Chapter 1 - Radioactivity

Question 1

Name the three types of Radiation

Answer 1

Alpha
Beta
Gamma

Question 2

What was a Nucleus thought to be like before Rutherford’s model?

Answer 2

Like a currant bun - With electrons dotted in the atom like currants in a bun with the positive charge spread throughout the atom like the dough of the bun

Question 3

For Rutherford’s experiment, why did the beam of Alpha particles have to be at a constant speed?

Answer 3

To prevent the Alpha particles from colliding into each other

Question 4

For Rutherford’s experiment, why did the beam of Alpha particles have to be narrow?

Answer 4

To be more accurate when aiming for the Nucleus of an atom

Question 5

For Rutherford’s experiment, why did it have to be performed in an evacuated metal container?

Answer 5

To prevent the Alpha particles from colliding with air particles (As Alpha radiation as a small range)
(Another answer could include to prevent the Radiation from escaping)

Question 6

For Rutherford’s experiment, why did the foil have to be very thin?

Answer 6

To prevent the Alpha particles from scattering more than once

Question 7

For Rutherford’s experiment, what happened when a particle hit the fluorescent screen?

Answer 7

Light would be emitted from the spot where the particle hit

Question 8

How did Rutherford’s experiment prove that the Nucleus of an atom was relatively small compared to the atom itself?

Answer 8

Most of the particles passed straight through the atom instead of reflecting or changing direction

Question 9

How did Rutherford’s experiment prove that most of an atom’s mass was concentrated in the small region (the Nucleus) at the centre of the atom?

Answer 9

Some of the particles that were reflected collided head on and were reflected straight back (The angle of deflection was 180°). This can only happen if the mass of the Nucleus is much greater than the mass of the particle

Question 10

In Rutherford’s experiment, the electrostatic repulsion between the particle and the Nucleus increases as the separation between the two ________

Answer 10

Decreases

Question 11

During Rutherford’s experiment, why did some of the particles pass through without significantly changing direction?

Answer 11

The particles were not close enough to the Nucleus to be deflected

Question 12

Rank the three types of Radiation in order of smallest range to greatest range

Answer 12

Alpha
Beta
Gamma

Question 13

Rank the three types of Radiation in order of weakest penetration to strongest penetration

Answer 13

Alpha
Beta
Gamma

Question 14

Rank the three types of Radiation in order of weakest ionisation to strongest ionisation

Answer 14

Gamma
Beta
Alpha

Question 15

How can an ionisation chamber test the ionising effect of each type of radiation?

Answer 15

When the radiation is released inside the chamber from the source, it ionises the air particles (The chamber contains air at atmospheric pressure). Ions created are attracted to the oppositely charged electrode where they are discharged. electrons pass through the electrode into a circuit where a picoammeter is connected. The current of the circuit is proportional to the number of electrons flowing with is proportional to the number of ions per second created in the chamber due to the ionisation energy of the Radiation type.

Question 16

Define count rate

Answer 16

The number of counts recorded per second from a Radiation source

Question 17

Define corrected count rate

Answer 17

The number of counts recorded per second from a Radiation source, taking background radiation into account (And subtracting the background radiation from the recorded and calculated count rate)

Question 18

How does a Geiger tube work?

Answer 18

The geiger tube consists of a thin mica window which allows Alpha, Beta and Gamma radiation through. Gamma can also enter from the tube walls. There is a metal rod in the middle of a tube which is at a positive potential and connected to the positive terminal of a circuit. The tube wall is connected to the negative terminal and earthed. When a particle of ionising radiation enters the tube, the particle ionises the gas atoms along the track. The negative ions are attracted to the rod and the positive ions to the wall. The ions accelerate and collide with other gas atoms producing more ions, which create more ions in the same way. Many ions are created and discharged at the electrodes. A pulse of charge passes round the circuit through the resistor, causing a voltage pule across the resistor which is recorded as a single count by the pule counter.

Question 19

What is the ‘dead time’ of a Geiger tube?

Answer 19

The time taken for a Geiger tube to regain its non-conducting state after an ionising particle enters it

Question 20

If another particle enters and discharges inside a Geiger tube before the dead time has ended, what will happen?

Answer 20

The particle will not cause a voltage pulse, therefore, a count will not be recorded

Question 21

Which direction does Gamma move in?

Answer 21

It is emitted and spreads out in all directions (Like a sphere)

Question 22

What law does Gamma radiation follow?

Answer 22

The inverse square law

Question 23

Define intensity of radiation

Answer 23

The radiation energy per second passing normally through unit area

Question 24

Describe an Alpha particle

Answer 24

A helium atom (Composed of 2 protons and 2 neutrons)

Question 25

What is a Beta particle?

Answer 25

A fast moving electron

Question 26

How was a Beta particle proven to be an electron?

Answer 26

By measuring the deflection of a beam of Beta particles using electric and magnetic fields. The measurements were used to work out the specific charge of the particles. It was discovered that the specific charge of the particles were the same as electrons

Question 27

What does Gamma radiation consist of?

Answer 27

Photons

Question 28

How was it discovered that Gamma radiation consisted of Photons?

Answer 28

The discovery was made by using a crystal to diffract a beam of Gamma radiation in a similar way to the diffraction of light by a diffraction grating

Question 29

What does the inverse square law for Gamma radiation state?

Answer 29

The intensity of Gamma radiation is inversely proportional to the square of the distance

Question 30

What happens to the Atomic Number and Mass number of an atom after Alpha emission?

Answer 30

The Atomic Number decreases by 2 while the Mass Number decreases by 4

Question 31

What happens to the Proton Number and Neutron number of an atom after Alpha emission?

Answer 31

The Proton Number decreases by 2 and the Neutron Number decreases by 2

Question 32

What happens to the Atomic Number and Mass number of an atom after Beta- (Beta minus) emission?

Answer 32

The Atomic Number increases by 1 but the Mass Number doesn’t change

Question 33

What happens to the Proton Number and Neutron number of an atom after Beta- (Beta minus) emission?

Answer 33

The Proton number increases by 1 while the Neutron number decreases by 1 (A Neutron turns into a Proton)

Question 34

What happens to the Atomic Number and Mass number of an atom after Beta+ (Beta plus) emission?

Answer 34

The Atomic Number decreases by 1 but the Mass Number doesn’t change

Question 35

What happens to the Proton Number and Neutron number of an atom after Beta+ (Beta plus) emission?

Answer 35

The Proton number decreases by 1 while the Neutron number increases by 1 (A Proton turns into a Neutron)

Question 36

When does Gamma emission occur?

Answer 36

When a Nucleus has excess energy after emitting an Alpha or Beta particle

Question 37

What happens during Electron capture?

Answer 37

A Proton-rich nucleus captures and reacts with an inner-shell electron. This cause the proton in the nucleus to change into a neutron with the emission of an electron neutrino at the same time

Question 38

What else is emitted during Beta minus emission?

Answer 38

An electron anti-neutrino

Question 39

What else is emitted during Beta plus emission?

Answer 39

An electron neutrino

Question 40

How does Ionising radiation affect living cells?

Answer 40

It can destroy cell membranes which causes cells to die.
It can damage vital molecules such as DNA by creating ‘free radical’ ions which react with vital molecules. This affects cell division and nuclei become damaged. Damaged DNA may cause cells to divide and grow uncontrollably causing a tumour which could lead to cancer.

Question 41

Anyone using equipment that produces ionising radiation must wear a film badge to monitor his or her exposure to ionising radiation. How does a film badge work?

Answer 41

The badge contains a photographic film in a light-proof wrapper. Different areas of the film are covered by absorbers of different materials and thicknesses. When the film is developed the amount of exposure to each form of ionising radiation can be estimated from the blackening of the film.

Question 42

Name as many sources of background radiation as possible

Answer 42

Air (Radon Gas)
Medical Equipment
Ground and Buildings
Food and Drink
Cosmic Rays
Nuclear Weapons
Air Travel
Nuclear Power Stations
Nuclear Waste

Question 43

Why should radioactive materials be stored in lead-lined containers?

Answer 43

Radioactive sources that produce Alpha and Beta radiation also produce Gamma radiation so lead thick enough to contain the radiation is required

Question 44

What should Solid sources of radiation be transferred using?

Answer 44

Handling tools such as tongs or a glove-box using robots.

Question 45

Why should tongs with long handles be used to transfer Solid sources of radiation?

Answer 45

Long handling tools (Such as tongs) ensure that the intensity of the Gamma radiation from the source at the user is as low as possible. It also ensures that the user is beyond the range of Alpha and Beta radiation from the source.

Question 46

How should Liquid, gas and solid powder radiation sources be transferred?

Answer 46

In Sealed Containers (This is to ensure radioactive as cannot be inhaled and radioactive liquid can’t be splashed on the skin or drunk)

Question 47

Define the half-life of a Radioactive substance

Answer 47

The time taken for the mass of the isotope to decrease to half the initial mass (Or the time taken for the number of nuclei of the isotope to decrease to half the initial number)

Question 48

Why does the mass of a radioactive source decrease exponentially? (Why does a radioactive source decay at an exponential rate?)

Answer 48

Radioactive decay is a random process (For a single Nucleus) so the number of nuclei that decay in a certain tune period is in proportion to the number of nuclei remaining.

Question 49

Define the Activity of a radioactive isotope

Answer 49

The number of nuclei of the isotope that disintegrate per second (Or the rate of change of the number of nuclei of the isotope)

Question 50

What is the unit of Activity?

Answer 50

Becquerel (Bq)

1 Bq = 1 disintegration per second

Question 51

The activity of a radioactive isotope is proportional to…?

Answer 51

The Mass of the Isotope

Or the number of Nuclei remaining

Question 52

A =Activity of a Radioactive source
E = Energy of one Particle (Or Photon) emitted
The energy transfer per second from the source = ?

Answer 52

AE
A x E
Activity (of the source) x Energy (of one Particle/Photon emitted)

Question 53

Define the Decay Constant (λ) of a Radioactive isotope

Answer 53

The probability of an individual nucleus decaying per second