Nuclear

Question 1

Describe the Rutherford scattering experiment.

Answer 1

● A beam of alpha particles was directed at a thin gold foil. ● Occurs in a vacuum so that no collisions between air particles and alpha particles can occur. ● The experiment was done in order to determine the structure of an atom.

Question 2

In the Rutherford scattering experiment it was observed that most of the alpha particles passed straight through. What can we infer from that?

Answer 2

That most of the atom is made from empty space.

Question 3

What evidence was there that suggested that the nucleus had a positive charge?

Answer 3

Because the nucleus repels the alpha particles and caused them to deflect from their original path, some of them even bounced back.

Question 4

Name 3 types of radiation?

Answer 4

● Alpha ● Beta (plus and minus) ● Gamma

Question 5

Order Alpha, Gamma and Beta radiation starting with the most ionising?

Answer 5

● Alpha ● Beta ● Gamma

Question 6

Order Alpha, Gamma and Beta radiation starting with the most penetrating?

Answer 6

● Gamma ● Beta ● Alpha

Question 7

A sheet of paper can block which type of radiation?

Answer 7

Alpha radiation.

Question 8

When a nucleus decays through gamma radiation, how does the atomic number and mass number change?

Answer 8

They remain the same as the number of protons and neutrons remain the same.

Question 9

Why is ionising radiation seen as dangerous?

Answer 9

Because it can kill or mutate cells, which could lead to mutations and things such as cancer.

Question 10

Which radiation is more harmful inside a human body, alpha or gamma?

Answer 10

Alpha radiation – because it has a high ionising power so it would damage more cells. It is also very poorly penetrating, therefore it cannot leave the body, whereas gamma radiation is highly penetrating.

Question 11

Give an example of a real life use of Beta decay and explain why Beta is chosen for this.

Answer 11

Beta radiation can be used to measure the thickness of paper or aluminium foil. Alpha isn’t used as it is less penetrative and wouldn’t reach the detector on the other side. Gamma radiation is too penetrative and would pass through everything.

Question 12

Which type of radiation follows the inverse square law?

Answer 12

Gamma radiation.

Question 13

What does the inverse square law state?

Answer 13

The intensity is inversely proportional to the square of the distance from the source.

Question 14

What is intensity measured in?

Answer 14

Watts per square meter (W/m²).

Question 15

Describe an experiment which could be used to show the inverse square law and gamma rays.

Answer 15

● Measure background radiation with a Geiger-Müller tube, without the gamma source. ● Put the gamma source at a set distance (1m) and record count rate. Take averages. ● Repeat at distances increasing by 10cm. ● Subtract background radiation. ● Square each distance. ● Plot count rate against 1/d². ● A straight line through the origin confirms direct proportionality.

Question 16

What is background radiation?

Answer 16

Radiation that is constantly in the surroundings from sources such as rocks and food.

Question 17

What is the decay constant (𝜆)?

Answer 17

The probability of a nucleus decaying per second.

Question 18

What are the units for the decay constant?

Answer 18

s⁻¹

Question 19

What is half life?

Answer 19

The time it takes for half of the unstable nuclei in a substance to decay.

Question 20

What equation can you use to work out the half life of an object?

Answer 20

T½ = ln(2)/𝜆

Question 21

Complete the equation. 𝜆N = ?

Answer 21

Activity.

Question 22

What is activity measured in?

Answer 22

Bq (decays per second).

Question 23

True or false. Radioactive isotope decay exponentially.

Answer 23

True. i.e. N = N₀e⁻𝜆t

Question 24

Why is Technetium 99m useful in medicine?

Answer 24

● Because it releases gamma radiation ● It has a short half life so it doesn’t stay radioactive for long ● Half life of 6 hours: long enough to detect ● Can be made near hospitals ● Easy to detect outside the patient ● ‘Clears away’ after a few days

Question 25

Where on the curve does B⁻ decay occur and why?

Answer 25

Above the stability line, because the nuclei have too many neutrons. Beta minus decay converts a neutron into a proton, making it more stable.

Question 26

What type of decay occurs below the stability line and why?

Answer 26

Beta plus decay. Nuclei here have too many protons. Beta plus decay converts a proton into a neutron.

Question 27

How do heavier nuclei often decay?

Answer 27

Through alpha decay. Alpha decay emits a helium nucleus (2 protons and 2 neutrons), making the nucleus less heavy and more stable.

Question 28

An alpha particle is fired at a nucleus, with known kinetic energy. How can you use energy conservation to find closest approach of the particle?

Answer 28

We compare kinetic energy with electrostatic potential energy. At closest approach, Ek = Ep. Ek = ½mv², r = qQ / (4πε₀mv²).

Question 29

How is electron diffraction used to determine the diameter of a nucleus?

Answer 29

● Fire an electron beam at a thin sheet of the atom. ● A diffraction pattern appears on a screen. ● Using the angle of minima and equations, calculate the diameter.

Question 30

What is the relationship between nuclear radius (R) and nucleon number (A)?

Answer 30

R = r₀A^(1/3). Nuclear radius is proportional to the cube root of nucleon number.

Question 31

True or false. The density of a nucleus is independent of its radius.

Answer 31

True.

Question 32

What equation is used to convert mass to its energy equivalent?

Answer 32

E = mc²

Question 33

What is the mass defect?

Answer 33

The difference between the total mass of the nucleons separately compared to the actual mass of the nucleus.

Question 34

Why is there a mass defect?

Answer 34

Because energy is needed to bind the nucleus. This binding energy corresponds to a mass equivalent, so total mass decreases.

Question 35

What is binding energy?

Answer 35

The energy required to separate a nucleus into its nucleons.

Question 36

What is nuclear fission?

Answer 36

● An unstable nucleus splits into 2 smaller nuclei. ● Occurs with larger nuclei. ● Binding energy per nucleon increases, releasing energy.

Question 37

What is fusion?

Answer 37

When two small nuclei fuse to create a larger nucleus. The binding energy per nucleon increases, releasing energy.

Question 38

Why is it difficult to make fusion occur on Earth?

Answer 38

Strong repulsion between positively charged nuclei requires huge energy to overcome. It’s also hard to find materials that withstand extreme heat cost-effectively.

Question 39

How is fission used in nuclear reactors?

Answer 39

Uranium-235 absorbs neutrons, becomes unstable and splits into daughter nuclei, releasing 2–3 neutrons. These neutrons sustain the chain reaction.

Question 40

What is the purpose of a moderator?

Answer 40

To slow down neutrons so they can be absorbed by uranium, using elastic collisions.

Question 41

Why are control rods essential for a nuclear power station?

Answer 41

They prevent uncontrolled reactions by absorbing neutrons so only one neutron per fission continues the chain.

Question 42

Is Boron used as a control rod or a moderator?

Answer 42

Control rods.

Question 43

Give an example of a moderator material.

Answer 43

Water.

Question 44

What is the purpose of using water as a coolant?

Answer 44

It removes heat from the reactor to prevent overheating.

Question 45

What is the critical mass?

Answer 45

The minimum mass of fuel needed for a chain reaction to occur.

Question 46

Which waste products from a nuclear reactor cause the highest risk?

Answer 46

Spent fuel rods.

Question 47

How is high-level waste disposed of?

Answer 47

● Stored in cooling ponds ● Then sealed in steel containers and placed deep underwater

Question 48

What is low-level waste contained in?

Answer 48

Sealed in containers and buried underground until safe.