Nuclear Physics 1

Question 1

What did Rutherford’s scattering experiment show

Answer 1

The existence of a nucleus

Question 2

Describe the apparatus used in the Rutherford Scattering experiment

Answer 2

An alpha source and gold foil in an evacuated chamber which was covered in a fluorescent coating

A microscope that could be moved round the outside of the chamber to see where the alpha particles are hitting

Question 3

What was observed from Rutherford’s scattering experiment and what does each show

Answer 3

• Most particles passed through the foil with no deflection
  
  • Atom is mostly empty space
• A small amount of particles were deflected by a large angle
  
  • Centre of the atom is positively charged
• Very few particles were deflected by more than 90 degrees
  
  • Centre of atom is very dense

Question 4

What was the conclusion from Rutherfords scattering experiment

Answer 4

The atom has a small, dense, positively charged nucleus at its centre

Question 5

Define radiation

Answer 5

Where an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable.

Question 6

Compare the ranges in air of the 3 types of radiation

Answer 6

Alpha : lowest

Beta : middle

Gamma : Infinite

Question 7

Compare how ionising the three types of radiation are

Answer 7

Alpha : Highly

Beta : Weakly

Gamma : Very weakly

Question 8

What are the 3 types of radiation absorbed by

Answer 8

Alpha : Paper

Beta : Aluminium foil

Gamma : Metres of concrete/inches of lead

Question 9

Describe an application of the 3 types of radiation and their penetrative power

Answer 9

Monitor the thickness of certain materials while being produced

Source placed on one side of material, detector on the other side

If material gets too thick, too little radiation will pass through, so rollers will get closer together

And vice versa

Question 10

Explain 3 medical applications of gamma radiation

Answer 10

• As a detector
  
  • Injected into patients and detected for diagnosis
• Sterilise surgical equipment
• Radiation therapy
  
  • Kill cancerous cells

Question 11

State the inverse square law for gamma radiation

Answer 11

I = k / x²

I = Intensity of radiation

x = distance from source

Question 12

What is corrected count rate

How do you calculate it

Answer 12

Actual count rate caused by the source

Total count rate - background count rate

Question 13

What is the decay constant

Answer 13

Probability of a nucleus decaying per unit time

Question 14

How to calculate the decay constant

Answer 14

ΔN / ΔT = -− λN

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

Question 15

What is the exponential formula for radioactive decay

Answer 15

N = N₀e^-λt

A = A₀e^-λt

λ = Decay constant

N₀ = Initial no. of nuclei

t = time passed

N = Current no. of nuclei

A = Current Activity

A₀ = Initial activity

Question 16

Define Half life (T_1/2)

Answer 16

Time taken for the no. of nuclei to half

Question 17

Define intensity of radiation

Answer 17

Radiation energy per second passing through a unit area

Question 18

What is the equation for Intensity of radiation for Gamma source

Answer 18

Radiation energy per second / Total area

I = nhf / 4πr²

n = No. of gamma phtons emitted per second

hf = E = Energy of each gamma photon

Question 19

What is a decay curve

Answer 19

A curve showing how the mass of an isotope decreases with respect to time as it decays