 24 days.
D. 72 days.

Answer 1

A. 8 days.

Question 2

Which nucleons in a nucleus are involved in the Coulomb interaction and the strong short-range nuclear interaction?

          Coulomb interaction              Strong short-range interaction A.                 protons                                           protons, neutrons B.                 protons                                              neutrons C.                protons                                                 protons D.           protons, neutrons                                    neutrons

Answer 2

A. Coulomb interaction involves protons while strong short-range interaction involves both protons and neutrons

Question 3

Two samples of radioactive substances X and Y have the same initial activity. The half-life of X is T and the half-life of Y is 3T. After a time of 3T the ratio
activity of substance X/activity of substance Y is
A. 8.
B. 4.
C. 1/4
D. 1/8

Answer 3

C. 1/4

Question 4

The nuclear equation below is an example of the transmutation of mercury into gold.

The particle X is a
A. gamma-ray photon.
B. helium nucleus.
C. proton.
D. neutron.

Answer 4

B. helium nucleus.

Question 5

Define binding energy of a nucleus.

Answer 5

the (minimum) energy required to completely separate the
nucleons of a nucleus / the energy released when a nucleus
is assembled;

Question 6

Stable nuclei with a mass number greater than about 20, contain more neutrons than protons. By reference to the properties of the nuclear force and of the electrostatic force, suggest an explanation for this observation.

Answer 6

the electric force is repulsive/tends to split the nucleus;
the electric force acts on protons, the strong nuclear force acts on nucleons;
the nuclear force is attractive/binds the nucleons;
but the electric force is long range whereas the nuclear force is short range;
so adding more neutrons (compared to protons) contributes to
binding and does not add to tendency to split the nucleus / a
proton repels every other proton (in the nucleus) so extra neutrons
are needed for binding;

Question 7

Define the term unified atomic mass unit.

Answer 7

(1/2) the mass of an atom of carbon–12/¹²C

Question 8

State what is meant by the term isotopes.

Answer 8

(nuclei of same element with) same proton number,
different number of neutrons / OWTTE;

Question 9

Define the term radioactive half-life.

Answer 9

the time for the activity of a sample to reduce by half / time
for the number of the radioactive nuclei to halve from original value;

Question 10

State what is meant by the photoelectric effect.

Answer 10

ejection of electron from metal surface following absorption of
em radiation/photon;

Question 11

Define decay constant.

Answer 11

probability that a nucleus decays in unit time;

Question 12

Outline how the half-life of a sample of nitrogen-13 can be measured in a laboratory.

Answer 12

activity/count rate measured at regular time intervals/for at least
three half-lives;
plot graph activity/count rate versus time;
detail of determination of half-life from graph;

Question 13

Nuclei with a Z number greater than about 20 and which are stable against radioactive decay have

A. equal numbers of neutrons and protons.

B. more neutrons than protons.

C. fewer neutrons than protons.

D. no neutrons.

Answer 13

B. more neutrons than protons

Question 14

What type of single radioactive decay process does not change the value of Z, the value of N or the value of A?

A. Only beta decay

B. Only alpha decay

C. Only gamma decay

D. Both beta and gamma decay

Answer 14

C. Only gamma decay

Question 15

Two radioactive sources X and Y have the same initial activity. X has a half life of 2 hours and Y a half life of 1 hour. What is the ratio of the activities of X to Y after 4 hours?

A. 2 : 1

B. 4 : 1

C. 8 : 1

D. 16 : 1

Answer 15

B. 4 : 1

Question 16

Cathode rays consist of

A. electrons.

B. photons.

C. helium nuclei.

D. neutrons

Answer 16

A. electrons.

Question 17

Thermionic emission is

A. the emission of radiation from a hot object.

B. the emission of particles from a radioactive substance.

C. the ejection of electrons from a surface by incident radiation.

D. the emission of electrons from a hot object.

Answer 17

D. the emission of electrons from a hot object.

Question 18

Nuclide X decays with a half-life of 20 days to stable nuclide Y. At a particular time, a sample consists of nuclides X and Y in the ratio 1 : 1. How much time will elapse before the ratio becomes 1 : 3?

A. 20 days

B. 40 days

C. 60 days

D. 80 days

Answer 18

A. 20 days

Question 19

All the isotopes of an element have nuclei with the same

A. mass.

B. number of nucleons.

C. number of protons.

D. number of neutrons.

Answer 19

C. number of protons.

Question 20

A sample consists of a mixture of two radioactive nuclides X and Y, each of which decay to stable products. The half-life of X is about a day, while that of Y is about a week. If the activities due to X and Y are equal at a particular time, then a few days later the activity of the sample will be

A. due to nuclides X and Y equally.

B. entirely due to nuclide Y.

C. predominantly due to nuclide X.

D. predominantly due to nuclide Y

Answer 20

D. predominantly due to nuclide Y

Question 21

Which of the following best describes the principle of operation of a Geiger-Muller tube used to detect alpha particles?

A. The electric charge of the alpha particle is recorded as an electric pulse as it strikes the inside of the tube.

B. The alpha particle ionizes gas atoms or molecules along its path, the ions and electrons are separated and are detected as an electric pulse.

C. The alpha particle causes a flash of light in the tube, and each flash is counted electronically.

D. The alpha particle causes a nuclear reaction with a gas atom in the tube, and the reaction products produce an electric pulse.

Answer 21

B. The alpha particle ionizes gas atoms or molecules along its path, the ions and electrons are separated and are detected as an electric pulse.

Question 22

Which one of the following correctly gives the number of electrons, protons and neutrons in a neutral atom of the nuclide?

Answer 22

D. 29 electrons, 29 protons, 36 neutrons

Question 23

In the Geiger-Marsden experiment, α particles are scattered by gold nuclei. The experimental results indicate that most particles are α

A. scattered only at small angles.

B. scattered only at large angles.

C. absorbed in the target.

D. scattered back along the original direction.

Answer 23

A. scattered only at small angles.

Question 24

A sample of radioactive carbon-14 decays into a stable isotope of nitrogen. As the carbon-14 decays, the rate at which the amount of nitrogen is produced

A. decreases linearly with time.

B. increases linearly with time.

C. decreases exponentially with time.

D. increases exponentially with time.

Answer 24

C. decreases exponentially with time.

Question 25

The unified mass unit is defined as

A. the mass of one neutral atom of . ¹² ₆C

B. 1/12 of the mass of one neutral atom of ¹² ₆C

C. 1/6 of the mass of one neutral atom of . ¹² ₆C

D. the mass of the nucleus of ¹² ₆ C.

Answer 25

B. 1/12 of the mass of one neutral atom of ¹² ₆C

Question 26

Which one of the following provides direct evidence for the existence of discrete energy levels in an atom?

A. The continuous spectrum of the light emitted by a white-hot metal.

B. The line emission spectrum of a gas at low pressure.

C. The emission of gamma radiation from radioactive atoms.

D. The ionization of gas atoms when bombarded by alpha particles.

Answer 26

B. The line emission spectrum of a gas at low pressure.

Question 27

A sample of material initially contains atoms of only one radioactive isotope. Which one of the following quantities is reduced to one half of its initial value during a time equal to the half-life of the radioactive isotope?

A. Total mass of the sample

B. Total number of atoms in the sample

C. Total number of nuclei in the sample

D. Activity of the radioactive isotope in the sample

Answer 27

D. Activity of the radioactive isotope in the sample

Question 28

In a fission chain reaction,

A. energy from one fission reaction causes further fission reactions.

B. nuclei produced in one fission reaction cause further fission reactions.

C. neutrons from one fission reaction cause further fission reactions.

D. gamma radiation produced in one fission reaction causes further fission reactions.

Answer 28

C. neutrons from one fission reaction cause further fission reactions.

Question 29

Which one of the following correctly identifies the atomic (proton) number and mass (nucleon) number of a nucleus that has neutrons n and protons p?

Answer 29

B. protons represented by p, mass number represented by p+n

Question 30

In a laboratory when aluminium nuclei are bombarded with “a-particles, the following reaction may take place.

This reaction is an example of

A. nuclear fission.

B. nuclear fusion.

C. natural radioactive decay.

D. artificial transmutation.

Answer 30

D. artificial transmutation.

Question 31

Isotopes provide evidence for the existence of

A. protons.

B. electrons.

C. nuclei.

D. neutrons.

Answer 31

D. neutrons.

Question 32

An isotope of radium has a half-life of 4 days. A freshly prepared sample of this isotope contains N atoms. The time taken for 7N/8 of the atoms of this isotope to decay is

A. 32 days.

B. 16 days.

C. 12 days.

D. 8 days.

Answer 32

C. 12 days.

Question 33

The presence of neutrons inside the nucleus is supported by the existence of

A. isotopes.

B. orbiting electrons.

C. gamma radiation.

D. neutral atoms.

Answer 33

A. isotopes.

Question 34

The source of the Sun’s energy is

A. fission.

B. radioactivity.

C. fusion.

D. ionization.

Answer 34

C. fusion.

Question 35

In an α-particle scattering experiment (Geiger-Marsden experiment), the number n of particles incident per unit time on a detector was determined for different angles of deflection θ.

Answer 35

C

Question 36

The existence of isotopes provides evidence for the presence of

A. electrons in atomic energy levels.

B. electrons in the nuclei of atoms.

C. neutrons in the nuclei of atoms.

D. protons in the nuclei of atoms.

Answer 36

C. neutrons in the nuclei of atoms.

Question 37

Ag-102, Ag-103 and Ag-104 are three isotopes of the element silver. Which one of the following is a true statement about the nuclei of these isotopes?

A. All have the same mass.

B. All have the same number of nucleons.

C. All have the same number of neutrons.

D. All have the same number of protons.

Answer 37

D. All have the same number of protons.

Question 38

Radioactive decay is a random process. This means that

A. a radioactive sample will decay continuously.

B. some nuclei will decay faster than others.

C. it cannot be predicted how much energy will be released.

D. it cannot be predicted when a particular nucleus will decay

Answer 38

D. it cannot be predicted when a particular nucleus will decay

Question 39

The emission and absorption spectra of different elements provides evidence for the existence of

A. isotopes.

B. neutrons.

C. protons.

D. atomic energy levels.

Answer 39

D. atomic energy levels.

Question 40

The nucleus of an atom contains protons. The protons are prevented from flying apart by

A. the presence of orbiting electrons.

B. the presence of gravitational forces.

C. the presence of strong attractive nuclear forces.

D. the absence of Coulomb repulsive forces at nuclear distances.

Answer 40

C. the presence of strong attractive nuclear forces.

Question 41

Which of the following gives the correct number of protons and number of neutrons in the nucleus of ?

Answer 41

A. 5 protons, 6 neutrons

Question 42

The unified mass unit is defined as the rest mass of

A. a proton.

B. an atom of carbon-12 divided by 12.

C. an atom of carbon-12.

D. an atom of hydrogen-1.

Answer 42

B. an atom of carbon-12 divided by 12.

Question 43

Which one of the following provides evidence for a nuclear model of the atom?

A. Natural radioactive decay

B. The ionizing properties of radiation

C. The stability of certain elements

D. The scattering of alpha particles by gold foil

Answer 43

D. The scattering of alpha particles by gold foil

Question 44

When the isotope aluminium-27 is bombarded with alpha particles, the following nuclear reaction can take place.

Which one of the following correctly gives the atomic (proton) number and mass (nucleon) number of the nucleus X?

Answer 44

A. 15 protons, 30 nucleons

Question 45

The main source of the Sun’s energy is

A. chemical reaction.

B. natural radioactivity.

C. nuclear fusion.

D. nuclear fission.

Answer 45

C. nuclear fusion.

Question 46

Which of the following identifies the significant interaction(s) between nucleons inside the nucleus?

A. Nuclear only

B. Coulomb only

C. Nuclear and Coulomb

D. Gravitational, nuclear and Coulomb

Answer 46

C. Nuclear and Coulomb

Question 47

The initial activity of a sample of a radioactive isotope of half-life 10 hours is A. What is the age of the sample when its activity is A/32 ?

A. 30 hours

B. 40 hours

C. 50 hours

D. 320 hours

Answer 47

C. 50 hours

Question 48

Two light nuclei of masses m1 and m2 fuse in a nuclear reaction to form a nucleus of mass M. Which of the following expressions correctly relates the masses of the nuclei?

A. M > m1 + m2

B. M < m1 + m2

C. M=m1 + m2

D. M=m1 − m2

Answer 48

B. M < m1 + m2