11. Nuclear Radiation

Question 1

What is a mass deficit?

Answer 1

The difference in mass of nucleus and mass of its constituents.

Question 2

What is the nuclear binding energy?

Answer 2

The energy required to separate the nucleus into its constituents.

Question 3

What us one atomic unit?

Answer 3

1/12th mass of carbon-12.

Question 4

What is nuclear fission?

Answer 4

The splitting of a large nucleus into two daughter nuclei.

Question 5

Why is energy released during fission?

Answer 5

Because the smaller nuclei have a higher binding energy per nucleon

Question 6

What is nuclear fusion?

Answer 6

Where two smaller nuclei join together to form one larger nucleus.

Question 7

Why is energy released during fusion?

Answer 7

The larger nucleus has a much higher binding energy per nucleon.

Question 8

What conditions are needed for fusion?

Answer 8

High temperatures.

High density of matter (pressure)

Question 9

What is the binding energy per nucleon?

Answer 9

Energy of a nucleus divided by the number of nucleons.

Question 10

What can you deduce after plotting binding energy per nucleon by nucleon number?

Answer 10

Whether an element can undergo fission or fusion.

Question 11

Which element undergo fission and fusion?

Answer 11

• Elements smaller than iron can undergo fusion.

- Elements bigger than iron can undergo fission.

Question 12

Why are the conditions of fusion what they are?

Answer 12

High temp: as a large amount of energy is needed to overcome the electrostatic force of repulsion between nuclei.

High density of matte: so there is enough colliding protons undergoing fusion.

Question 13

What must you do before taking readings for count rate?

Answer 13

Measure the background radiation, then subtract this from your measured values.

Question 14

What are sources of background radiation?

Answer 14

• Radon gas.
• Artificial sources - caused by nuclear weapons testing and nuclear meltdowns.
• Cosmic rays.
• Rocks.

Question 15

What is radiation?

Answer 15

• Where an unstable nucleus emits energy in the form of EM waves or subatomic particles.
• This is so they become more stable

Question 16

What are the natures of the three types of radiation?

Answer 16

Alpha: an alpha particle (helium nuclei).

Beta: a fast-moving electron.

Gamma: An EM wave.

Question 17

What are the ranges of the three types of radiation in air?

Answer 17

Alpha: 2- 10 cm

Beta: about 1m

Gamma: Infinite (follows inverse square law)

Question 18

How ionising are the three types of radiation

Answer 18

Alpha: Highly

Beta: Weakly

Gamma: Very weakly

Question 19

How absorbent are the three types of radiation?

Answer 19

Alpha: absorbed by paper.

Beta: absorbed by aluminium foil.

Gamma: absorbed by several meters of concrete OR several inches of lead.

Question 20

Describe an experiment to differentiate between the different types of radiation?

Answer 20

• Using a Geiger-muller tube and counter find the background count when a radiation source is not present.
• Place the source of radiation close to the GM tube and measure the count rate.
• Place a sheet of paper between the GM tube and measure the count rate.
• If there is a considerable change then the source is emitting alpha.
• Repeat for aluminium foil and several inches of lead.

Question 21

When does alpha decay occur?

Give a general equation.

Answer 21

In large nuclei, with too many protons and neutrons.

ⁿₚX → ⁿ⁻⁴ₚ₋₂Y + ⁴₂α
(nucleon number -4
proton number -2)

Question 22

When does beta-minus decay occur?

Give a general equation.

Answer 22

In nuclei which are neutron-rich.

ⁿₚX → ⁿₚ₊₁Y + ⁰₋₁β + ᴠ̅ₑ
nucleon number +1
(ᴠ̅ₑ = electron nutrino)

Question 23

What is the decay constant?

How is it calculated?

Answer 23

The probability of a nucleus decaying per unit time.

by finding the change in the number of nuclei (ΔN) of a sample over time (Δt), over the initial number of nuclei (N).

ΔN/Δt = -λN

Question 24

What does the following formula show:

N = N₀e^(-λt)

Answer 24

The exponential decay of radioactive decay.

• N is the number of nuclei.
• N₀ is the initial number of nuclei.
• λ is the decay constant.
• t is the time passed.

Question 25

What is a half-life?

Answer 25

The time taken for the number of nuclei to halve.

Question 26

What is the activity of a radioactive sample?

Answer 26

The number of nuclei that decay per second.

Question 27

When can the decay constant not be used?

Answer 27

When there is not a large number of nuclei in a sample

as the decay constant models the number of nuclei decayed by statistical means.